Merge tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs

Pull notification queue from David Howells:
"This adds a general notification queue concept and adds an event
source for keys/keyrings, such as linking and unlinking keys and
changing their attributes.

Thanks to Debarshi Ray, we do have a pull request to use this to fix a
problem with gnome-online-accounts - as mentioned last time:

https://gitlab.gnome.org/GNOME/gnome-online-accounts/merge_requests/47

Without this, g-o-a has to constantly poll a keyring-based kerberos
cache to find out if kinit has changed anything.

[ There are other notification pending: mount/sb fsinfo notifications
for libmount that Karel Zak and Ian Kent have been working on, and
Christian Brauner would like to use them in lxc, but let's see how
this one works first ]

LSM hooks are included:

- A set of hooks are provided that allow an LSM to rule on whether or
not a watch may be set. Each of these hooks takes a different
"watched object" parameter, so they're not really shareable. The
LSM should use current's credentials. [Wanted by SELinux & Smack]

- A hook is provided to allow an LSM to rule on whether or not a
particular message may be posted to a particular queue. This is
given the credentials from the event generator (which may be the
system) and the watch setter. [Wanted by Smack]

I've provided SELinux and Smack with implementations of some of these
hooks.

WHY
===

Key/keyring notifications are desirable because if you have your
kerberos tickets in a file/directory, your Gnome desktop will monitor
that using something like fanotify and tell you if your credentials
cache changes.

However, we also have the ability to cache your kerberos tickets in
the session, user or persistent keyring so that it isn't left around
on disk across a reboot or logout. Keyrings, however, cannot currently
be monitored asynchronously, so the desktop has to poll for it - not
so good on a laptop. This facility will allow the desktop to avoid the
need to poll.

DESIGN DECISIONS
================

- The notification queue is built on top of a standard pipe. Messages
are effectively spliced in. The pipe is opened with a special flag:

pipe2(fds, O_NOTIFICATION_PIPE);

The special flag has the same value as O_EXCL (which doesn't seem
like it will ever be applicable in this context)[?]. It is given up
front to make it a lot easier to prohibit splice&co from accessing
the pipe.

[?] Should this be done some other way? I'd rather not use up a new
O_* flag if I can avoid it - should I add a pipe3() system call
instead?

The pipe is then configured::

ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, queue_depth);
ioctl(fds[1], IOC_WATCH_QUEUE_SET_FILTER, &filter);

Messages are then read out of the pipe using read().

- It should be possible to allow write() to insert data into the
notification pipes too, but this is currently disabled as the
kernel has to be able to insert messages into the pipe *without*
holding pipe->mutex and the code to make this work needs careful
auditing.

- sendfile(), splice() and vmsplice() are disabled on notification
pipes because of the pipe->mutex issue and also because they
sometimes want to revert what they just did - but one or more
notification messages might've been interleaved in the ring.

- The kernel inserts messages with the wait queue spinlock held. This
means that pipe_read() and pipe_write() have to take the spinlock
to update the queue pointers.

- Records in the buffer are binary, typed and have a length so that
they can be of varying size.

This allows multiple heterogeneous sources to share a common
buffer; there are 16 million types available, of which I've used
just a few, so there is scope for others to be used. Tags may be
specified when a watchpoint is created to help distinguish the
sources.

- Records are filterable as types have up to 256 subtypes that can be
individually filtered. Other filtration is also available.

- Notification pipes don't interfere with each other; each may be
bound to a different set of watches. Any particular notification
will be copied to all the queues that are currently watching for it
- and only those that are watching for it.

- When recording a notification, the kernel will not sleep, but will
rather mark a queue as having lost a message if there's
insufficient space. read() will fabricate a loss notification
message at an appropriate point later.

- The notification pipe is created and then watchpoints are attached
to it, using one of:

keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
watch_mount(AT_FDCWD, "/", 0, fd, 0x02);
watch_sb(AT_FDCWD, "/mnt", 0, fd, 0x03);

where in both cases, fd indicates the queue and the number after is
a tag between 0 and 255.

- Watches are removed if either the notification pipe is destroyed or
the watched object is destroyed. In the latter case, a message will
be generated indicating the enforced watch removal.

Things I want to avoid:

- Introducing features that make the core VFS dependent on the
network stack or networking namespaces (ie. usage of netlink).

- Dumping all this stuff into dmesg and having a daemon that sits
there parsing the output and distributing it as this then puts the
responsibility for security into userspace and makes handling
namespaces tricky. Further, dmesg might not exist or might be
inaccessible inside a container.

- Letting users see events they shouldn't be able to see.

TESTING AND MANPAGES
====================

- The keyutils tree has a pipe-watch branch that has keyctl commands
for making use of notifications. Proposed manual pages can also be
found on this branch, though a couple of them really need to go to
the main manpages repository instead.

If the kernel supports the watching of keys, then running "make
test" on that branch will cause the testing infrastructure to spawn
a monitoring process on the side that monitors a notifications pipe
for all the key/keyring changes induced by the tests and they'll
all be checked off to make sure they happened.

https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/keyutils.git/log/?h=pipe-watch

- A test program is provided (samples/watch_queue/watch_test) that
can be used to monitor for keyrings, mount and superblock events.
Information on the notifications is simply logged to stdout"

* tag 'notifications-20200601' of git://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs:
smack: Implement the watch_key and post_notification hooks
selinux: Implement the watch_key security hook
keys: Make the KEY_NEED_* perms an enum rather than a mask
pipe: Add notification lossage handling
pipe: Allow buffers to be marked read-whole-or-error for notifications
Add sample notification program
watch_queue: Add a key/keyring notification facility
security: Add hooks to rule on setting a watch
pipe: Add general notification queue support
pipe: Add O_NOTIFICATION_PIPE
security: Add a hook for the point of notification insertion
uapi: General notification queue definitions

Documentation/security/keys/core.rst

···
      written into the output buffer.  Verification returns 0 on success.
 
 
+  *  Watch a key or keyring for changes::
+
+	long keyctl(KEYCTL_WATCH_KEY, key_serial_t key, int queue_fd,
+		    const struct watch_notification_filter *filter);
+
+     This will set or remove a watch for changes on the specified key or
+     keyring.
+
+     "key" is the ID of the key to be watched.
+
+     "queue_fd" is a file descriptor referring to an open "/dev/watch_queue"
+     which manages the buffer into which notifications will be delivered.
+
+     "filter" is either NULL to remove a watch or a filter specification to
+     indicate what events are required from the key.
+
+     See Documentation/watch_queue.rst for more information.
+
+     Note that only one watch may be emplaced for any particular { key,
+     queue_fd } combination.
+
+     Notification records look like::
+
+	struct key_notification {
+		struct watch_notification watch;
+		__u32	key_id;
+		__u32	aux;
+	};
+
+     In this, watch::type will be "WATCH_TYPE_KEY_NOTIFY" and subtype will be
+     one of::
+
+	NOTIFY_KEY_INSTANTIATED
+	NOTIFY_KEY_UPDATED
+	NOTIFY_KEY_LINKED
+	NOTIFY_KEY_UNLINKED
+	NOTIFY_KEY_CLEARED
+	NOTIFY_KEY_REVOKED
+	NOTIFY_KEY_INVALIDATED
+	NOTIFY_KEY_SETATTR
+
+     Where these indicate a key being instantiated/rejected, updated, a link
+     being made in a keyring, a link being removed from a keyring, a keyring
+     being cleared, a key being revoked, a key being invalidated or a key
+     having one of its attributes changed (user, group, perm, timeout,
+     restriction).
+
+     If a watched key is deleted, a basic watch_notification will be issued
+     with "type" set to WATCH_TYPE_META and "subtype" set to
+     watch_meta_removal_notification.  The watchpoint ID will be set in the
+     "info" field.
+
+     This needs to be configured by enabling:
+
+	"Provide key/keyring change notifications" (KEY_NOTIFICATIONS)
+
+
 Kernel Services
 ===============
 

Documentation/userspace-api/ioctl/ioctl-number.rst

···
 'W'   00-1F  linux/wanrouter.h                                       conflict! (pre 3.9)
 'W'   00-3F  sound/asound.h                                          conflict!
 'W'   40-5F  drivers/pci/switch/switchtec.c
+'W'   60-61  linux/watch_queue.h
 'X'   all    fs/xfs/xfs_fs.h,                                        conflict!
              fs/xfs/linux-2.6/xfs_ioctl32.h,
              include/linux/falloc.h,

Documentation/watch_queue.rst

···
+==============================
+General notification mechanism
+==============================
+
+The general notification mechanism is built on top of the standard pipe driver
+whereby it effectively splices notification messages from the kernel into pipes
+opened by userspace.  This can be used in conjunction with::
+
+  * Key/keyring notifications
+
+
+The notifications buffers can be enabled by:
+
+	"General setup"/"General notification queue"
+	(CONFIG_WATCH_QUEUE)
+
+This document has the following sections:
+
+.. contents:: :local:
+
+
+Overview
+========
+
+This facility appears as a pipe that is opened in a special mode.  The pipe's
+internal ring buffer is used to hold messages that are generated by the kernel.
+These messages are then read out by read().  Splice and similar are disabled on
+such pipes due to them wanting to, under some circumstances, revert their
+additions to the ring - which might end up interleaved with notification
+messages.
+
+The owner of the pipe has to tell the kernel which sources it would like to
+watch through that pipe.  Only sources that have been connected to a pipe will
+insert messages into it.  Note that a source may be bound to multiple pipes and
+insert messages into all of them simultaneously.
+
+Filters may also be emplaced on a pipe so that certain source types and
+subevents can be ignored if they're not of interest.
+
+A message will be discarded if there isn't a slot available in the ring or if
+no preallocated message buffer is available.  In both of these cases, read()
+will insert a WATCH_META_LOSS_NOTIFICATION message into the output buffer after
+the last message currently in the buffer has been read.
+
+Note that when producing a notification, the kernel does not wait for the
+consumers to collect it, but rather just continues on.  This means that
+notifications can be generated whilst spinlocks are held and also protects the
+kernel from being held up indefinitely by a userspace malfunction.
+
+
+Message Structure
+=================
+
+Notification messages begin with a short header::
+
+	struct watch_notification {
+		__u32	type:24;
+		__u32	subtype:8;
+		__u32	info;
+	};
+
+"type" indicates the source of the notification record and "subtype" indicates
+the type of record from that source (see the Watch Sources section below).  The
+type may also be "WATCH_TYPE_META".  This is a special record type generated
+internally by the watch queue itself.  There are two subtypes:
+
+  * WATCH_META_REMOVAL_NOTIFICATION
+  * WATCH_META_LOSS_NOTIFICATION
+
+The first indicates that an object on which a watch was installed was removed
+or destroyed and the second indicates that some messages have been lost.
+
+"info" indicates a bunch of things, including:
+
+  * The length of the message in bytes, including the header (mask with
+    WATCH_INFO_LENGTH and shift by WATCH_INFO_LENGTH__SHIFT).  This indicates
+    the size of the record, which may be between 8 and 127 bytes.
+
+  * The watch ID (mask with WATCH_INFO_ID and shift by WATCH_INFO_ID__SHIFT).
+    This indicates that caller's ID of the watch, which may be between 0
+    and 255.  Multiple watches may share a queue, and this provides a means to
+    distinguish them.
+
+  * A type-specific field (WATCH_INFO_TYPE_INFO).  This is set by the
+    notification producer to indicate some meaning specific to the type and
+    subtype.
+
+Everything in info apart from the length can be used for filtering.
+
+The header can be followed by supplementary information.  The format of this is
+at the discretion is defined by the type and subtype.
+
+
+Watch List (Notification Source) API
+====================================
+
+A "watch list" is a list of watchers that are subscribed to a source of
+notifications.  A list may be attached to an object (say a key or a superblock)
+or may be global (say for device events).  From a userspace perspective, a
+non-global watch list is typically referred to by reference to the object it
+belongs to (such as using KEYCTL_NOTIFY and giving it a key serial number to
+watch that specific key).
+
+To manage a watch list, the following functions are provided:
+
+  * ``void init_watch_list(struct watch_list *wlist,
+			   void (*release_watch)(struct watch *wlist));``
+
+    Initialise a watch list.  If ``release_watch`` is not NULL, then this
+    indicates a function that should be called when the watch_list object is
+    destroyed to discard any references the watch list holds on the watched
+    object.
+
+  * ``void remove_watch_list(struct watch_list *wlist);``
+
+    This removes all of the watches subscribed to a watch_list and frees them
+    and then destroys the watch_list object itself.
+
+
+Watch Queue (Notification Output) API
+=====================================
+
+A "watch queue" is the buffer allocated by an application that notification
+records will be written into.  The workings of this are hidden entirely inside
+of the pipe device driver, but it is necessary to gain a reference to it to set
+a watch.  These can be managed with:
+
+  * ``struct watch_queue *get_watch_queue(int fd);``
+
+    Since watch queues are indicated to the kernel by the fd of the pipe that
+    implements the buffer, userspace must hand that fd through a system call.
+    This can be used to look up an opaque pointer to the watch queue from the
+    system call.
+
+  * ``void put_watch_queue(struct watch_queue *wqueue);``
+
+    This discards the reference obtained from ``get_watch_queue()``.
+
+
+Watch Subscription API
+======================
+
+A "watch" is a subscription on a watch list, indicating the watch queue, and
+thus the buffer, into which notification records should be written.  The watch
+queue object may also carry filtering rules for that object, as set by
+userspace.  Some parts of the watch struct can be set by the driver::
+
+	struct watch {
+		union {
+			u32		info_id;	/* ID to be OR'd in to info field */
+			...
+		};
+		void			*private;	/* Private data for the watched object */
+		u64			id;		/* Internal identifier */
+		...
+	};
+
+The ``info_id`` value should be an 8-bit number obtained from userspace and
+shifted by WATCH_INFO_ID__SHIFT.  This is OR'd into the WATCH_INFO_ID field of
+struct watch_notification::info when and if the notification is written into
+the associated watch queue buffer.
+
+The ``private`` field is the driver's data associated with the watch_list and
+is cleaned up by the ``watch_list::release_watch()`` method.
+
+The ``id`` field is the source's ID.  Notifications that are posted with a
+different ID are ignored.
+
+The following functions are provided to manage watches:
+
+  * ``void init_watch(struct watch *watch, struct watch_queue *wqueue);``
+
+    Initialise a watch object, setting its pointer to the watch queue, using
+    appropriate barriering to avoid lockdep complaints.
+
+  * ``int add_watch_to_object(struct watch *watch, struct watch_list *wlist);``
+
+    Subscribe a watch to a watch list (notification source).  The
+    driver-settable fields in the watch struct must have been set before this
+    is called.
+
+  * ``int remove_watch_from_object(struct watch_list *wlist,
+				   struct watch_queue *wqueue,
+				   u64 id, false);``
+
+    Remove a watch from a watch list, where the watch must match the specified
+    watch queue (``wqueue``) and object identifier (``id``).  A notification
+    (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue to
+    indicate that the watch got removed.
+
+  * ``int remove_watch_from_object(struct watch_list *wlist, NULL, 0, true);``
+
+    Remove all the watches from a watch list.  It is expected that this will be
+    called preparatory to destruction and that the watch list will be
+    inaccessible to new watches by this point.  A notification
+    (``WATCH_META_REMOVAL_NOTIFICATION``) is sent to the watch queue of each
+    subscribed watch to indicate that the watch got removed.
+
+
+Notification Posting API
+========================
+
+To post a notification to watch list so that the subscribed watches can see it,
+the following function should be used::
+
+	void post_watch_notification(struct watch_list *wlist,
+				     struct watch_notification *n,
+				     const struct cred *cred,
+				     u64 id);
+
+The notification should be preformatted and a pointer to the header (``n``)
+should be passed in.  The notification may be larger than this and the size in
+units of buffer slots is noted in ``n->info & WATCH_INFO_LENGTH``.
+
+The ``cred`` struct indicates the credentials of the source (subject) and is
+passed to the LSMs, such as SELinux, to allow or suppress the recording of the
+note in each individual queue according to the credentials of that queue
+(object).
+
+The ``id`` is the ID of the source object (such as the serial number on a key).
+Only watches that have the same ID set in them will see this notification.
+
+
+Watch Sources
+=============
+
+Any particular buffer can be fed from multiple sources.  Sources include:
+
+  * WATCH_TYPE_KEY_NOTIFY
+
+    Notifications of this type indicate changes to keys and keyrings, including
+    the changes of keyring contents or the attributes of keys.
+
+    See Documentation/security/keys/core.rst for more information.
+
+
+Event Filtering
+===============
+
+Once a watch queue has been created, a set of filters can be applied to limit
+the events that are received using::
+
+	struct watch_notification_filter filter = {
+		...
+	};
+	ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter)
+
+The filter description is a variable of type::
+
+	struct watch_notification_filter {
+		__u32	nr_filters;
+		__u32	__reserved;
+		struct watch_notification_type_filter filters[];
+	};
+
+Where "nr_filters" is the number of filters in filters[] and "__reserved"
+should be 0.  The "filters" array has elements of the following type::
+
+	struct watch_notification_type_filter {
+		__u32	type;
+		__u32	info_filter;
+		__u32	info_mask;
+		__u32	subtype_filter[8];
+	};
+
+Where:
+
+  * ``type`` is the event type to filter for and should be something like
+    "WATCH_TYPE_KEY_NOTIFY"
+
+  * ``info_filter`` and ``info_mask`` act as a filter on the info field of the
+    notification record.  The notification is only written into the buffer if::
+
+	(watch.info & info_mask) == info_filter
+
+    This could be used, for example, to ignore events that are not exactly on
+    the watched point in a mount tree.
+
+  * ``subtype_filter`` is a bitmask indicating the subtypes that are of
+    interest.  Bit 0 of subtype_filter[0] corresponds to subtype 0, bit 1 to
+    subtype 1, and so on.
+
+If the argument to the ioctl() is NULL, then the filters will be removed and
+all events from the watched sources will come through.
+
+
+Userspace Code Example
+======================
+
+A buffer is created with something like the following::
+
+	pipe2(fds, O_TMPFILE);
+	ioctl(fds[1], IOC_WATCH_QUEUE_SET_SIZE, 256);
+
+It can then be set to receive keyring change notifications::
+
+	keyctl(KEYCTL_WATCH_KEY, KEY_SPEC_SESSION_KEYRING, fds[1], 0x01);
+
+The notifications can then be consumed by something like the following::
+
+	static void consumer(int rfd, struct watch_queue_buffer *buf)
+	{
+		unsigned char buffer[128];
+		ssize_t buf_len;
+
+		while (buf_len = read(rfd, buffer, sizeof(buffer)),
+		       buf_len > 0
+		       ) {
+			void *p = buffer;
+			void *end = buffer + buf_len;
+			while (p < end) {
+				union {
+					struct watch_notification n;
+					unsigned char buf1[128];
+				} n;
+				size_t largest, len;
+
+				largest = end - p;
+				if (largest > 128)
+					largest = 128;
+				memcpy(&n, p, largest);
+
+				len = (n->info & WATCH_INFO_LENGTH) >>
+					WATCH_INFO_LENGTH__SHIFT;
+				if (len == 0 || len > largest)
+					return;
+
+				switch (n.n.type) {
+				case WATCH_TYPE_META:
+					got_meta(&n.n);
+				case WATCH_TYPE_KEY_NOTIFY:
+					saw_key_change(&n.n);
+					break;
+				}
+
+				p += len;
+			}
+		}
+	}

fs/pipe.c

···
 #include <linux/syscalls.h>
 #include <linux/fcntl.h>
 #include <linux/memcontrol.h>
+#include <linux/watch_queue.h>
 
 #include <linux/uaccess.h>
 #include <asm/ioctls.h>
···
 		unsigned int tail = pipe->tail;
 		unsigned int mask = pipe->ring_size - 1;
 
+#ifdef CONFIG_WATCH_QUEUE
+		if (pipe->note_loss) {
+			struct watch_notification n;
+
+			if (total_len < 8) {
+				if (ret == 0)
+					ret = -ENOBUFS;
+				break;
+			}
+
+			n.type = WATCH_TYPE_META;
+			n.subtype = WATCH_META_LOSS_NOTIFICATION;
+			n.info = watch_sizeof(n);
+			if (copy_to_iter(&n, sizeof(n), to) != sizeof(n)) {
+				if (ret == 0)
+					ret = -EFAULT;
+				break;
+			}
+			ret += sizeof(n);
+			total_len -= sizeof(n);
+			pipe->note_loss = false;
+		}
+#endif
+
 		if (!pipe_empty(head, tail)) {
 			struct pipe_buffer *buf = &pipe->bufs[tail & mask];
 			size_t chars = buf->len;
 			size_t written;
 			int error;
 
-			if (chars > total_len)
+			if (chars > total_len) {
+				if (buf->flags & PIPE_BUF_FLAG_WHOLE) {
+					if (ret == 0)
+						ret = -ENOBUFS;
+					break;
+				}
 				chars = total_len;
+			}
 
 			error = pipe_buf_confirm(pipe, buf);
 			if (error) {
···
 			if (!buf->len) {
 				pipe_buf_release(pipe, buf);
 				spin_lock_irq(&pipe->rd_wait.lock);
+#ifdef CONFIG_WATCH_QUEUE
+				if (buf->flags & PIPE_BUF_FLAG_LOSS)
+					pipe->note_loss = true;
+#endif
 				tail++;
 				pipe->tail = tail;
 				spin_unlock_irq(&pipe->rd_wait.lock);
···
 		ret = -EPIPE;
 		goto out;
 	}
+
+#ifdef CONFIG_WATCH_QUEUE
+	if (pipe->watch_queue) {
+		ret = -EXDEV;
+		goto out;
+	}
+#endif
 
 	/*
 	 * Only wake up if the pipe started out empty, since
···
 	int count, head, tail, mask;
 
 	switch (cmd) {
-		case FIONREAD:
-			__pipe_lock(pipe);
-			count = 0;
-			head = pipe->head;
-			tail = pipe->tail;
-			mask = pipe->ring_size - 1;
+	case FIONREAD:
+		__pipe_lock(pipe);
+		count = 0;
+		head = pipe->head;
+		tail = pipe->tail;
+		mask = pipe->ring_size - 1;
 
-			while (tail != head) {
-				count += pipe->bufs[tail & mask].len;
-				tail++;
-			}
-			__pipe_unlock(pipe);
+		while (tail != head) {
+			count += pipe->bufs[tail & mask].len;
+			tail++;
+		}
+		__pipe_unlock(pipe);
 
-			return put_user(count, (int __user *)arg);
-		default:
-			return -ENOIOCTLCMD;
+		return put_user(count, (int __user *)arg);
+
+#ifdef CONFIG_WATCH_QUEUE
+	case IOC_WATCH_QUEUE_SET_SIZE: {
+		int ret;
+		__pipe_lock(pipe);
+		ret = watch_queue_set_size(pipe, arg);
+		__pipe_unlock(pipe);
+		return ret;
+	}
+
+	case IOC_WATCH_QUEUE_SET_FILTER:
+		return watch_queue_set_filter(
+			pipe, (struct watch_notification_filter __user *)arg);
+#endif
+
+	default:
+		return -ENOIOCTLCMD;
 	}
 }
 
···
 	return retval;
 }
 
-static unsigned long account_pipe_buffers(struct user_struct *user,
-                                 unsigned long old, unsigned long new)
+unsigned long account_pipe_buffers(struct user_struct *user,
+				   unsigned long old, unsigned long new)
 {
 	return atomic_long_add_return(new - old, &user->pipe_bufs);
 }
 
-static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
+bool too_many_pipe_buffers_soft(unsigned long user_bufs)
 {
 	unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
 
 	return soft_limit && user_bufs > soft_limit;
 }
 
-static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
+bool too_many_pipe_buffers_hard(unsigned long user_bufs)
 {
 	unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
 
 	return hard_limit && user_bufs > hard_limit;
 }
 
-static bool is_unprivileged_user(void)
+bool pipe_is_unprivileged_user(void)
 {
 	return !capable(CAP_SYS_RESOURCE) && !capable(CAP_SYS_ADMIN);
 }
···
 
 	user_bufs = account_pipe_buffers(user, 0, pipe_bufs);
 
-	if (too_many_pipe_buffers_soft(user_bufs) && is_unprivileged_user()) {
+	if (too_many_pipe_buffers_soft(user_bufs) && pipe_is_unprivileged_user()) {
 		user_bufs = account_pipe_buffers(user, pipe_bufs, 1);
 		pipe_bufs = 1;
 	}
 
-	if (too_many_pipe_buffers_hard(user_bufs) && is_unprivileged_user())
+	if (too_many_pipe_buffers_hard(user_bufs) && pipe_is_unprivileged_user())
 		goto out_revert_acct;
 
 	pipe->bufs = kcalloc(pipe_bufs, sizeof(struct pipe_buffer),
···
 		pipe->r_counter = pipe->w_counter = 1;
 		pipe->max_usage = pipe_bufs;
 		pipe->ring_size = pipe_bufs;
+		pipe->nr_accounted = pipe_bufs;
 		pipe->user = user;
 		mutex_init(&pipe->mutex);
 		return pipe;
···
 {
 	int i;
 
-	(void) account_pipe_buffers(pipe->user, pipe->ring_size, 0);
+#ifdef CONFIG_WATCH_QUEUE
+	if (pipe->watch_queue) {
+		watch_queue_clear(pipe->watch_queue);
+		put_watch_queue(pipe->watch_queue);
+	}
+#endif
+
+	(void) account_pipe_buffers(pipe->user, pipe->nr_accounted, 0);
 	free_uid(pipe->user);
 	for (i = 0; i < pipe->ring_size; i++) {
 		struct pipe_buffer *buf = pipe->bufs + i;
···
 	if (!inode)
 		return -ENFILE;
 
+	if (flags & O_NOTIFICATION_PIPE) {
+#ifdef CONFIG_WATCH_QUEUE
+		if (watch_queue_init(inode->i_pipe) < 0) {
+			iput(inode);
+			return -ENOMEM;
+		}
+#else
+		return -ENOPKG;
+#endif
+	}
+
 	f = alloc_file_pseudo(inode, pipe_mnt, "",
 				O_WRONLY | (flags & (O_NONBLOCK | O_DIRECT)),
 				&pipefifo_fops);
···
 	int error;
 	int fdw, fdr;
 
-	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
+	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_NOTIFICATION_PIPE))
 		return -EINVAL;
 
 	error = create_pipe_files(files, flags);
···
 }
 
 /*
- * Allocate a new array of pipe buffers and copy the info over. Returns the
- * pipe size if successful, or return -ERROR on error.
+ * Resize the pipe ring to a number of slots.
  */
-static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots)
 {
 	struct pipe_buffer *bufs;
-	unsigned int size, nr_slots, head, tail, mask, n;
-	unsigned long user_bufs;
-	long ret = 0;
-
-	size = round_pipe_size(arg);
-	nr_slots = size >> PAGE_SHIFT;
-
-	if (!nr_slots)
-		return -EINVAL;
-
-	/*
-	 * If trying to increase the pipe capacity, check that an
-	 * unprivileged user is not trying to exceed various limits
-	 * (soft limit check here, hard limit check just below).
-	 * Decreasing the pipe capacity is always permitted, even
-	 * if the user is currently over a limit.
-	 */
-	if (nr_slots > pipe->ring_size &&
-			size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
-		return -EPERM;
-
-	user_bufs = account_pipe_buffers(pipe->user, pipe->ring_size, nr_slots);
-
-	if (nr_slots > pipe->ring_size &&
-			(too_many_pipe_buffers_hard(user_bufs) ||
-			 too_many_pipe_buffers_soft(user_bufs)) &&
-			is_unprivileged_user()) {
-		ret = -EPERM;
-		goto out_revert_acct;
-	}
+	unsigned int head, tail, mask, n;
 
 	/*
 	 * We can shrink the pipe, if arg is greater than the ring occupancy.
···
 	head = pipe->head;
 	tail = pipe->tail;
 	n = pipe_occupancy(pipe->head, pipe->tail);
-	if (nr_slots < n) {
-		ret = -EBUSY;
-		goto out_revert_acct;
-	}
+	if (nr_slots < n)
+		return -EBUSY;
 
 	bufs = kcalloc(nr_slots, sizeof(*bufs),
 		       GFP_KERNEL_ACCOUNT | __GFP_NOWARN);
-	if (unlikely(!bufs)) {
-		ret = -ENOMEM;
-		goto out_revert_acct;
-	}
+	if (unlikely(!bufs))
+		return -ENOMEM;
 
 	/*
 	 * The pipe array wraps around, so just start the new one at zero
···
 	kfree(pipe->bufs);
 	pipe->bufs = bufs;
 	pipe->ring_size = nr_slots;
-	pipe->max_usage = nr_slots;
+	if (pipe->max_usage > nr_slots)
+		pipe->max_usage = nr_slots;
 	pipe->tail = tail;
 	pipe->head = head;
 
 	/* This might have made more room for writers */
 	wake_up_interruptible(&pipe->wr_wait);
+	return 0;
+}
+
+/*
+ * Allocate a new array of pipe buffers and copy the info over. Returns the
+ * pipe size if successful, or return -ERROR on error.
+ */
+static long pipe_set_size(struct pipe_inode_info *pipe, unsigned long arg)
+{
+	unsigned long user_bufs;
+	unsigned int nr_slots, size;
+	long ret = 0;
+
+#ifdef CONFIG_WATCH_QUEUE
+	if (pipe->watch_queue)
+		return -EBUSY;
+#endif
+
+	size = round_pipe_size(arg);
+	nr_slots = size >> PAGE_SHIFT;
+
+	if (!nr_slots)
+		return -EINVAL;
+
+	/*
+	 * If trying to increase the pipe capacity, check that an
+	 * unprivileged user is not trying to exceed various limits
+	 * (soft limit check here, hard limit check just below).
+	 * Decreasing the pipe capacity is always permitted, even
+	 * if the user is currently over a limit.
+	 */
+	if (nr_slots > pipe->max_usage &&
+			size > pipe_max_size && !capable(CAP_SYS_RESOURCE))
+		return -EPERM;
+
+	user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_slots);
+
+	if (nr_slots > pipe->max_usage &&
+			(too_many_pipe_buffers_hard(user_bufs) ||
+			 too_many_pipe_buffers_soft(user_bufs)) &&
+			pipe_is_unprivileged_user()) {
+		ret = -EPERM;
+		goto out_revert_acct;
+	}
+
+	ret = pipe_resize_ring(pipe, nr_slots);
+	if (ret < 0)
+		goto out_revert_acct;
+
+	pipe->max_usage = nr_slots;
+	pipe->nr_accounted = nr_slots;
 	return pipe->max_usage * PAGE_SIZE;
 
 out_revert_acct:
-	(void) account_pipe_buffers(pipe->user, nr_slots, pipe->ring_size);
+	(void) account_pipe_buffers(pipe->user, nr_slots, pipe->nr_accounted);
 	return ret;
 }
 
···
  * location, so checking ->i_pipe is not enough to verify that this is a
  * pipe.
  */
-struct pipe_inode_info *get_pipe_info(struct file *file)
+struct pipe_inode_info *get_pipe_info(struct file *file, bool for_splice)
 {
-	return file->f_op == &pipefifo_fops ? file->private_data : NULL;
+	struct pipe_inode_info *pipe = file->private_data;
+
+	if (file->f_op != &pipefifo_fops || !pipe)
+		return NULL;
+#ifdef CONFIG_WATCH_QUEUE
+	if (for_splice && pipe->watch_queue)
+		return NULL;
+#endif
+	return pipe;
 }
 
 long pipe_fcntl(struct file *file, unsigned int cmd, unsigned long arg)
···
 	struct pipe_inode_info *pipe;
 	long ret;
 
-	pipe = get_pipe_info(file);
+	pipe = get_pipe_info(file, false);
 	if (!pipe)
 		return -EBADF;
 

fs/splice.c

···
 		     !(out->f_mode & FMODE_WRITE)))
 		return -EBADF;
 
-	ipipe = get_pipe_info(in);
-	opipe = get_pipe_info(out);
+	ipipe = get_pipe_info(in, true);
+	opipe = get_pipe_info(out, true);
 
 	if (ipipe && opipe) {
 		if (off_in || off_out)
···
 static long vmsplice_to_user(struct file *file, struct iov_iter *iter,
 			     unsigned int flags)
 {
-	struct pipe_inode_info *pipe = get_pipe_info(file);
+	struct pipe_inode_info *pipe = get_pipe_info(file, true);
 	struct splice_desc sd = {
 		.total_len = iov_iter_count(iter),
 		.flags = flags,
···
 	if (flags & SPLICE_F_GIFT)
 		buf_flag = PIPE_BUF_FLAG_GIFT;
 
-	pipe = get_pipe_info(file);
+	pipe = get_pipe_info(file, true);
 	if (!pipe)
 		return -EBADF;
 
···
  */
 long do_tee(struct file *in, struct file *out, size_t len, unsigned int flags)
 {
-	struct pipe_inode_info *ipipe = get_pipe_info(in);
-	struct pipe_inode_info *opipe = get_pipe_info(out);
+	struct pipe_inode_info *ipipe = get_pipe_info(in, true);
+	struct pipe_inode_info *opipe = get_pipe_info(out, true);
 	int ret = -EINVAL;
 
 	if (unlikely(!(in->f_mode & FMODE_READ) ||

include/linux/key.h

···
 
 #define KEY_PERM_UNDEF	0xffffffff
 
+/*
+ * The permissions required on a key that we're looking up.
+ */
+enum key_need_perm {
+	KEY_NEED_UNSPECIFIED,	/* Needed permission unspecified */
+	KEY_NEED_VIEW,		/* Require permission to view attributes */
+	KEY_NEED_READ,		/* Require permission to read content */
+	KEY_NEED_WRITE,		/* Require permission to update / modify */
+	KEY_NEED_SEARCH,	/* Require permission to search (keyring) or find (key) */
+	KEY_NEED_LINK,		/* Require permission to link */
+	KEY_NEED_SETATTR,	/* Require permission to change attributes */
+	KEY_NEED_UNLINK,	/* Require permission to unlink key */
+	KEY_SYSADMIN_OVERRIDE,	/* Special: override by CAP_SYS_ADMIN */
+	KEY_AUTHTOKEN_OVERRIDE,	/* Special: override by possession of auth token */
+	KEY_DEFER_PERM_CHECK,	/* Special: permission check is deferred */
+};
+
 struct seq_file;
 struct user_struct;
 struct signal_struct;
···
 		struct list_head graveyard_link;
 		struct rb_node	serial_node;
 	};
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	struct watch_list	*watchers;	/* Entities watching this key for changes */
+#endif
 	struct rw_semaphore	sem;		/* change vs change sem */
 	struct key_user		*user;		/* owner of this key */
 	void			*security;	/* security data for this key */
···
 extern void key_set_timeout(struct key *, unsigned);
 
 extern key_ref_t lookup_user_key(key_serial_t id, unsigned long flags,
-				 key_perm_t perm);
+				 enum key_need_perm need_perm);
 extern void key_free_user_ns(struct user_namespace *);
-
-/*
- * The permissions required on a key that we're looking up.
- */
-#define	KEY_NEED_VIEW	0x01	/* Require permission to view attributes */
-#define	KEY_NEED_READ	0x02	/* Require permission to read content */
-#define	KEY_NEED_WRITE	0x04	/* Require permission to update / modify */
-#define	KEY_NEED_SEARCH	0x08	/* Require permission to search (keyring) or find (key) */
-#define	KEY_NEED_LINK	0x10	/* Require permission to link */
-#define	KEY_NEED_SETATTR 0x20	/* Require permission to change attributes */
-#define	KEY_NEED_ALL	0x3f	/* All the above permissions */
 
 static inline short key_read_state(const struct key *key)
 {

include/linux/lsm_audit.h

···
 #define LSM_AUDIT_DATA_IBPKEY	13
 #define LSM_AUDIT_DATA_IBENDPORT 14
 #define LSM_AUDIT_DATA_LOCKDOWN 15
+#define LSM_AUDIT_DATA_NOTIFICATION 16
 	union 	{
 		struct path path;
 		struct dentry *dentry;

include/linux/lsm_hook_defs.h

···
 LSM_HOOK(int, 0, inode_getsecctx, struct inode *inode, void **ctx,
 	 u32 *ctxlen)
 
+#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
+LSM_HOOK(int, 0, post_notification, const struct cred *w_cred,
+	 const struct cred *cred, struct watch_notification *n)
+#endif /* CONFIG_SECURITY && CONFIG_WATCH_QUEUE */
+
+#if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
+LSM_HOOK(int, 0, watch_key, struct key *key)
+#endif /* CONFIG_SECURITY && CONFIG_KEY_NOTIFICATIONS */
+
 #ifdef CONFIG_SECURITY_NETWORK
 LSM_HOOK(int, 0, unix_stream_connect, struct sock *sock, struct sock *other,
 	 struct sock *newsk)

include/linux/lsm_hooks.h

···
  *	@ctx is a pointer in which to place the allocated security context.
  *	@ctxlen points to the place to put the length of @ctx.
  *
+ * Security hooks for the general notification queue:
+ *
+ * @post_notification:
+ *	Check to see if a watch notification can be posted to a particular
+ *	queue.
+ *	@w_cred: The credentials of the whoever set the watch.
+ *	@cred: The event-triggerer's credentials
+ *	@n: The notification being posted
+ *
+ * @watch_key:
+ *	Check to see if a process is allowed to watch for event notifications
+ *	from a key or keyring.
+ *	@key: The key to watch.
+ *
  * Security hooks for using the eBPF maps and programs functionalities through
  * eBPF syscalls.
  *

include/linux/pipe_fs_i.h

···
 #define PIPE_BUF_FLAG_GIFT	0x04	/* page is a gift */
 #define PIPE_BUF_FLAG_PACKET	0x08	/* read() as a packet */
 #define PIPE_BUF_FLAG_CAN_MERGE	0x10	/* can merge buffers */
+#define PIPE_BUF_FLAG_WHOLE	0x20	/* read() must return entire buffer or error */
+#ifdef CONFIG_WATCH_QUEUE
+#define PIPE_BUF_FLAG_LOSS	0x40	/* Message loss happened after this buffer */
+#endif
 
 /**
  *	struct pipe_buffer - a linux kernel pipe buffer
···
  *	@wr_wait: writer wait point in case of full pipe
  *	@head: The point of buffer production
  *	@tail: The point of buffer consumption
+ *	@note_loss: The next read() should insert a data-lost message
  *	@max_usage: The maximum number of slots that may be used in the ring
  *	@ring_size: total number of buffers (should be a power of 2)
+ *	@nr_accounted: The amount this pipe accounts for in user->pipe_bufs
  *	@tmp_page: cached released page
  *	@readers: number of current readers of this pipe
  *	@writers: number of current writers of this pipe
···
  *	@fasync_writers: writer side fasync
  *	@bufs: the circular array of pipe buffers
  *	@user: the user who created this pipe
+ *	@watch_queue: If this pipe is a watch_queue, this is the stuff for that
  **/
 struct pipe_inode_info {
 	struct mutex mutex;
···
 	unsigned int tail;
 	unsigned int max_usage;
 	unsigned int ring_size;
+#ifdef CONFIG_WATCH_QUEUE
+	bool note_loss;
+#endif
+	unsigned int nr_accounted;
 	unsigned int readers;
 	unsigned int writers;
 	unsigned int files;
···
 	struct fasync_struct *fasync_writers;
 	struct pipe_buffer *bufs;
 	struct user_struct *user;
+#ifdef CONFIG_WATCH_QUEUE
+	struct watch_queue *watch_queue;
+#endif
 };
 
 /*
···
 
 extern const struct pipe_buf_operations nosteal_pipe_buf_ops;
 
+#ifdef CONFIG_WATCH_QUEUE
+unsigned long account_pipe_buffers(struct user_struct *user,
+				   unsigned long old, unsigned long new);
+bool too_many_pipe_buffers_soft(unsigned long user_bufs);
+bool too_many_pipe_buffers_hard(unsigned long user_bufs);
+bool pipe_is_unprivileged_user(void);
+#endif
+
 /* for F_SETPIPE_SZ and F_GETPIPE_SZ */
+#ifdef CONFIG_WATCH_QUEUE
+int pipe_resize_ring(struct pipe_inode_info *pipe, unsigned int nr_slots);
+#endif
 long pipe_fcntl(struct file *, unsigned int, unsigned long arg);
-struct pipe_inode_info *get_pipe_info(struct file *file);
+struct pipe_inode_info *get_pipe_info(struct file *file, bool for_splice);
 
 int create_pipe_files(struct file **, int);
 unsigned int round_pipe_size(unsigned long size);

include/linux/security.h

···
 struct fs_context;
 struct fs_parameter;
 enum fs_value_type;
+struct watch;
+struct watch_notification;
 
 /* Default (no) options for the capable function */
 #define CAP_OPT_NONE 0x0
···
 }
 #endif	/* CONFIG_SECURITY */
 
+#if defined(CONFIG_SECURITY) && defined(CONFIG_WATCH_QUEUE)
+int security_post_notification(const struct cred *w_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n);
+#else
+static inline int security_post_notification(const struct cred *w_cred,
+					     const struct cred *cred,
+					     struct watch_notification *n)
+{
+	return 0;
+}
+#endif
+
+#if defined(CONFIG_SECURITY) && defined(CONFIG_KEY_NOTIFICATIONS)
+int security_watch_key(struct key *key);
+#else
+static inline int security_watch_key(struct key *key)
+{
+	return 0;
+}
+#endif
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk);
···
 
 int security_key_alloc(struct key *key, const struct cred *cred, unsigned long flags);
 void security_key_free(struct key *key);
-int security_key_permission(key_ref_t key_ref,
-			    const struct cred *cred, unsigned perm);
+int security_key_permission(key_ref_t key_ref, const struct cred *cred,
+			    enum key_need_perm need_perm);
 int security_key_getsecurity(struct key *key, char **_buffer);
 
 #else
···
 
 static inline int security_key_permission(key_ref_t key_ref,
 					  const struct cred *cred,
-					  unsigned perm)
+					  enum key_need_perm need_perm)
 {
 	return 0;
 }

include/linux/watch_queue.h

···
+// SPDX-License-Identifier: GPL-2.0
+/* User-mappable watch queue
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ *
+ * See Documentation/watch_queue.rst
+ */
+
+#ifndef _LINUX_WATCH_QUEUE_H
+#define _LINUX_WATCH_QUEUE_H
+
+#include <uapi/linux/watch_queue.h>
+#include <linux/kref.h>
+#include <linux/rcupdate.h>
+
+#ifdef CONFIG_WATCH_QUEUE
+
+struct cred;
+
+struct watch_type_filter {
+	enum watch_notification_type type;
+	__u32		subtype_filter[1];	/* Bitmask of subtypes to filter on */
+	__u32		info_filter;		/* Filter on watch_notification::info */
+	__u32		info_mask;		/* Mask of relevant bits in info_filter */
+};
+
+struct watch_filter {
+	union {
+		struct rcu_head	rcu;
+		unsigned long	type_filter[2];	/* Bitmask of accepted types */
+	};
+	u32			nr_filters;	/* Number of filters */
+	struct watch_type_filter filters[];
+};
+
+struct watch_queue {
+	struct rcu_head		rcu;
+	struct watch_filter __rcu *filter;
+	struct pipe_inode_info	*pipe;		/* The pipe we're using as a buffer */
+	struct hlist_head	watches;	/* Contributory watches */
+	struct page		**notes;	/* Preallocated notifications */
+	unsigned long		*notes_bitmap;	/* Allocation bitmap for notes */
+	struct kref		usage;		/* Object usage count */
+	spinlock_t		lock;
+	unsigned int		nr_notes;	/* Number of notes */
+	unsigned int		nr_pages;	/* Number of pages in notes[] */
+	bool			defunct;	/* T when queues closed */
+};
+
+/*
+ * Representation of a watch on an object.
+ */
+struct watch {
+	union {
+		struct rcu_head	rcu;
+		u32		info_id;	/* ID to be OR'd in to info field */
+	};
+	struct watch_queue __rcu *queue;	/* Queue to post events to */
+	struct hlist_node	queue_node;	/* Link in queue->watches */
+	struct watch_list __rcu	*watch_list;
+	struct hlist_node	list_node;	/* Link in watch_list->watchers */
+	const struct cred	*cred;		/* Creds of the owner of the watch */
+	void			*private;	/* Private data for the watched object */
+	u64			id;		/* Internal identifier */
+	struct kref		usage;		/* Object usage count */
+};
+
+/*
+ * List of watches on an object.
+ */
+struct watch_list {
+	struct rcu_head		rcu;
+	struct hlist_head	watchers;
+	void (*release_watch)(struct watch *);
+	spinlock_t		lock;
+};
+
+extern void __post_watch_notification(struct watch_list *,
+				      struct watch_notification *,
+				      const struct cred *,
+				      u64);
+extern struct watch_queue *get_watch_queue(int);
+extern void put_watch_queue(struct watch_queue *);
+extern void init_watch(struct watch *, struct watch_queue *);
+extern int add_watch_to_object(struct watch *, struct watch_list *);
+extern int remove_watch_from_object(struct watch_list *, struct watch_queue *, u64, bool);
+extern long watch_queue_set_size(struct pipe_inode_info *, unsigned int);
+extern long watch_queue_set_filter(struct pipe_inode_info *,
+				   struct watch_notification_filter __user *);
+extern int watch_queue_init(struct pipe_inode_info *);
+extern void watch_queue_clear(struct watch_queue *);
+
+static inline void init_watch_list(struct watch_list *wlist,
+				   void (*release_watch)(struct watch *))
+{
+	INIT_HLIST_HEAD(&wlist->watchers);
+	spin_lock_init(&wlist->lock);
+	wlist->release_watch = release_watch;
+}
+
+static inline void post_watch_notification(struct watch_list *wlist,
+					   struct watch_notification *n,
+					   const struct cred *cred,
+					   u64 id)
+{
+	if (unlikely(wlist))
+		__post_watch_notification(wlist, n, cred, id);
+}
+
+static inline void remove_watch_list(struct watch_list *wlist, u64 id)
+{
+	if (wlist) {
+		remove_watch_from_object(wlist, NULL, id, true);
+		kfree_rcu(wlist, rcu);
+	}
+}
+
+/**
+ * watch_sizeof - Calculate the information part of the size of a watch record,
+ * given the structure size.
+ */
+#define watch_sizeof(STRUCT) (sizeof(STRUCT) << WATCH_INFO_LENGTH__SHIFT)
+
+#endif
+
+#endif /* _LINUX_WATCH_QUEUE_H */

include/uapi/linux/keyctl.h

···
 #define KEYCTL_RESTRICT_KEYRING		29	/* Restrict keys allowed to link to a keyring */
 #define KEYCTL_MOVE			30	/* Move keys between keyrings */
 #define KEYCTL_CAPABILITIES		31	/* Find capabilities of keyrings subsystem */
+#define KEYCTL_WATCH_KEY		32	/* Watch a key or ring of keys for changes */
 
 /* keyctl structures */
 struct keyctl_dh_params {
···
 #define KEYCTL_CAPS0_MOVE		0x80 /* KEYCTL_MOVE supported */
 #define KEYCTL_CAPS1_NS_KEYRING_NAME	0x01 /* Keyring names are per-user_namespace */
 #define KEYCTL_CAPS1_NS_KEY_TAG		0x02 /* Key indexing can include a namespace tag */
+#define KEYCTL_CAPS1_NOTIFICATIONS	0x04 /* Keys generate watchable notifications */
 
 #endif /*  _LINUX_KEYCTL_H */

include/uapi/linux/watch_queue.h

···
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _UAPI_LINUX_WATCH_QUEUE_H
+#define _UAPI_LINUX_WATCH_QUEUE_H
+
+#include <linux/types.h>
+#include <linux/fcntl.h>
+#include <linux/ioctl.h>
+
+#define O_NOTIFICATION_PIPE	O_EXCL	/* Parameter to pipe2() selecting notification pipe */
+
+#define IOC_WATCH_QUEUE_SET_SIZE	_IO('W', 0x60)	/* Set the size in pages */
+#define IOC_WATCH_QUEUE_SET_FILTER	_IO('W', 0x61)	/* Set the filter */
+
+enum watch_notification_type {
+	WATCH_TYPE_META		= 0,	/* Special record */
+	WATCH_TYPE_KEY_NOTIFY	= 1,	/* Key change event notification */
+	WATCH_TYPE__NR		= 2
+};
+
+enum watch_meta_notification_subtype {
+	WATCH_META_REMOVAL_NOTIFICATION	= 0,	/* Watched object was removed */
+	WATCH_META_LOSS_NOTIFICATION	= 1,	/* Data loss occurred */
+};
+
+/*
+ * Notification record header.  This is aligned to 64-bits so that subclasses
+ * can contain __u64 fields.
+ */
+struct watch_notification {
+	__u32			type:24;	/* enum watch_notification_type */
+	__u32			subtype:8;	/* Type-specific subtype (filterable) */
+	__u32			info;
+#define WATCH_INFO_LENGTH	0x0000007f	/* Length of record */
+#define WATCH_INFO_LENGTH__SHIFT 0
+#define WATCH_INFO_ID		0x0000ff00	/* ID of watchpoint */
+#define WATCH_INFO_ID__SHIFT	8
+#define WATCH_INFO_TYPE_INFO	0xffff0000	/* Type-specific info */
+#define WATCH_INFO_TYPE_INFO__SHIFT 16
+#define WATCH_INFO_FLAG_0	0x00010000	/* Type-specific info, flag bit 0 */
+#define WATCH_INFO_FLAG_1	0x00020000	/* ... */
+#define WATCH_INFO_FLAG_2	0x00040000
+#define WATCH_INFO_FLAG_3	0x00080000
+#define WATCH_INFO_FLAG_4	0x00100000
+#define WATCH_INFO_FLAG_5	0x00200000
+#define WATCH_INFO_FLAG_6	0x00400000
+#define WATCH_INFO_FLAG_7	0x00800000
+};
+
+/*
+ * Notification filtering rules (IOC_WATCH_QUEUE_SET_FILTER).
+ */
+struct watch_notification_type_filter {
+	__u32	type;			/* Type to apply filter to */
+	__u32	info_filter;		/* Filter on watch_notification::info */
+	__u32	info_mask;		/* Mask of relevant bits in info_filter */
+	__u32	subtype_filter[8];	/* Bitmask of subtypes to filter on */
+};
+
+struct watch_notification_filter {
+	__u32	nr_filters;		/* Number of filters */
+	__u32	__reserved;		/* Must be 0 */
+	struct watch_notification_type_filter filters[];
+};
+
+
+/*
+ * Extended watch removal notification.  This is used optionally if the type
+ * wants to indicate an identifier for the object being watched, if there is
+ * such.  This can be distinguished by the length.
+ *
+ * type -> WATCH_TYPE_META
+ * subtype -> WATCH_META_REMOVAL_NOTIFICATION
+ */
+struct watch_notification_removal {
+	struct watch_notification watch;
+	__u64	id;		/* Type-dependent identifier */
+};
+
+/*
+ * Type of key/keyring change notification.
+ */
+enum key_notification_subtype {
+	NOTIFY_KEY_INSTANTIATED	= 0, /* Key was instantiated (aux is error code) */
+	NOTIFY_KEY_UPDATED	= 1, /* Key was updated */
+	NOTIFY_KEY_LINKED	= 2, /* Key (aux) was added to watched keyring */
+	NOTIFY_KEY_UNLINKED	= 3, /* Key (aux) was removed from watched keyring */
+	NOTIFY_KEY_CLEARED	= 4, /* Keyring was cleared */
+	NOTIFY_KEY_REVOKED	= 5, /* Key was revoked */
+	NOTIFY_KEY_INVALIDATED	= 6, /* Key was invalidated */
+	NOTIFY_KEY_SETATTR	= 7, /* Key's attributes got changed */
+};
+
+/*
+ * Key/keyring notification record.
+ * - watch.type = WATCH_TYPE_KEY_NOTIFY
+ * - watch.subtype = enum key_notification_type
+ */
+struct key_notification {
+	struct watch_notification watch;
+	__u32	key_id;		/* The key/keyring affected */
+	__u32	aux;		/* Per-type auxiliary data */
+};
+
+#endif /* _UAPI_LINUX_WATCH_QUEUE_H */

init/Kconfig

···
 	depends on SYSCTL
 	default y
 
+config WATCH_QUEUE
+	bool "General notification queue"
+	default n
+	help
+
+	  This is a general notification queue for the kernel to pass events to
+	  userspace by splicing them into pipes.  It can be used in conjunction
+	  with watches for key/keyring change notifications and device
+	  notifications.
+
+	  See Documentation/watch_queue.rst
+
 config CROSS_MEMORY_ATTACH
 	bool "Enable process_vm_readv/writev syscalls"
 	depends on MMU

kernel/Makefile

···
 
 obj-$(CONFIG_HAS_IOMEM) += iomem.o
 obj-$(CONFIG_RSEQ) += rseq.o
+obj-$(CONFIG_WATCH_QUEUE) += watch_queue.o
 
 obj-$(CONFIG_SYSCTL_KUNIT_TEST) += sysctl-test.o
 

kernel/watch_queue.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Watch queue and general notification mechanism, built on pipes
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ *
+ * See Documentation/watch_queue.rst
+ */
+
+#define pr_fmt(fmt) "watchq: " fmt
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/printk.h>
+#include <linux/miscdevice.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+#include <linux/pagemap.h>
+#include <linux/poll.h>
+#include <linux/uaccess.h>
+#include <linux/vmalloc.h>
+#include <linux/file.h>
+#include <linux/security.h>
+#include <linux/cred.h>
+#include <linux/sched/signal.h>
+#include <linux/watch_queue.h>
+#include <linux/pipe_fs_i.h>
+
+MODULE_DESCRIPTION("Watch queue");
+MODULE_AUTHOR("Red Hat, Inc.");
+MODULE_LICENSE("GPL");
+
+#define WATCH_QUEUE_NOTE_SIZE 128
+#define WATCH_QUEUE_NOTES_PER_PAGE (PAGE_SIZE / WATCH_QUEUE_NOTE_SIZE)
+
+static void watch_queue_pipe_buf_release(struct pipe_inode_info *pipe,
+					 struct pipe_buffer *buf)
+{
+	struct watch_queue *wqueue = (struct watch_queue *)buf->private;
+	struct page *page;
+	unsigned int bit;
+
+	/* We need to work out which note within the page this refers to, but
+	 * the note might have been maximum size, so merely ANDing the offset
+	 * off doesn't work.  OTOH, the note must've been more than zero size.
+	 */
+	bit = buf->offset + buf->len;
+	if ((bit & (WATCH_QUEUE_NOTE_SIZE - 1)) == 0)
+		bit -= WATCH_QUEUE_NOTE_SIZE;
+	bit /= WATCH_QUEUE_NOTE_SIZE;
+
+	page = buf->page;
+	bit += page->index;
+
+	set_bit(bit, wqueue->notes_bitmap);
+}
+
+// No try_steal function => no stealing
+#define watch_queue_pipe_buf_try_steal NULL
+
+/* New data written to a pipe may be appended to a buffer with this type. */
+static const struct pipe_buf_operations watch_queue_pipe_buf_ops = {
+	.release	= watch_queue_pipe_buf_release,
+	.try_steal	= watch_queue_pipe_buf_try_steal,
+	.get		= generic_pipe_buf_get,
+};
+
+/*
+ * Post a notification to a watch queue.
+ */
+static bool post_one_notification(struct watch_queue *wqueue,
+				  struct watch_notification *n)
+{
+	void *p;
+	struct pipe_inode_info *pipe = wqueue->pipe;
+	struct pipe_buffer *buf;
+	struct page *page;
+	unsigned int head, tail, mask, note, offset, len;
+	bool done = false;
+
+	if (!pipe)
+		return false;
+
+	spin_lock_irq(&pipe->rd_wait.lock);
+
+	if (wqueue->defunct)
+		goto out;
+
+	mask = pipe->ring_size - 1;
+	head = pipe->head;
+	tail = pipe->tail;
+	if (pipe_full(head, tail, pipe->ring_size))
+		goto lost;
+
+	note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
+	if (note >= wqueue->nr_notes)
+		goto lost;
+
+	page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
+	offset = note % WATCH_QUEUE_NOTES_PER_PAGE * WATCH_QUEUE_NOTE_SIZE;
+	get_page(page);
+	len = n->info & WATCH_INFO_LENGTH;
+	p = kmap_atomic(page);
+	memcpy(p + offset, n, len);
+	kunmap_atomic(p);
+
+	buf = &pipe->bufs[head & mask];
+	buf->page = page;
+	buf->private = (unsigned long)wqueue;
+	buf->ops = &watch_queue_pipe_buf_ops;
+	buf->offset = offset;
+	buf->len = len;
+	buf->flags = PIPE_BUF_FLAG_WHOLE;
+	pipe->head = head + 1;
+
+	if (!test_and_clear_bit(note, wqueue->notes_bitmap)) {
+		spin_unlock_irq(&pipe->rd_wait.lock);
+		BUG();
+	}
+	wake_up_interruptible_sync_poll_locked(&pipe->rd_wait, EPOLLIN | EPOLLRDNORM);
+	done = true;
+
+out:
+	spin_unlock_irq(&pipe->rd_wait.lock);
+	if (done)
+		kill_fasync(&pipe->fasync_readers, SIGIO, POLL_IN);
+	return done;
+
+lost:
+	buf = &pipe->bufs[(head - 1) & mask];
+	buf->flags |= PIPE_BUF_FLAG_LOSS;
+	goto out;
+}
+
+/*
+ * Apply filter rules to a notification.
+ */
+static bool filter_watch_notification(const struct watch_filter *wf,
+				      const struct watch_notification *n)
+{
+	const struct watch_type_filter *wt;
+	unsigned int st_bits = sizeof(wt->subtype_filter[0]) * 8;
+	unsigned int st_index = n->subtype / st_bits;
+	unsigned int st_bit = 1U << (n->subtype % st_bits);
+	int i;
+
+	if (!test_bit(n->type, wf->type_filter))
+		return false;
+
+	for (i = 0; i < wf->nr_filters; i++) {
+		wt = &wf->filters[i];
+		if (n->type == wt->type &&
+		    (wt->subtype_filter[st_index] & st_bit) &&
+		    (n->info & wt->info_mask) == wt->info_filter)
+			return true;
+	}
+
+	return false; /* If there is a filter, the default is to reject. */
+}
+
+/**
+ * __post_watch_notification - Post an event notification
+ * @wlist: The watch list to post the event to.
+ * @n: The notification record to post.
+ * @cred: The creds of the process that triggered the notification.
+ * @id: The ID to match on the watch.
+ *
+ * Post a notification of an event into a set of watch queues and let the users
+ * know.
+ *
+ * The size of the notification should be set in n->info & WATCH_INFO_LENGTH and
+ * should be in units of sizeof(*n).
+ */
+void __post_watch_notification(struct watch_list *wlist,
+			       struct watch_notification *n,
+			       const struct cred *cred,
+			       u64 id)
+{
+	const struct watch_filter *wf;
+	struct watch_queue *wqueue;
+	struct watch *watch;
+
+	if (((n->info & WATCH_INFO_LENGTH) >> WATCH_INFO_LENGTH__SHIFT) == 0) {
+		WARN_ON(1);
+		return;
+	}
+
+	rcu_read_lock();
+
+	hlist_for_each_entry_rcu(watch, &wlist->watchers, list_node) {
+		if (watch->id != id)
+			continue;
+		n->info &= ~WATCH_INFO_ID;
+		n->info |= watch->info_id;
+
+		wqueue = rcu_dereference(watch->queue);
+		wf = rcu_dereference(wqueue->filter);
+		if (wf && !filter_watch_notification(wf, n))
+			continue;
+
+		if (security_post_notification(watch->cred, cred, n) < 0)
+			continue;
+
+		post_one_notification(wqueue, n);
+	}
+
+	rcu_read_unlock();
+}
+EXPORT_SYMBOL(__post_watch_notification);
+
+/*
+ * Allocate sufficient pages to preallocation for the requested number of
+ * notifications.
+ */
+long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
+{
+	struct watch_queue *wqueue = pipe->watch_queue;
+	struct page **pages;
+	unsigned long *bitmap;
+	unsigned long user_bufs;
+	unsigned int bmsize;
+	int ret, i, nr_pages;
+
+	if (!wqueue)
+		return -ENODEV;
+	if (wqueue->notes)
+		return -EBUSY;
+
+	if (nr_notes < 1 ||
+	    nr_notes > 512) /* TODO: choose a better hard limit */
+		return -EINVAL;
+
+	nr_pages = (nr_notes + WATCH_QUEUE_NOTES_PER_PAGE - 1);
+	nr_pages /= WATCH_QUEUE_NOTES_PER_PAGE;
+	user_bufs = account_pipe_buffers(pipe->user, pipe->nr_accounted, nr_pages);
+
+	if (nr_pages > pipe->max_usage &&
+	    (too_many_pipe_buffers_hard(user_bufs) ||
+	     too_many_pipe_buffers_soft(user_bufs)) &&
+	    pipe_is_unprivileged_user()) {
+		ret = -EPERM;
+		goto error;
+	}
+
+	ret = pipe_resize_ring(pipe, nr_notes);
+	if (ret < 0)
+		goto error;
+
+	pages = kcalloc(sizeof(struct page *), nr_pages, GFP_KERNEL);
+	if (!pages)
+		goto error;
+
+	for (i = 0; i < nr_pages; i++) {
+		pages[i] = alloc_page(GFP_KERNEL);
+		if (!pages[i])
+			goto error_p;
+		pages[i]->index = i * WATCH_QUEUE_NOTES_PER_PAGE;
+	}
+
+	bmsize = (nr_notes + BITS_PER_LONG - 1) / BITS_PER_LONG;
+	bmsize *= sizeof(unsigned long);
+	bitmap = kmalloc(bmsize, GFP_KERNEL);
+	if (!bitmap)
+		goto error_p;
+
+	memset(bitmap, 0xff, bmsize);
+	wqueue->notes = pages;
+	wqueue->notes_bitmap = bitmap;
+	wqueue->nr_pages = nr_pages;
+	wqueue->nr_notes = nr_pages * WATCH_QUEUE_NOTES_PER_PAGE;
+	return 0;
+
+error_p:
+	for (i = 0; i < nr_pages; i++)
+		__free_page(pages[i]);
+	kfree(pages);
+error:
+	(void) account_pipe_buffers(pipe->user, nr_pages, pipe->nr_accounted);
+	return ret;
+}
+
+/*
+ * Set the filter on a watch queue.
+ */
+long watch_queue_set_filter(struct pipe_inode_info *pipe,
+			    struct watch_notification_filter __user *_filter)
+{
+	struct watch_notification_type_filter *tf;
+	struct watch_notification_filter filter;
+	struct watch_type_filter *q;
+	struct watch_filter *wfilter;
+	struct watch_queue *wqueue = pipe->watch_queue;
+	int ret, nr_filter = 0, i;
+
+	if (!wqueue)
+		return -ENODEV;
+
+	if (!_filter) {
+		/* Remove the old filter */
+		wfilter = NULL;
+		goto set;
+	}
+
+	/* Grab the user's filter specification */
+	if (copy_from_user(&filter, _filter, sizeof(filter)) != 0)
+		return -EFAULT;
+	if (filter.nr_filters == 0 ||
+	    filter.nr_filters > 16 ||
+	    filter.__reserved != 0)
+		return -EINVAL;
+
+	tf = memdup_user(_filter->filters, filter.nr_filters * sizeof(*tf));
+	if (IS_ERR(tf))
+		return PTR_ERR(tf);
+
+	ret = -EINVAL;
+	for (i = 0; i < filter.nr_filters; i++) {
+		if ((tf[i].info_filter & ~tf[i].info_mask) ||
+		    tf[i].info_mask & WATCH_INFO_LENGTH)
+			goto err_filter;
+		/* Ignore any unknown types */
+		if (tf[i].type >= sizeof(wfilter->type_filter) * 8)
+			continue;
+		nr_filter++;
+	}
+
+	/* Now we need to build the internal filter from only the relevant
+	 * user-specified filters.
+	 */
+	ret = -ENOMEM;
+	wfilter = kzalloc(struct_size(wfilter, filters, nr_filter), GFP_KERNEL);
+	if (!wfilter)
+		goto err_filter;
+	wfilter->nr_filters = nr_filter;
+
+	q = wfilter->filters;
+	for (i = 0; i < filter.nr_filters; i++) {
+		if (tf[i].type >= sizeof(wfilter->type_filter) * BITS_PER_LONG)
+			continue;
+
+		q->type			= tf[i].type;
+		q->info_filter		= tf[i].info_filter;
+		q->info_mask		= tf[i].info_mask;
+		q->subtype_filter[0]	= tf[i].subtype_filter[0];
+		__set_bit(q->type, wfilter->type_filter);
+		q++;
+	}
+
+	kfree(tf);
+set:
+	pipe_lock(pipe);
+	wfilter = rcu_replace_pointer(wqueue->filter, wfilter,
+				      lockdep_is_held(&pipe->mutex));
+	pipe_unlock(pipe);
+	if (wfilter)
+		kfree_rcu(wfilter, rcu);
+	return 0;
+
+err_filter:
+	kfree(tf);
+	return ret;
+}
+
+static void __put_watch_queue(struct kref *kref)
+{
+	struct watch_queue *wqueue =
+		container_of(kref, struct watch_queue, usage);
+	struct watch_filter *wfilter;
+	int i;
+
+	for (i = 0; i < wqueue->nr_pages; i++)
+		__free_page(wqueue->notes[i]);
+
+	wfilter = rcu_access_pointer(wqueue->filter);
+	if (wfilter)
+		kfree_rcu(wfilter, rcu);
+	kfree_rcu(wqueue, rcu);
+}
+
+/**
+ * put_watch_queue - Dispose of a ref on a watchqueue.
+ * @wqueue: The watch queue to unref.
+ */
+void put_watch_queue(struct watch_queue *wqueue)
+{
+	kref_put(&wqueue->usage, __put_watch_queue);
+}
+EXPORT_SYMBOL(put_watch_queue);
+
+static void free_watch(struct rcu_head *rcu)
+{
+	struct watch *watch = container_of(rcu, struct watch, rcu);
+
+	put_watch_queue(rcu_access_pointer(watch->queue));
+	put_cred(watch->cred);
+}
+
+static void __put_watch(struct kref *kref)
+{
+	struct watch *watch = container_of(kref, struct watch, usage);
+
+	call_rcu(&watch->rcu, free_watch);
+}
+
+/*
+ * Discard a watch.
+ */
+static void put_watch(struct watch *watch)
+{
+	kref_put(&watch->usage, __put_watch);
+}
+
+/**
+ * init_watch_queue - Initialise a watch
+ * @watch: The watch to initialise.
+ * @wqueue: The queue to assign.
+ *
+ * Initialise a watch and set the watch queue.
+ */
+void init_watch(struct watch *watch, struct watch_queue *wqueue)
+{
+	kref_init(&watch->usage);
+	INIT_HLIST_NODE(&watch->list_node);
+	INIT_HLIST_NODE(&watch->queue_node);
+	rcu_assign_pointer(watch->queue, wqueue);
+}
+
+/**
+ * add_watch_to_object - Add a watch on an object to a watch list
+ * @watch: The watch to add
+ * @wlist: The watch list to add to
+ *
+ * @watch->queue must have been set to point to the queue to post notifications
+ * to and the watch list of the object to be watched.  @watch->cred must also
+ * have been set to the appropriate credentials and a ref taken on them.
+ *
+ * The caller must pin the queue and the list both and must hold the list
+ * locked against racing watch additions/removals.
+ */
+int add_watch_to_object(struct watch *watch, struct watch_list *wlist)
+{
+	struct watch_queue *wqueue = rcu_access_pointer(watch->queue);
+	struct watch *w;
+
+	hlist_for_each_entry(w, &wlist->watchers, list_node) {
+		struct watch_queue *wq = rcu_access_pointer(w->queue);
+		if (wqueue == wq && watch->id == w->id)
+			return -EBUSY;
+	}
+
+	watch->cred = get_current_cred();
+	rcu_assign_pointer(watch->watch_list, wlist);
+
+	spin_lock_bh(&wqueue->lock);
+	kref_get(&wqueue->usage);
+	kref_get(&watch->usage);
+	hlist_add_head(&watch->queue_node, &wqueue->watches);
+	spin_unlock_bh(&wqueue->lock);
+
+	hlist_add_head(&watch->list_node, &wlist->watchers);
+	return 0;
+}
+EXPORT_SYMBOL(add_watch_to_object);
+
+/**
+ * remove_watch_from_object - Remove a watch or all watches from an object.
+ * @wlist: The watch list to remove from
+ * @wq: The watch queue of interest (ignored if @all is true)
+ * @id: The ID of the watch to remove (ignored if @all is true)
+ * @all: True to remove all objects
+ *
+ * Remove a specific watch or all watches from an object.  A notification is
+ * sent to the watcher to tell them that this happened.
+ */
+int remove_watch_from_object(struct watch_list *wlist, struct watch_queue *wq,
+			     u64 id, bool all)
+{
+	struct watch_notification_removal n;
+	struct watch_queue *wqueue;
+	struct watch *watch;
+	int ret = -EBADSLT;
+
+	rcu_read_lock();
+
+again:
+	spin_lock(&wlist->lock);
+	hlist_for_each_entry(watch, &wlist->watchers, list_node) {
+		if (all ||
+		    (watch->id == id && rcu_access_pointer(watch->queue) == wq))
+			goto found;
+	}
+	spin_unlock(&wlist->lock);
+	goto out;
+
+found:
+	ret = 0;
+	hlist_del_init_rcu(&watch->list_node);
+	rcu_assign_pointer(watch->watch_list, NULL);
+	spin_unlock(&wlist->lock);
+
+	/* We now own the reference on watch that used to belong to wlist. */
+
+	n.watch.type = WATCH_TYPE_META;
+	n.watch.subtype = WATCH_META_REMOVAL_NOTIFICATION;
+	n.watch.info = watch->info_id | watch_sizeof(n.watch);
+	n.id = id;
+	if (id != 0)
+		n.watch.info = watch->info_id | watch_sizeof(n);
+
+	wqueue = rcu_dereference(watch->queue);
+
+	/* We don't need the watch list lock for the next bit as RCU is
+	 * protecting *wqueue from deallocation.
+	 */
+	if (wqueue) {
+		post_one_notification(wqueue, &n.watch);
+
+		spin_lock_bh(&wqueue->lock);
+
+		if (!hlist_unhashed(&watch->queue_node)) {
+			hlist_del_init_rcu(&watch->queue_node);
+			put_watch(watch);
+		}
+
+		spin_unlock_bh(&wqueue->lock);
+	}
+
+	if (wlist->release_watch) {
+		void (*release_watch)(struct watch *);
+
+		release_watch = wlist->release_watch;
+		rcu_read_unlock();
+		(*release_watch)(watch);
+		rcu_read_lock();
+	}
+	put_watch(watch);
+
+	if (all && !hlist_empty(&wlist->watchers))
+		goto again;
+out:
+	rcu_read_unlock();
+	return ret;
+}
+EXPORT_SYMBOL(remove_watch_from_object);
+
+/*
+ * Remove all the watches that are contributory to a queue.  This has the
+ * potential to race with removal of the watches by the destruction of the
+ * objects being watched or with the distribution of notifications.
+ */
+void watch_queue_clear(struct watch_queue *wqueue)
+{
+	struct watch_list *wlist;
+	struct watch *watch;
+	bool release;
+
+	rcu_read_lock();
+	spin_lock_bh(&wqueue->lock);
+
+	/* Prevent new additions and prevent notifications from happening */
+	wqueue->defunct = true;
+
+	while (!hlist_empty(&wqueue->watches)) {
+		watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);
+		hlist_del_init_rcu(&watch->queue_node);
+		/* We now own a ref on the watch. */
+		spin_unlock_bh(&wqueue->lock);
+
+		/* We can't do the next bit under the queue lock as we need to
+		 * get the list lock - which would cause a deadlock if someone
+		 * was removing from the opposite direction at the same time or
+		 * posting a notification.
+		 */
+		wlist = rcu_dereference(watch->watch_list);
+		if (wlist) {
+			void (*release_watch)(struct watch *);
+
+			spin_lock(&wlist->lock);
+
+			release = !hlist_unhashed(&watch->list_node);
+			if (release) {
+				hlist_del_init_rcu(&watch->list_node);
+				rcu_assign_pointer(watch->watch_list, NULL);
+
+				/* We now own a second ref on the watch. */
+			}
+
+			release_watch = wlist->release_watch;
+			spin_unlock(&wlist->lock);
+
+			if (release) {
+				if (release_watch) {
+					rcu_read_unlock();
+					/* This might need to call dput(), so
+					 * we have to drop all the locks.
+					 */
+					(*release_watch)(watch);
+					rcu_read_lock();
+				}
+				put_watch(watch);
+			}
+		}
+
+		put_watch(watch);
+		spin_lock_bh(&wqueue->lock);
+	}
+
+	spin_unlock_bh(&wqueue->lock);
+	rcu_read_unlock();
+}
+
+/**
+ * get_watch_queue - Get a watch queue from its file descriptor.
+ * @fd: The fd to query.
+ */
+struct watch_queue *get_watch_queue(int fd)
+{
+	struct pipe_inode_info *pipe;
+	struct watch_queue *wqueue = ERR_PTR(-EINVAL);
+	struct fd f;
+
+	f = fdget(fd);
+	if (f.file) {
+		pipe = get_pipe_info(f.file, false);
+		if (pipe && pipe->watch_queue) {
+			wqueue = pipe->watch_queue;
+			kref_get(&wqueue->usage);
+		}
+		fdput(f);
+	}
+
+	return wqueue;
+}
+EXPORT_SYMBOL(get_watch_queue);
+
+/*
+ * Initialise a watch queue
+ */
+int watch_queue_init(struct pipe_inode_info *pipe)
+{
+	struct watch_queue *wqueue;
+
+	wqueue = kzalloc(sizeof(*wqueue), GFP_KERNEL);
+	if (!wqueue)
+		return -ENOMEM;
+
+	wqueue->pipe = pipe;
+	kref_init(&wqueue->usage);
+	spin_lock_init(&wqueue->lock);
+	INIT_HLIST_HEAD(&wqueue->watches);
+
+	pipe->watch_queue = wqueue;
+	return 0;
+}

samples/Kconfig

···
 	bool "watchdog sample"
 	depends on CC_CAN_LINK
 
+config SAMPLE_WATCH_QUEUE
+	bool "Build example /dev/watch_queue notification consumer"
+	depends on HEADERS_INSTALL
+	help
+	  Build example userspace program to use the new mount_notify(),
+	  sb_notify() syscalls and the KEYCTL_WATCH_KEY keyctl() function.
+
 endif # SAMPLES

samples/Makefile

···
 subdir-$(CONFIG_SAMPLE_VFS)		+= vfs
 obj-$(CONFIG_SAMPLE_INTEL_MEI)		+= mei/
 subdir-$(CONFIG_SAMPLE_WATCHDOG)	+= watchdog
+subdir-$(CONFIG_SAMPLE_WATCH_QUEUE)	+= watch_queue

samples/watch_queue/Makefile

···
+# List of programs to build
+hostprogs := watch_test
+
+# Tell kbuild to always build the programs
+always-y := $(hostprogs)
+
+HOSTCFLAGS_watch_test.o += -I$(objtree)/usr/include

samples/watch_queue/watch_test.c

···
+// SPDX-License-Identifier: GPL-2.0
+/* Use /dev/watch_queue to watch for notifications.
+ *
+ * Copyright (C) 2020 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells ([e-mail])
+ */
+
+#define _GNU_SOURCE
+#include <stdbool.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+#include <unistd.h>
+#include <errno.h>
+#include <sys/ioctl.h>
+#include <limits.h>
+#include <linux/watch_queue.h>
+#include <linux/unistd.h>
+#include <linux/keyctl.h>
+
+#ifndef KEYCTL_WATCH_KEY
+#define KEYCTL_WATCH_KEY -1
+#endif
+#ifndef __NR_keyctl
+#define __NR_keyctl -1
+#endif
+
+#define BUF_SIZE 256
+
+static long keyctl_watch_key(int key, int watch_fd, int watch_id)
+{
+	return syscall(__NR_keyctl, KEYCTL_WATCH_KEY, key, watch_fd, watch_id);
+}
+
+static const char *key_subtypes[256] = {
+	[NOTIFY_KEY_INSTANTIATED]	= "instantiated",
+	[NOTIFY_KEY_UPDATED]		= "updated",
+	[NOTIFY_KEY_LINKED]		= "linked",
+	[NOTIFY_KEY_UNLINKED]		= "unlinked",
+	[NOTIFY_KEY_CLEARED]		= "cleared",
+	[NOTIFY_KEY_REVOKED]		= "revoked",
+	[NOTIFY_KEY_INVALIDATED]	= "invalidated",
+	[NOTIFY_KEY_SETATTR]		= "setattr",
+};
+
+static void saw_key_change(struct watch_notification *n, size_t len)
+{
+	struct key_notification *k = (struct key_notification *)n;
+
+	if (len != sizeof(struct key_notification)) {
+		fprintf(stderr, "Incorrect key message length\n");
+		return;
+	}
+
+	printf("KEY %08x change=%u[%s] aux=%u\n",
+	       k->key_id, n->subtype, key_subtypes[n->subtype], k->aux);
+}
+
+/*
+ * Consume and display events.
+ */
+static void consumer(int fd)
+{
+	unsigned char buffer[433], *p, *end;
+	union {
+		struct watch_notification n;
+		unsigned char buf1[128];
+	} n;
+	ssize_t buf_len;
+
+	for (;;) {
+		buf_len = read(fd, buffer, sizeof(buffer));
+		if (buf_len == -1) {
+			perror("read");
+			exit(1);
+		}
+
+		if (buf_len == 0) {
+			printf("-- END --\n");
+			return;
+		}
+
+		if (buf_len > sizeof(buffer)) {
+			fprintf(stderr, "Read buffer overrun: %zd\n", buf_len);
+			return;
+		}
+
+		printf("read() = %zd\n", buf_len);
+
+		p = buffer;
+		end = buffer + buf_len;
+		while (p < end) {
+			size_t largest, len;
+
+			largest = end - p;
+			if (largest > 128)
+				largest = 128;
+			if (largest < sizeof(struct watch_notification)) {
+				fprintf(stderr, "Short message header: %zu\n", largest);
+				return;
+			}
+			memcpy(&n, p, largest);
+
+			printf("NOTIFY[%03zx]: ty=%06x sy=%02x i=%08x\n",
+			       p - buffer, n.n.type, n.n.subtype, n.n.info);
+
+			len = n.n.info & WATCH_INFO_LENGTH;
+			if (len < sizeof(n.n) || len > largest) {
+				fprintf(stderr, "Bad message length: %zu/%zu\n", len, largest);
+				exit(1);
+			}
+
+			switch (n.n.type) {
+			case WATCH_TYPE_META:
+				switch (n.n.subtype) {
+				case WATCH_META_REMOVAL_NOTIFICATION:
+					printf("REMOVAL of watchpoint %08x\n",
+					       (n.n.info & WATCH_INFO_ID) >>
+					       WATCH_INFO_ID__SHIFT);
+					break;
+				case WATCH_META_LOSS_NOTIFICATION:
+					printf("-- LOSS --\n");
+					break;
+				default:
+					printf("other meta record\n");
+					break;
+				}
+				break;
+			case WATCH_TYPE_KEY_NOTIFY:
+				saw_key_change(&n.n, len);
+				break;
+			default:
+				printf("other type\n");
+				break;
+			}
+
+			p += len;
+		}
+	}
+}
+
+static struct watch_notification_filter filter = {
+	.nr_filters	= 1,
+	.filters = {
+		[0]	= {
+			.type			= WATCH_TYPE_KEY_NOTIFY,
+			.subtype_filter[0]	= UINT_MAX,
+		},
+	},
+};
+
+int main(int argc, char **argv)
+{
+	int pipefd[2], fd;
+
+	if (pipe2(pipefd, O_NOTIFICATION_PIPE) == -1) {
+		perror("pipe2");
+		exit(1);
+	}
+	fd = pipefd[0];
+
+	if (ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, BUF_SIZE) == -1) {
+		perror("watch_queue(size)");
+		exit(1);
+	}
+
+	if (ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter) == -1) {
+		perror("watch_queue(filter)");
+		exit(1);
+	}
+
+	if (keyctl_watch_key(KEY_SPEC_SESSION_KEYRING, fd, 0x01) == -1) {
+		perror("keyctl");
+		exit(1);
+	}
+
+	if (keyctl_watch_key(KEY_SPEC_USER_KEYRING, fd, 0x02) == -1) {
+		perror("keyctl");
+		exit(1);
+	}
+
+	consumer(fd);
+	exit(0);
+}

security/keys/Kconfig

···
 	 in the kernel.
 
 	 If you are unsure as to whether this is required, answer N.
+
+config KEY_NOTIFICATIONS
+	bool "Provide key/keyring change notifications"
+	depends on KEYS && WATCH_QUEUE
+	help
+	  This option provides support for getting change notifications on keys
+	  and keyrings on which the caller has View permission.  This makes use
+	  of the /dev/watch_queue misc device to handle the notification
+	  buffer and provides KEYCTL_WATCH_KEY to enable/disable watches.

security/keys/compat.c

···
 	case KEYCTL_CAPABILITIES:
 		return keyctl_capabilities(compat_ptr(arg2), arg3);
 
+	case KEYCTL_WATCH_KEY:
+		return keyctl_watch_key(arg2, arg3, arg4);
+
 	default:
 		return -EOPNOTSUPP;
 	}

security/keys/gc.c

···
 		kdebug("- %u", key->serial);
 		key_check(key);
 
+#ifdef CONFIG_KEY_NOTIFICATIONS
+		remove_watch_list(key->watchers, key->serial);
+		key->watchers = NULL;
+#endif
+
 		/* Throw away the key data if the key is instantiated */
 		if (state == KEY_IS_POSITIVE && key->type->destroy)
 			key->type->destroy(key);

security/keys/internal.h

···
 #include <linux/task_work.h>
 #include <linux/keyctl.h>
 #include <linux/refcount.h>
+#include <linux/watch_queue.h>
 #include <linux/compat.h>
 #include <linux/mm.h>
 #include <linux/vmalloc.h>
···
 			    const struct keyring_index_key *index_key,
 			    struct assoc_array_edit **_edit);
 extern int __key_link_check_live_key(struct key *keyring, struct key *key);
-extern void __key_link(struct key *key, struct assoc_array_edit **_edit);
+extern void __key_link(struct key *keyring, struct key *key,
+		       struct assoc_array_edit **_edit);
 extern void __key_link_end(struct key *keyring,
 			   const struct keyring_index_key *index_key,
 			   struct assoc_array_edit *edit);
···
 				      const struct key_match_data *match_data);
 #define KEY_LOOKUP_CREATE	0x01
 #define KEY_LOOKUP_PARTIAL	0x02
-#define KEY_LOOKUP_FOR_UNLINK	0x04
 
 extern long join_session_keyring(const char *name);
 extern void key_change_session_keyring(struct callback_head *twork);
···
 
 extern int key_task_permission(const key_ref_t key_ref,
 			       const struct cred *cred,
-			       key_perm_t perm);
+			       enum key_need_perm need_perm);
+
+static inline void notify_key(struct key *key,
+			      enum key_notification_subtype subtype, u32 aux)
+{
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	struct key_notification n = {
+		.watch.type	= WATCH_TYPE_KEY_NOTIFY,
+		.watch.subtype	= subtype,
+		.watch.info	= watch_sizeof(n),
+		.key_id		= key_serial(key),
+		.aux		= aux,
+	};
+
+	post_watch_notification(key->watchers, &n.watch, current_cred(),
+				n.key_id);
+#endif
+}
 
 /*
  * Check to see whether permission is granted to use a key in the desired way.
  */
-static inline int key_permission(const key_ref_t key_ref, unsigned perm)
+static inline int key_permission(const key_ref_t key_ref,
+				 enum key_need_perm need_perm)
 {
-	return key_task_permission(key_ref, current_cred(), perm);
+	return key_task_permission(key_ref, current_cred(), need_perm);
 }
 
 extern struct key_type key_type_request_key_auth;
···
 #endif
 
 extern long keyctl_capabilities(unsigned char __user *_buffer, size_t buflen);
+
+#ifdef CONFIG_KEY_NOTIFICATIONS
+extern long keyctl_watch_key(key_serial_t, int, int);
+#else
+static inline long keyctl_watch_key(key_serial_t key_id, int watch_fd, int watch_id)
+{
+	return -EOPNOTSUPP;
+}
+#endif
 
 /*
  * Debugging key validation

security/keys/key.c

···
 			/* mark the key as being instantiated */
 			atomic_inc(&key->user->nikeys);
 			mark_key_instantiated(key, 0);
+			notify_key(key, NOTIFY_KEY_INSTANTIATED, 0);
 
 			if (test_and_clear_bit(KEY_FLAG_USER_CONSTRUCT, &key->flags))
 				awaken = 1;
···
 				if (test_bit(KEY_FLAG_KEEP, &keyring->flags))
 					set_bit(KEY_FLAG_KEEP, &key->flags);
 
-				__key_link(key, _edit);
+				__key_link(keyring, key, _edit);
 			}
 
 			/* disable the authorisation key */
···
 		/* mark the key as being negatively instantiated */
 		atomic_inc(&key->user->nikeys);
 		mark_key_instantiated(key, -error);
+		notify_key(key, NOTIFY_KEY_INSTANTIATED, -error);
 		key->expiry = ktime_get_real_seconds() + timeout;
 		key_schedule_gc(key->expiry + key_gc_delay);
 
···
 
 		/* and link it into the destination keyring */
 		if (keyring && link_ret == 0)
-			__key_link(key, &edit);
+			__key_link(keyring, key, &edit);
 
 		/* disable the authorisation key */
 		if (authkey)
···
 	down_write(&key->sem);
 
 	ret = key->type->update(key, prep);
-	if (ret == 0)
+	if (ret == 0) {
 		/* Updating a negative key positively instantiates it */
 		mark_key_instantiated(key, 0);
+		notify_key(key, NOTIFY_KEY_UPDATED, 0);
+	}
 
 	up_write(&key->sem);
 
···
 	down_write(&key->sem);
 
 	ret = key->type->update(key, &prep);
-	if (ret == 0)
+	if (ret == 0) {
 		/* Updating a negative key positively instantiates it */
 		mark_key_instantiated(key, 0);
+		notify_key(key, NOTIFY_KEY_UPDATED, 0);
+	}
 
 	up_write(&key->sem);
 
···
 	 *   instantiated
 	 */
 	down_write_nested(&key->sem, 1);
-	if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags) &&
-	    key->type->revoke)
-		key->type->revoke(key);
+	if (!test_and_set_bit(KEY_FLAG_REVOKED, &key->flags)) {
+		notify_key(key, NOTIFY_KEY_REVOKED, 0);
+		if (key->type->revoke)
+			key->type->revoke(key);
 
-	/* set the death time to no more than the expiry time */
-	time = ktime_get_real_seconds();
-	if (key->revoked_at == 0 || key->revoked_at > time) {
-		key->revoked_at = time;
-		key_schedule_gc(key->revoked_at + key_gc_delay);
+		/* set the death time to no more than the expiry time */
+		time = ktime_get_real_seconds();
+		if (key->revoked_at == 0 || key->revoked_at > time) {
+			key->revoked_at = time;
+			key_schedule_gc(key->revoked_at + key_gc_delay);
+		}
 	}
 
 	up_write(&key->sem);
···
 
 	if (!test_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
 		down_write_nested(&key->sem, 1);
-		if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags))
+		if (!test_and_set_bit(KEY_FLAG_INVALIDATED, &key->flags)) {
+			notify_key(key, NOTIFY_KEY_INVALIDATED, 0);
 			key_schedule_gc_links();
+		}
 		up_write(&key->sem);
 	}
 }

security/keys/keyctl.c

···
 	       KEYCTL_CAPS0_MOVE
 	       ),
 	[1] = (KEYCTL_CAPS1_NS_KEYRING_NAME |
-	       KEYCTL_CAPS1_NS_KEY_TAG),
+	       KEYCTL_CAPS1_NS_KEY_TAG |
+	       (IS_ENABLED(CONFIG_KEY_NOTIFICATIONS)	? KEYCTL_CAPS1_NOTIFICATIONS : 0)
+	       ),
 };
 
 static int key_get_type_from_user(char *type,
···
 
 		/* Root is permitted to invalidate certain special keys */
 		if (capable(CAP_SYS_ADMIN)) {
-			key_ref = lookup_user_key(id, 0, 0);
+			key_ref = lookup_user_key(id, 0, KEY_SYSADMIN_OVERRIDE);
 			if (IS_ERR(key_ref))
 				goto error;
 			if (test_bit(KEY_FLAG_ROOT_CAN_INVAL,
···
 
 		/* Root is permitted to invalidate certain special keyrings */
 		if (capable(CAP_SYS_ADMIN)) {
-			keyring_ref = lookup_user_key(ringid, 0, 0);
+			keyring_ref = lookup_user_key(ringid, 0,
+						      KEY_SYSADMIN_OVERRIDE);
 			if (IS_ERR(keyring_ref))
 				goto error;
 			if (test_bit(KEY_FLAG_ROOT_CAN_CLEAR,
···
 		goto error;
 	}
 
-	key_ref = lookup_user_key(id, KEY_LOOKUP_FOR_UNLINK, 0);
+	key_ref = lookup_user_key(id, KEY_LOOKUP_PARTIAL, KEY_NEED_UNLINK);
 	if (IS_ERR(key_ref)) {
 		ret = PTR_ERR(key_ref);
 		goto error2;
···
 				key_put(instkey);
 				key_ref = lookup_user_key(keyid,
 							  KEY_LOOKUP_PARTIAL,
-							  0);
+							  KEY_AUTHTOKEN_OVERRIDE);
 				if (!IS_ERR(key_ref))
 					goto okay;
 			}
···
 	size_t key_data_len;
 
 	/* find the key first */
-	key_ref = lookup_user_key(keyid, 0, 0);
+	key_ref = lookup_user_key(keyid, 0, KEY_DEFER_PERM_CHECK);
 	if (IS_ERR(key_ref)) {
 		ret = -ENOKEY;
 		goto out;
···
 	if (group != (gid_t) -1)
 		key->gid = gid;
 
+	notify_key(key, NOTIFY_KEY_SETATTR, 0);
 	ret = 0;
 
 error_put:
···
 	/* if we're not the sysadmin, we can only change a key that we own */
 	if (capable(CAP_SYS_ADMIN) || uid_eq(key->uid, current_fsuid())) {
 		key->perm = perm;
+		notify_key(key, NOTIFY_KEY_SETATTR, 0);
 		ret = 0;
 	}
 
···
 				key_put(instkey);
 				key_ref = lookup_user_key(id,
 							  KEY_LOOKUP_PARTIAL,
-							  0);
+							  KEY_AUTHTOKEN_OVERRIDE);
 				if (!IS_ERR(key_ref))
 					goto okay;
 			}
···
 okay:
 	key = key_ref_to_ptr(key_ref);
 	ret = 0;
-	if (test_bit(KEY_FLAG_KEEP, &key->flags))
+	if (test_bit(KEY_FLAG_KEEP, &key->flags)) {
 		ret = -EPERM;
-	else
+	} else {
 		key_set_timeout(key, timeout);
+		notify_key(key, NOTIFY_KEY_SETATTR, 0);
+	}
 	key_put(key);
 
 error:
···
 			return PTR_ERR(instkey);
 		key_put(instkey);
 
-		key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL, 0);
+		key_ref = lookup_user_key(keyid, KEY_LOOKUP_PARTIAL,
+					  KEY_AUTHTOKEN_OVERRIDE);
 		if (IS_ERR(key_ref))
 			return PTR_ERR(key_ref);
 	}
···
 	return ret;
 }
 
+#ifdef CONFIG_KEY_NOTIFICATIONS
+/*
+ * Watch for changes to a key.
+ *
+ * The caller must have View permission to watch a key or keyring.
+ */
+long keyctl_watch_key(key_serial_t id, int watch_queue_fd, int watch_id)
+{
+	struct watch_queue *wqueue;
+	struct watch_list *wlist = NULL;
+	struct watch *watch = NULL;
+	struct key *key;
+	key_ref_t key_ref;
+	long ret;
+
+	if (watch_id < -1 || watch_id > 0xff)
+		return -EINVAL;
+
+	key_ref = lookup_user_key(id, KEY_LOOKUP_CREATE, KEY_NEED_VIEW);
+	if (IS_ERR(key_ref))
+		return PTR_ERR(key_ref);
+	key = key_ref_to_ptr(key_ref);
+
+	wqueue = get_watch_queue(watch_queue_fd);
+	if (IS_ERR(wqueue)) {
+		ret = PTR_ERR(wqueue);
+		goto err_key;
+	}
+
+	if (watch_id >= 0) {
+		ret = -ENOMEM;
+		if (!key->watchers) {
+			wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+			if (!wlist)
+				goto err_wqueue;
+			init_watch_list(wlist, NULL);
+		}
+
+		watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+		if (!watch)
+			goto err_wlist;
+
+		init_watch(watch, wqueue);
+		watch->id	= key->serial;
+		watch->info_id	= (u32)watch_id << WATCH_INFO_ID__SHIFT;
+
+		ret = security_watch_key(key);
+		if (ret < 0)
+			goto err_watch;
+
+		down_write(&key->sem);
+		if (!key->watchers) {
+			key->watchers = wlist;
+			wlist = NULL;
+		}
+
+		ret = add_watch_to_object(watch, key->watchers);
+		up_write(&key->sem);
+
+		if (ret == 0)
+			watch = NULL;
+	} else {
+		ret = -EBADSLT;
+		if (key->watchers) {
+			down_write(&key->sem);
+			ret = remove_watch_from_object(key->watchers,
+						       wqueue, key_serial(key),
+						       false);
+			up_write(&key->sem);
+		}
+	}
+
+err_watch:
+	kfree(watch);
+err_wlist:
+	kfree(wlist);
+err_wqueue:
+	put_watch_queue(wqueue);
+err_key:
+	key_put(key);
+	return ret;
+}
+#endif /* CONFIG_KEY_NOTIFICATIONS */
+
 /*
  * Get keyrings subsystem capabilities.
  */
···
 
 	case KEYCTL_CAPABILITIES:
 		return keyctl_capabilities((unsigned char __user *)arg2, (size_t)arg3);
+
+	case KEYCTL_WATCH_KEY:
+		return keyctl_watch_key((key_serial_t)arg2, (int)arg3, (int)arg4);
 
 	default:
 		return -EOPNOTSUPP;

security/keys/keyring.c

···
 	down_write(&keyring->sem);
 	down_write(&keyring_serialise_restrict_sem);
 
-	if (keyring->restrict_link)
+	if (keyring->restrict_link) {
 		ret = -EEXIST;
-	else if (keyring_detect_restriction_cycle(keyring, restrict_link))
+	} else if (keyring_detect_restriction_cycle(keyring, restrict_link)) {
 		ret = -EDEADLK;
-	else
+	} else {
 		keyring->restrict_link = restrict_link;
+		notify_key(keyring, NOTIFY_KEY_SETATTR, 0);
+	}
 
 	up_write(&keyring_serialise_restrict_sem);
 	up_write(&keyring->sem);
···
  * holds at most one link to any given key of a particular type+description
  * combination.
  */
-void __key_link(struct key *key, struct assoc_array_edit **_edit)
+void __key_link(struct key *keyring, struct key *key,
+		struct assoc_array_edit **_edit)
 {
 	__key_get(key);
 	assoc_array_insert_set_object(*_edit, keyring_key_to_ptr(key));
 	assoc_array_apply_edit(*_edit);
 	*_edit = NULL;
+	notify_key(keyring, NOTIFY_KEY_LINKED, key_serial(key));
 }
 
 /*
···
 	if (ret == 0)
 		ret = __key_link_check_live_key(keyring, key);
 	if (ret == 0)
-		__key_link(key, &edit);
+		__key_link(keyring, key, &edit);
 
 error_end:
 	__key_link_end(keyring, &key->index_key, edit);
···
 	struct assoc_array_edit *edit;
 
 	BUG_ON(*_edit != NULL);
-	
+
 	edit = assoc_array_delete(&keyring->keys, &keyring_assoc_array_ops,
 				  &key->index_key);
 	if (IS_ERR(edit))
···
 			 struct assoc_array_edit **_edit)
 {
 	assoc_array_apply_edit(*_edit);
+	notify_key(keyring, NOTIFY_KEY_UNLINKED, key_serial(key));
 	*_edit = NULL;
 	key_payload_reserve(keyring, keyring->datalen - KEYQUOTA_LINK_BYTES);
 }
···
 		goto error;
 
 	__key_unlink(from_keyring, key, &from_edit);
-	__key_link(key, &to_edit);
+	__key_link(to_keyring, key, &to_edit);
 error:
 	__key_link_end(to_keyring, &key->index_key, to_edit);
 	__key_unlink_end(from_keyring, key, from_edit);
···
 	} else {
 		if (edit)
 			assoc_array_apply_edit(edit);
+		notify_key(keyring, NOTIFY_KEY_CLEARED, 0);
 		key_payload_reserve(keyring, 0);
 		ret = 0;
 	}

security/keys/permission.c

···
  * key_task_permission - Check a key can be used
  * @key_ref: The key to check.
  * @cred: The credentials to use.
- * @perm: The permissions to check for.
+ * @need_perm: The permission required.
  *
  * Check to see whether permission is granted to use a key in the desired way,
  * but permit the security modules to override.
···
  * permissions bits or the LSM check.
  */
 int key_task_permission(const key_ref_t key_ref, const struct cred *cred,
-			unsigned perm)
+			enum key_need_perm need_perm)
 {
 	struct key *key;
-	key_perm_t kperm;
+	key_perm_t kperm, mask;
 	int ret;
+
+	switch (need_perm) {
+	default:
+		WARN_ON(1);
+		return -EACCES;
+	case KEY_NEED_UNLINK:
+	case KEY_SYSADMIN_OVERRIDE:
+	case KEY_AUTHTOKEN_OVERRIDE:
+	case KEY_DEFER_PERM_CHECK:
+		goto lsm;
+
+	case KEY_NEED_VIEW:	mask = KEY_OTH_VIEW;	break;
+	case KEY_NEED_READ:	mask = KEY_OTH_READ;	break;
+	case KEY_NEED_WRITE:	mask = KEY_OTH_WRITE;	break;
+	case KEY_NEED_SEARCH:	mask = KEY_OTH_SEARCH;	break;
+	case KEY_NEED_LINK:	mask = KEY_OTH_LINK;	break;
+	case KEY_NEED_SETATTR:	mask = KEY_OTH_SETATTR;	break;
+	}
 
 	key = key_ref_to_ptr(key_ref);
 
···
 	if (is_key_possessed(key_ref))
 		kperm |= key->perm >> 24;
 
-	kperm = kperm & perm & KEY_NEED_ALL;
-
-	if (kperm != perm)
+	if ((kperm & mask) != mask)
 		return -EACCES;
 
 	/* let LSM be the final arbiter */
-	return security_key_permission(key_ref, cred, perm);
+lsm:
+	return security_key_permission(key_ref, cred, need_perm);
 }
 EXPORT_SYMBOL(key_task_permission);
 

security/keys/process_keys.c

···
  * returned key reference.
  */
 key_ref_t lookup_user_key(key_serial_t id, unsigned long lflags,
-			  key_perm_t perm)
+			  enum key_need_perm need_perm)
 {
 	struct keyring_search_context ctx = {
 		.match_data.cmp		= lookup_user_key_possessed,
···
 
 	/* unlink does not use the nominated key in any way, so can skip all
 	 * the permission checks as it is only concerned with the keyring */
-	if (lflags & KEY_LOOKUP_FOR_UNLINK) {
-		ret = 0;
-		goto error;
-	}
-
-	if (!(lflags & KEY_LOOKUP_PARTIAL)) {
-		ret = wait_for_key_construction(key, true);
-		switch (ret) {
-		case -ERESTARTSYS:
-			goto invalid_key;
-		default:
-			if (perm)
+	if (need_perm != KEY_NEED_UNLINK) {
+		if (!(lflags & KEY_LOOKUP_PARTIAL)) {
+			ret = wait_for_key_construction(key, true);
+			switch (ret) {
+			case -ERESTARTSYS:
 				goto invalid_key;
-		case 0:
-			break;
+			default:
+				if (need_perm != KEY_AUTHTOKEN_OVERRIDE &&
+				    need_perm != KEY_DEFER_PERM_CHECK)
+					goto invalid_key;
+			case 0:
+				break;
+			}
+		} else if (need_perm != KEY_DEFER_PERM_CHECK) {
+			ret = key_validate(key);
+			if (ret < 0)
+				goto invalid_key;
 		}
-	} else if (perm) {
-		ret = key_validate(key);
-		if (ret < 0)
+
+		ret = -EIO;
+		if (!(lflags & KEY_LOOKUP_PARTIAL) &&
+		    key_read_state(key) == KEY_IS_UNINSTANTIATED)
 			goto invalid_key;
 	}
-
-	ret = -EIO;
-	if (!(lflags & KEY_LOOKUP_PARTIAL) &&
-	    key_read_state(key) == KEY_IS_UNINSTANTIATED)
-		goto invalid_key;
 
 	/* check the permissions */
-	ret = key_task_permission(key_ref, ctx.cred, perm);
+	ret = key_task_permission(key_ref, ctx.cred, need_perm);
 	if (ret < 0)
 		goto invalid_key;
 

security/keys/request_key.c

···
 		goto key_already_present;
 
 	if (dest_keyring)
-		__key_link(key, &edit);
+		__key_link(dest_keyring, key, &edit);
 
 	mutex_unlock(&key_construction_mutex);
 	if (dest_keyring)
···
 	if (dest_keyring) {
 		ret = __key_link_check_live_key(dest_keyring, key);
 		if (ret == 0)
-			__key_link(key, &edit);
+			__key_link(dest_keyring, key, &edit);
 		__key_link_end(dest_keyring, &ctx->index_key, edit);
 		if (ret < 0)
 			goto link_check_failed;

security/security.c

···
 }
 EXPORT_SYMBOL(security_inode_getsecctx);
 
+#ifdef CONFIG_WATCH_QUEUE
+int security_post_notification(const struct cred *w_cred,
+			       const struct cred *cred,
+			       struct watch_notification *n)
+{
+	return call_int_hook(post_notification, 0, w_cred, cred, n);
+}
+#endif /* CONFIG_WATCH_QUEUE */
+
+#ifdef CONFIG_KEY_NOTIFICATIONS
+int security_watch_key(struct key *key)
+{
+	return call_int_hook(watch_key, 0, key);
+}
+#endif
+
 #ifdef CONFIG_SECURITY_NETWORK
 
 int security_unix_stream_connect(struct sock *sock, struct sock *other, struct sock *newsk)
···
 	call_void_hook(key_free, key);
 }
 
-int security_key_permission(key_ref_t key_ref,
-			    const struct cred *cred, unsigned perm)
+int security_key_permission(key_ref_t key_ref, const struct cred *cred,
+			    enum key_need_perm need_perm)
 {
-	return call_int_hook(key_permission, 0, key_ref, cred, perm);
+	return call_int_hook(key_permission, 0, key_ref, cred, need_perm);
 }
 
 int security_key_getsecurity(struct key *key, char **_buffer)

security/selinux/hooks.c

···
 
 static int selinux_key_permission(key_ref_t key_ref,
 				  const struct cred *cred,
-				  unsigned perm)
+				  enum key_need_perm need_perm)
 {
 	struct key *key;
 	struct key_security_struct *ksec;
-	u32 sid;
+	u32 perm, sid;
 
-	/* if no specific permissions are requested, we skip the
-	   permission check. No serious, additional covert channels
-	   appear to be created. */
-	if (perm == 0)
+	switch (need_perm) {
+	case KEY_NEED_VIEW:
+		perm = KEY__VIEW;
+		break;
+	case KEY_NEED_READ:
+		perm = KEY__READ;
+		break;
+	case KEY_NEED_WRITE:
+		perm = KEY__WRITE;
+		break;
+	case KEY_NEED_SEARCH:
+		perm = KEY__SEARCH;
+		break;
+	case KEY_NEED_LINK:
+		perm = KEY__LINK;
+		break;
+	case KEY_NEED_SETATTR:
+		perm = KEY__SETATTR;
+		break;
+	case KEY_NEED_UNLINK:
+	case KEY_SYSADMIN_OVERRIDE:
+	case KEY_AUTHTOKEN_OVERRIDE:
+	case KEY_DEFER_PERM_CHECK:
 		return 0;
+	default:
+		WARN_ON(1);
+		return -EPERM;
+
+	}
 
 	sid = cred_sid(cred);
-
 	key = key_ref_to_ptr(key_ref);
 	ksec = key->security;
 
···
 	*_buffer = context;
 	return rc;
 }
+
+#ifdef CONFIG_KEY_NOTIFICATIONS
+static int selinux_watch_key(struct key *key)
+{
+	struct key_security_struct *ksec = key->security;
+	u32 sid = current_sid();
+
+	return avc_has_perm(&selinux_state,
+			    sid, ksec->sid, SECCLASS_KEY, KEY__VIEW, NULL);
+}
+#endif
 #endif
 
 #ifdef CONFIG_SECURITY_INFINIBAND
···
 	LSM_HOOK_INIT(key_free, selinux_key_free),
 	LSM_HOOK_INIT(key_permission, selinux_key_permission),
 	LSM_HOOK_INIT(key_getsecurity, selinux_key_getsecurity),
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	LSM_HOOK_INIT(watch_key, selinux_watch_key),
+#endif
 #endif
 
 #ifdef CONFIG_AUDIT

security/smack/smack_lsm.c

···
 #include <linux/parser.h>
 #include <linux/fs_context.h>
 #include <linux/fs_parser.h>
+#include <linux/watch_queue.h>
 #include "smack.h"
 
 #define TRANS_TRUE	"TRUE"
···
  * smack_key_permission - Smack access on a key
  * @key_ref: gets to the object
  * @cred: the credentials to use
- * @perm: requested key permissions
+ * @need_perm: requested key permission
  *
  * Return 0 if the task has read and write to the object,
  * an error code otherwise
  */
 static int smack_key_permission(key_ref_t key_ref,
-				const struct cred *cred, unsigned perm)
+				const struct cred *cred,
+				enum key_need_perm need_perm)
 {
 	struct key *keyp;
 	struct smk_audit_info ad;
···
 	/*
 	 * Validate requested permissions
 	 */
-	if (perm & ~KEY_NEED_ALL)
+	switch (need_perm) {
+	case KEY_NEED_READ:
+	case KEY_NEED_SEARCH:
+	case KEY_NEED_VIEW:
+		request |= MAY_READ;
+		break;
+	case KEY_NEED_WRITE:
+	case KEY_NEED_LINK:
+	case KEY_NEED_SETATTR:
+		request |= MAY_WRITE;
+		break;
+	case KEY_NEED_UNSPECIFIED:
+	case KEY_NEED_UNLINK:
+	case KEY_SYSADMIN_OVERRIDE:
+	case KEY_AUTHTOKEN_OVERRIDE:
+	case KEY_DEFER_PERM_CHECK:
+		return 0;
+	default:
 		return -EINVAL;
+	}
 
 	keyp = key_ref_to_ptr(key_ref);
 	if (keyp == NULL)
···
 	if (tkp == NULL)
 		return -EACCES;
 
-	if (smack_privileged_cred(CAP_MAC_OVERRIDE, cred))
+	if (smack_privileged(CAP_MAC_OVERRIDE))
 		return 0;
 
 #ifdef CONFIG_AUDIT
···
 	ad.a.u.key_struct.key = keyp->serial;
 	ad.a.u.key_struct.key_desc = keyp->description;
 #endif
-	if (perm & (KEY_NEED_READ | KEY_NEED_SEARCH | KEY_NEED_VIEW))
-		request |= MAY_READ;
-	if (perm & (KEY_NEED_WRITE | KEY_NEED_LINK | KEY_NEED_SETATTR))
-		request |= MAY_WRITE;
 	rc = smk_access(tkp, keyp->security, request, &ad);
 	rc = smk_bu_note("key access", tkp, keyp->security, request, rc);
 	return rc;
···
 	return length;
 }
 
+
+#ifdef CONFIG_KEY_NOTIFICATIONS
+/**
+ * smack_watch_key - Smack access to watch a key for notifications.
+ * @key: The key to be watched
+ *
+ * Return 0 if the @watch->cred has permission to read from the key object and
+ * an error otherwise.
+ */
+static int smack_watch_key(struct key *key)
+{
+	struct smk_audit_info ad;
+	struct smack_known *tkp = smk_of_current();
+	int rc;
+
+	if (key == NULL)
+		return -EINVAL;
+	/*
+	 * If the key hasn't been initialized give it access so that
+	 * it may do so.
+	 */
+	if (key->security == NULL)
+		return 0;
+	/*
+	 * This should not occur
+	 */
+	if (tkp == NULL)
+		return -EACCES;
+
+	if (smack_privileged_cred(CAP_MAC_OVERRIDE, current_cred()))
+		return 0;
+
+#ifdef CONFIG_AUDIT
+	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_KEY);
+	ad.a.u.key_struct.key = key->serial;
+	ad.a.u.key_struct.key_desc = key->description;
+#endif
+	rc = smk_access(tkp, key->security, MAY_READ, &ad);
+	rc = smk_bu_note("key watch", tkp, key->security, MAY_READ, rc);
+	return rc;
+}
+#endif /* CONFIG_KEY_NOTIFICATIONS */
 #endif /* CONFIG_KEYS */
+
+#ifdef CONFIG_WATCH_QUEUE
+/**
+ * smack_post_notification - Smack access to post a notification to a queue
+ * @w_cred: The credentials of the watcher.
+ * @cred: The credentials of the event source (may be NULL).
+ * @n: The notification message to be posted.
+ */
+static int smack_post_notification(const struct cred *w_cred,
+				   const struct cred *cred,
+				   struct watch_notification *n)
+{
+	struct smk_audit_info ad;
+	struct smack_known *subj, *obj;
+	int rc;
+
+	/* Always let maintenance notifications through. */
+	if (n->type == WATCH_TYPE_META)
+		return 0;
+
+	if (!cred)
+		return 0;
+	subj = smk_of_task(smack_cred(cred));
+	obj = smk_of_task(smack_cred(w_cred));
+
+	smk_ad_init(&ad, __func__, LSM_AUDIT_DATA_NOTIFICATION);
+	rc = smk_access(subj, obj, MAY_WRITE, &ad);
+	rc = smk_bu_note("notification", subj, obj, MAY_WRITE, rc);
+	return rc;
+}
+#endif /* CONFIG_WATCH_QUEUE */
 
 /*
  * Smack Audit hooks
···
 	LSM_HOOK_INIT(key_free, smack_key_free),
 	LSM_HOOK_INIT(key_permission, smack_key_permission),
 	LSM_HOOK_INIT(key_getsecurity, smack_key_getsecurity),
+#ifdef CONFIG_KEY_NOTIFICATIONS
+	LSM_HOOK_INIT(watch_key, smack_watch_key),
+#endif
 #endif /* CONFIG_KEYS */
+
+#ifdef CONFIG_WATCH_QUEUE
+	LSM_HOOK_INIT(post_notification, smack_post_notification),
+#endif
 
  /* Audit hooks */
 #ifdef CONFIG_AUDIT