[PATCH] Keys: Add possessor permissions to keys [try #3]

The attached patch adds extra permission grants to keys for the possessor of a
key in addition to the owner, group and other permissions bits. This makes
SUID binaries easier to support without going as far as labelling keys and key
targets using the LSM facilities.

This patch adds a second "pointer type" to key structures (struct key_ref *)
that can have the bottom bit of the address set to indicate the possession of
a key. This is propagated through searches from the keyring to the discovered
key. It has been made a separate type so that the compiler can spot attempts
to dereference a potentially incorrect pointer.

The "possession" attribute can't be attached to a key structure directly as
it's not an intrinsic property of a key.

Pointers to keys have been replaced with struct key_ref *'s wherever
possession information needs to be passed through.

This does assume that the bottom bit of the pointer will always be zero on
return from kmem_cache_alloc().

The key reference type has been made into a typedef so that at least it can be
located in the sources, even though it's basically a pointer to an undefined
type. I've also renamed the accessor functions to be more useful, and all
reference variables should now end in "_ref".

Signed-Off-By: David Howells <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/keys.txt

···
 ======================
 
 Keys have an owner user ID, a group access ID, and a permissions mask. The mask
-has up to eight bits each for user, group and other access. Only five of each
-set of eight bits are defined. These permissions granted are:
+has up to eight bits each for possessor, user, group and other access. Only
+five of each set of eight bits are defined. These permissions granted are:
 
  (*) View
 
···
      type, description and permissions. The payload of the key is not available
      this way:
 
-	SERIAL   FLAGS  USAGE EXPY PERM   UID   GID   TYPE      DESCRIPTION: SUMMARY
-	00000001 I-----    39 perm 1f0000     0     0 keyring   _uid_ses.0: 1/4
-	00000002 I-----     2 perm 1f0000     0     0 keyring   _uid.0: empty
-	00000007 I-----     1 perm 1f0000     0     0 keyring   _pid.1: empty
-	0000018d I-----     1 perm 1f0000     0     0 keyring   _pid.412: empty
-	000004d2 I--Q--     1 perm 1f0000    32    -1 keyring   _uid.32: 1/4
-	000004d3 I--Q--     3 perm 1f0000    32    -1 keyring   _uid_ses.32: empty
-	00000892 I--QU-     1 perm 1f0000     0     0 user      metal:copper: 0
-	00000893 I--Q-N     1  35s 1f0000     0     0 user      metal:silver: 0
-	00000894 I--Q--     1  10h 1f0000     0     0 user      metal:gold: 0
+	SERIAL   FLAGS  USAGE EXPY PERM     UID   GID   TYPE      DESCRIPTION: SUMMARY
+	00000001 I-----    39 perm 1f1f0000     0     0 keyring   _uid_ses.0: 1/4
+	00000002 I-----     2 perm 1f1f0000     0     0 keyring   _uid.0: empty
+	00000007 I-----     1 perm 1f1f0000     0     0 keyring   _pid.1: empty
+	0000018d I-----     1 perm 1f1f0000     0     0 keyring   _pid.412: empty
+	000004d2 I--Q--     1 perm 1f1f0000    32    -1 keyring   _uid.32: 1/4
+	000004d3 I--Q--     3 perm 1f1f0000    32    -1 keyring   _uid_ses.32: empty
+	00000892 I--QU-     1 perm 1f000000     0     0 user      metal:copper: 0
+	00000893 I--Q-N     1  35s 1f1f0000     0     0 user      metal:silver: 0
+	00000894 I--Q--     1  10h 001f0000     0     0 user      metal:gold: 0
 
      The flags are:
 
···
 two different users opening the same file is left to the filesystem author to
 solve.
 
+Note that there are two different types of pointers to keys that may be
+encountered:
+
+ (*) struct key *
+
+     This simply points to the key structure itself. Key structures will be at
+     least four-byte aligned.
+
+ (*) key_ref_t
+
+     This is equivalent to a struct key *, but the least significant bit is set
+     if the caller "possesses" the key. By "possession" it is meant that the
+     calling processes has a searchable link to the key from one of its
+     keyrings. There are three functions for dealing with these:
+
+	key_ref_t make_key_ref(const struct key *key,
+			       unsigned long possession);
+
+	struct key *key_ref_to_ptr(const key_ref_t key_ref);
+
+	unsigned long is_key_possessed(const key_ref_t key_ref);
+
+     The first function constructs a key reference from a key pointer and
+     possession information (which must be 0 or 1 and not any other value).
+
+     The second function retrieves the key pointer from a reference and the
+     third retrieves the possession flag.
+
 When accessing a key's payload contents, certain precautions must be taken to
 prevent access vs modification races. See the section "Notes on accessing
 payload contents" for more information.
···
 
 	void key_put(struct key *key);
 
-    This can be called from interrupt context. If CONFIG_KEYS is not set then
+    Or:
+
+	void key_ref_put(key_ref_t key_ref);
+
+    These can be called from interrupt context. If CONFIG_KEYS is not set then
     the argument will not be parsed.
 
 
···
 
 (*) If a keyring was found in the search, this can be further searched by:
 
-	struct key *keyring_search(struct key *keyring,
-				   const struct key_type *type,
-				   const char *description)
+	key_ref_t keyring_search(key_ref_t keyring_ref,
+				 const struct key_type *type,
+				 const char *description)
 
     This searches the keyring tree specified for a matching key. Error ENOKEY
-    is returned upon failure. If successful, the returned key will need to be
-    released.
+    is returned upon failure (use IS_ERR/PTR_ERR to determine). If successful,
+    the returned key will need to be released.
+
+    The possession attribute from the keyring reference is used to control
+    access through the permissions mask and is propagated to the returned key
+    reference pointer if successful.
 
 
 (*) To check the validity of a key, this function can be called:
···
 key->payload.data. One of the following ways must be selected to access the
 data:
 
- (1) Unmodifyable key type.
+ (1) Unmodifiable key type.
 
      If the key type does not have a modify method, then the key's payload can
      be accessed without any form of locking, provided that it's known to be

include/linux/key-ui.h

···
 /*
  * check to see whether permission is granted to use a key in the desired way
  */
-static inline int key_permission(const struct key *key, key_perm_t perm)
+static inline int key_permission(const key_ref_t key_ref, key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == current->fsuid)
+	if (is_key_possessed(key_ref))
+		kperm = key->perm >> 24;
+	else if (key->uid == current->fsuid)
 		kperm = key->perm >> 16;
 	else if (key->gid != -1 &&
 		 key->perm & KEY_GRP_ALL &&
···
  * check to see whether permission is granted to use a key in at least one of
  * the desired ways
  */
-static inline int key_any_permission(const struct key *key, key_perm_t perm)
+static inline int key_any_permission(const key_ref_t key_ref, key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == current->fsuid)
+	if (is_key_possessed(key_ref))
+		kperm = key->perm >> 24;
+	else if (key->uid == current->fsuid)
 		kperm = key->perm >> 16;
 	else if (key->gid != -1 &&
 		 key->perm & KEY_GRP_ALL &&
···
 	return ret;
 }
 
-static inline int key_task_permission(const struct key *key,
+static inline int key_task_permission(const key_ref_t key_ref,
 				      struct task_struct *context,
 				      key_perm_t perm)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	key_perm_t kperm;
 
-	if (key->uid == context->fsuid) {
+	if (is_key_possessed(key_ref)) {
+		kperm = key->perm >> 24;
+	}
+	else if (key->uid == context->fsuid) {
 		kperm = key->perm >> 16;
 	}
 	else if (key->gid != -1 &&
···
 
 }
 
-extern struct key *lookup_user_key(struct task_struct *context,
-				   key_serial_t id, int create, int partial,
-				   key_perm_t perm);
+extern key_ref_t lookup_user_key(struct task_struct *context,
+				 key_serial_t id, int create, int partial,
+				 key_perm_t perm);
 
 extern long join_session_keyring(const char *name);
 

include/linux/key.h

···
 
 #undef KEY_DEBUGGING
 
-#define KEY_USR_VIEW	0x00010000	/* user can view a key's attributes */
-#define KEY_USR_READ	0x00020000	/* user can read key payload / view keyring */
-#define KEY_USR_WRITE	0x00040000	/* user can update key payload / add link to keyring */
-#define KEY_USR_SEARCH	0x00080000	/* user can find a key in search / search a keyring */
-#define KEY_USR_LINK	0x00100000	/* user can create a link to a key/keyring */
+#define KEY_POS_VIEW	0x01000000	/* possessor can view a key's attributes */
+#define KEY_POS_READ	0x02000000	/* possessor can read key payload / view keyring */
+#define KEY_POS_WRITE	0x04000000	/* possessor can update key payload / add link to keyring */
+#define KEY_POS_SEARCH	0x08000000	/* possessor can find a key in search / search a keyring */
+#define KEY_POS_LINK	0x10000000	/* possessor can create a link to a key/keyring */
+#define KEY_POS_ALL	0x1f000000
+
+#define KEY_USR_VIEW	0x00010000	/* user permissions... */
+#define KEY_USR_READ	0x00020000
+#define KEY_USR_WRITE	0x00040000
+#define KEY_USR_SEARCH	0x00080000
+#define KEY_USR_LINK	0x00100000
 #define KEY_USR_ALL	0x001f0000
 
 #define KEY_GRP_VIEW	0x00000100	/* group permissions... */
···
 struct key_owner;
 struct keyring_list;
 struct keyring_name;
+
+/*****************************************************************************/
+/*
+ * key reference with possession attribute handling
+ *
+ * NOTE! key_ref_t is a typedef'd pointer to a type that is not actually
+ * defined. This is because we abuse the bottom bit of the reference to carry a
+ * flag to indicate whether the calling process possesses that key in one of
+ * its keyrings.
+ *
+ * the key_ref_t has been made a separate type so that the compiler can reject
+ * attempts to dereference it without proper conversion.
+ *
+ * the three functions are used to assemble and disassemble references
+ */
+typedef struct __key_reference_with_attributes *key_ref_t;
+
+static inline key_ref_t make_key_ref(const struct key *key,
+				     unsigned long possession)
+{
+	return (key_ref_t) ((unsigned long) key | possession);
+}
+
+static inline struct key *key_ref_to_ptr(const key_ref_t key_ref)
+{
+	return (struct key *) ((unsigned long) key_ref & ~1UL);
+}
+
+static inline unsigned long is_key_possessed(const key_ref_t key_ref)
+{
+	return (unsigned long) key_ref & 1UL;
+}
 
 /*****************************************************************************/
 /*
···
 	return key;
 }
 
+static inline void key_ref_put(key_ref_t key_ref)
+{
+	key_put(key_ref_to_ptr(key_ref));
+}
+
 extern struct key *request_key(struct key_type *type,
 			       const char *description,
 			       const char *callout_info);
 
 extern int key_validate(struct key *key);
 
-extern struct key *key_create_or_update(struct key *keyring,
-					const char *type,
-					const char *description,
-					const void *payload,
-					size_t plen,
-					int not_in_quota);
+extern key_ref_t key_create_or_update(key_ref_t keyring,
+				      const char *type,
+				      const char *description,
+				      const void *payload,
+				      size_t plen,
+				      int not_in_quota);
 
-extern int key_update(struct key *key,
+extern int key_update(key_ref_t key,
 		      const void *payload,
 		      size_t plen);
 
···
 
 extern int keyring_clear(struct key *keyring);
 
-extern struct key *keyring_search(struct key *keyring,
-				  struct key_type *type,
-				  const char *description);
+extern key_ref_t keyring_search(key_ref_t keyring,
+				struct key_type *type,
+				const char *description);
 
 extern int keyring_add_key(struct key *keyring,
 			   struct key *key);
···
 #define key_serial(k)			0
 #define key_get(k) 			({ NULL; })
 #define key_put(k)			do { } while(0)
+#define key_ref_put(k)			do { } while(0)
+#define make_key_ref(k)			({ NULL; })
+#define key_ref_to_ptr(k)		({ NULL; })
+#define is_key_possessed(k)		0
 #define alloc_uid_keyring(u)		0
 #define switch_uid_keyring(u)		do { } while(0)
 #define __install_session_keyring(t, k)	({ NULL; })

security/keys/internal.h

···
 
 extern int __key_link(struct key *keyring, struct key *key);
 
-extern struct key *__keyring_search_one(struct key *keyring,
-					const struct key_type *type,
-					const char *description,
-					key_perm_t perm);
+extern key_ref_t __keyring_search_one(key_ref_t keyring_ref,
+				      const struct key_type *type,
+				      const char *description,
+				      key_perm_t perm);
 
 extern struct key *keyring_search_instkey(struct key *keyring,
 					  key_serial_t target_id);
 
 typedef int (*key_match_func_t)(const struct key *, const void *);
 
-extern struct key *keyring_search_aux(struct key *keyring,
-				      struct task_struct *tsk,
-				      struct key_type *type,
-				      const void *description,
-				      key_match_func_t match);
+extern key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+				    struct task_struct *tsk,
+				    struct key_type *type,
+				    const void *description,
+				    key_match_func_t match);
 
-extern struct key *search_process_keyrings(struct key_type *type,
-					   const void *description,
-					   key_match_func_t match,
-					   struct task_struct *tsk);
+extern key_ref_t search_process_keyrings(struct key_type *type,
+					 const void *description,
+					 key_match_func_t match,
+					 struct task_struct *tsk);
 
 extern struct key *find_keyring_by_name(const char *name, key_serial_t bound);
 

security/keys/key.c

···
  * - the key has an incremented refcount
  * - we need to put the key if we get an error
  */
-static inline struct key *__key_update(struct key *key, const void *payload,
-				       size_t plen)
+static inline key_ref_t __key_update(key_ref_t key_ref,
+				     const void *payload, size_t plen)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	int ret;
 
 	/* need write permission on the key to update it */
 	ret = -EACCES;
-	if (!key_permission(key, KEY_WRITE))
+	if (!key_permission(key_ref, KEY_WRITE))
 		goto error;
 
 	ret = -EEXIST;
···
 
 	if (ret < 0)
 		goto error;
- out:
-	return key;
+out:
+	return key_ref;
 
- error:
+error:
 	key_put(key);
-	key = ERR_PTR(ret);
+	key_ref = ERR_PTR(ret);
 	goto out;
 
 } /* end __key_update() */
···
  * search the specified keyring for a key of the same description; if one is
  * found, update it, otherwise add a new one
  */
-struct key *key_create_or_update(struct key *keyring,
-				 const char *type,
-				 const char *description,
-				 const void *payload,
-				 size_t plen,
-				 int not_in_quota)
+key_ref_t key_create_or_update(key_ref_t keyring_ref,
+			       const char *type,
+			       const char *description,
+			       const void *payload,
+			       size_t plen,
+			       int not_in_quota)
 {
 	struct key_type *ktype;
-	struct key *key = NULL;
+	struct key *keyring, *key = NULL;
 	key_perm_t perm;
+	key_ref_t key_ref;
 	int ret;
-
-	key_check(keyring);
 
 	/* look up the key type to see if it's one of the registered kernel
 	 * types */
 	ktype = key_type_lookup(type);
 	if (IS_ERR(ktype)) {
-		key = ERR_PTR(-ENODEV);
+		key_ref = ERR_PTR(-ENODEV);
 		goto error;
 	}
 
-	ret = -EINVAL;
+	key_ref = ERR_PTR(-EINVAL);
 	if (!ktype->match || !ktype->instantiate)
 		goto error_2;
+
+	keyring = key_ref_to_ptr(keyring_ref);
+
+	key_check(keyring);
+
+	down_write(&keyring->sem);
+
+	/* if we're going to allocate a new key, we're going to have
+	 * to modify the keyring */
+	key_ref = ERR_PTR(-EACCES);
+	if (!key_permission(keyring_ref, KEY_WRITE))
+		goto error_3;
 
 	/* search for an existing key of the same type and description in the
 	 * destination keyring
 	 */
-	down_write(&keyring->sem);
-
-	key = __keyring_search_one(keyring, ktype, description, 0);
-	if (!IS_ERR(key))
+	key_ref = __keyring_search_one(keyring_ref, ktype, description, 0);
+	if (!IS_ERR(key_ref))
 		goto found_matching_key;
 
-	/* if we're going to allocate a new key, we're going to have to modify
-	 * the keyring */
-	ret = -EACCES;
-	if (!key_permission(keyring, KEY_WRITE))
-		goto error_3;
-
 	/* decide on the permissions we want */
-	perm = KEY_USR_VIEW | KEY_USR_SEARCH | KEY_USR_LINK;
+	perm = KEY_POS_VIEW | KEY_POS_SEARCH | KEY_POS_LINK;
+	perm |= KEY_USR_VIEW | KEY_USR_SEARCH | KEY_USR_LINK;
 
 	if (ktype->read)
-		perm |= KEY_USR_READ;
+		perm |= KEY_POS_READ | KEY_USR_READ;
 
 	if (ktype == &key_type_keyring || ktype->update)
 		perm |= KEY_USR_WRITE;
···
 	key = key_alloc(ktype, description, current->fsuid, current->fsgid,
 			perm, not_in_quota);
 	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+		key_ref = ERR_PTR(PTR_ERR(key));
 		goto error_3;
 	}
 
···
 	ret = __key_instantiate_and_link(key, payload, plen, keyring, NULL);
 	if (ret < 0) {
 		key_put(key);
-		key = ERR_PTR(ret);
+		key_ref = ERR_PTR(ret);
+		goto error_3;
 	}
+
+	key_ref = make_key_ref(key, is_key_possessed(keyring_ref));
 
  error_3:
 	up_write(&keyring->sem);
  error_2:
 	key_type_put(ktype);
  error:
-	return key;
+	return key_ref;
 
  found_matching_key:
 	/* we found a matching key, so we're going to try to update it
···
 	up_write(&keyring->sem);
 	key_type_put(ktype);
 
-	key = __key_update(key, payload, plen);
+	key_ref = __key_update(key_ref, payload, plen);
 	goto error;
 
 } /* end key_create_or_update() */
···
 /*
  * update a key
  */
-int key_update(struct key *key, const void *payload, size_t plen)
+int key_update(key_ref_t key_ref, const void *payload, size_t plen)
 {
+	struct key *key = key_ref_to_ptr(key_ref);
 	int ret;
 
 	key_check(key);
 
 	/* the key must be writable */
 	ret = -EACCES;
-	if (!key_permission(key, KEY_WRITE))
+	if (!key_permission(key_ref, KEY_WRITE))
 		goto error;
 
 	/* attempt to update it if supported */

security/keys/keyctl.c

···
 			    size_t plen,
 			    key_serial_t ringid)
 {
-	struct key *keyring, *key;
+	key_ref_t keyring_ref, key_ref;
 	char type[32], *description;
 	void *payload;
 	long dlen, ret;
···
 	}
 
 	/* find the target keyring (which must be writable) */
-	keyring = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
-	if (IS_ERR(keyring)) {
-		ret = PTR_ERR(keyring);
+	keyring_ref = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
+	if (IS_ERR(keyring_ref)) {
+		ret = PTR_ERR(keyring_ref);
 		goto error3;
 	}
 
 	/* create or update the requested key and add it to the target
 	 * keyring */
-	key = key_create_or_update(keyring, type, description,
-				   payload, plen, 0);
-	if (!IS_ERR(key)) {
-		ret = key->serial;
-		key_put(key);
+	key_ref = key_create_or_update(keyring_ref, type, description,
+				       payload, plen, 0);
+	if (!IS_ERR(key_ref)) {
+		ret = key_ref_to_ptr(key_ref)->serial;
+		key_ref_put(key_ref);
 	}
 	else {
-		ret = PTR_ERR(key);
+		ret = PTR_ERR(key_ref);
 	}
 
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error3:
 	kfree(payload);
  error2:
···
 				key_serial_t destringid)
 {
 	struct key_type *ktype;
-	struct key *key, *dest;
+	struct key *key;
+	key_ref_t dest_ref;
 	char type[32], *description, *callout_info;
 	long dlen, ret;
 
···
 	}
 
 	/* get the destination keyring if specified */
-	dest = NULL;
+	dest_ref = NULL;
 	if (destringid) {
-		dest = lookup_user_key(NULL, destringid, 1, 0, KEY_WRITE);
-		if (IS_ERR(dest)) {
-			ret = PTR_ERR(dest);
+		dest_ref = lookup_user_key(NULL, destringid, 1, 0, KEY_WRITE);
+		if (IS_ERR(dest_ref)) {
+			ret = PTR_ERR(dest_ref);
 			goto error3;
 		}
 	}
···
 	}
 
 	/* do the search */
-	key = request_key_and_link(ktype, description, callout_info, dest);
+	key = request_key_and_link(ktype, description, callout_info,
+				   key_ref_to_ptr(dest_ref));
 	if (IS_ERR(key)) {
 		ret = PTR_ERR(key);
 		goto error5;
···
  error5:
 	key_type_put(ktype);
  error4:
-	key_put(dest);
+	key_ref_put(dest_ref);
  error3:
 	kfree(callout_info);
  error2:
···
  */
 long keyctl_get_keyring_ID(key_serial_t id, int create)
 {
-	struct key *key;
+	key_ref_t key_ref;
 	long ret;
 
-	key = lookup_user_key(NULL, id, create, 0, KEY_SEARCH);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, create, 0, KEY_SEARCH);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error;
 	}
 
-	ret = key->serial;
-	key_put(key);
+	ret = key_ref_to_ptr(key_ref)->serial;
+	key_ref_put(key_ref);
  error:
 	return ret;
 
···
 		       const void __user *_payload,
 		       size_t plen)
 {
-	struct key *key;
+	key_ref_t key_ref;
 	void *payload;
 	long ret;
 
···
 	}
 
 	/* find the target key (which must be writable) */
-	key = lookup_user_key(NULL, id, 0, 0, KEY_WRITE);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 0, 0, KEY_WRITE);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error2;
 	}
 
 	/* update the key */
-	ret = key_update(key, payload, plen);
+	ret = key_update(key_ref, payload, plen);
 
-	key_put(key);
+	key_ref_put(key_ref);
  error2:
 	kfree(payload);
  error:
···
  */
 long keyctl_revoke_key(key_serial_t id)
 {
-	struct key *key;
+	key_ref_t key_ref;
 	long ret;
 
-	key = lookup_user_key(NULL, id, 0, 0, KEY_WRITE);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 0, 0, KEY_WRITE);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error;
 	}
 
-	key_revoke(key);
+	key_revoke(key_ref_to_ptr(key_ref));
 	ret = 0;
 
-	key_put(key);
+	key_ref_put(key_ref);
  error:
 	return ret;
 
···
  */
 long keyctl_keyring_clear(key_serial_t ringid)
 {
-	struct key *keyring;
+	key_ref_t keyring_ref;
 	long ret;
 
-	keyring = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
-	if (IS_ERR(keyring)) {
-		ret = PTR_ERR(keyring);
+	keyring_ref = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
+	if (IS_ERR(keyring_ref)) {
+		ret = PTR_ERR(keyring_ref);
 		goto error;
 	}
 
-	ret = keyring_clear(keyring);
+	ret = keyring_clear(key_ref_to_ptr(keyring_ref));
 
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error:
 	return ret;
 
···
  */
 long keyctl_keyring_link(key_serial_t id, key_serial_t ringid)
 {
-	struct key *keyring, *key;
+	key_ref_t keyring_ref, key_ref;
 	long ret;
 
-	keyring = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
-	if (IS_ERR(keyring)) {
-		ret = PTR_ERR(keyring);
+	keyring_ref = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
+	if (IS_ERR(keyring_ref)) {
+		ret = PTR_ERR(keyring_ref);
 		goto error;
 	}
 
-	key = lookup_user_key(NULL, id, 1, 0, KEY_LINK);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 1, 0, KEY_LINK);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error2;
 	}
 
-	ret = key_link(keyring, key);
+	ret = key_link(key_ref_to_ptr(keyring_ref), key_ref_to_ptr(key_ref));
 
-	key_put(key);
+	key_ref_put(key_ref);
  error2:
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error:
 	return ret;
 
···
  */
 long keyctl_keyring_unlink(key_serial_t id, key_serial_t ringid)
 {
-	struct key *keyring, *key;
+	key_ref_t keyring_ref, key_ref;
 	long ret;
 
-	keyring = lookup_user_key(NULL, ringid, 0, 0, KEY_WRITE);
-	if (IS_ERR(keyring)) {
-		ret = PTR_ERR(keyring);
+	keyring_ref = lookup_user_key(NULL, ringid, 0, 0, KEY_WRITE);
+	if (IS_ERR(keyring_ref)) {
+		ret = PTR_ERR(keyring_ref);
 		goto error;
 	}
 
-	key = lookup_user_key(NULL, id, 0, 0, 0);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 0, 0, 0);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error2;
 	}
 
-	ret = key_unlink(keyring, key);
+	ret = key_unlink(key_ref_to_ptr(keyring_ref), key_ref_to_ptr(key_ref));
 
-	key_put(key);
+	key_ref_put(key_ref);
  error2:
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error:
 	return ret;
 
···
 			 size_t buflen)
 {
 	struct key *key, *instkey;
+	key_ref_t key_ref;
 	char *tmpbuf;
 	long ret;
 
-	key = lookup_user_key(NULL, keyid, 0, 1, KEY_VIEW);
-	if (IS_ERR(key)) {
+	key_ref = lookup_user_key(NULL, keyid, 0, 1, KEY_VIEW);
+	if (IS_ERR(key_ref)) {
 		/* viewing a key under construction is permitted if we have the
 		 * authorisation token handy */
-		if (PTR_ERR(key) == -EACCES) {
+		if (PTR_ERR(key_ref) == -EACCES) {
 			instkey = key_get_instantiation_authkey(keyid);
 			if (!IS_ERR(instkey)) {
 				key_put(instkey);
-				key = lookup_user_key(NULL, keyid, 0, 1, 0);
-				if (!IS_ERR(key))
+				key_ref = lookup_user_key(NULL, keyid,
+							  0, 1, 0);
+				if (!IS_ERR(key_ref))
 					goto okay;
 			}
 		}
 
-		ret = PTR_ERR(key);
+		ret = PTR_ERR(key_ref);
 		goto error;
 	}
 
···
 	if (!tmpbuf)
 		goto error2;
 
+	key = key_ref_to_ptr(key_ref);
+
 	ret = snprintf(tmpbuf, PAGE_SIZE - 1,
-		       "%s;%d;%d;%06x;%s",
-		       key->type->name,
-		       key->uid,
-		       key->gid,
-		       key->perm,
-		       key->description ? key->description :""
+		       "%s;%d;%d;%08x;%s",
+		       key_ref_to_ptr(key_ref)->type->name,
+		       key_ref_to_ptr(key_ref)->uid,
+		       key_ref_to_ptr(key_ref)->gid,
+		       key_ref_to_ptr(key_ref)->perm,
+		       key_ref_to_ptr(key_ref)->description ?
+		       key_ref_to_ptr(key_ref)->description : ""
 		       );
 
 	/* include a NUL char at the end of the data */
···
 
 	kfree(tmpbuf);
  error2:
-	key_put(key);
+	key_ref_put(key_ref);
  error:
 	return ret;
 
···
 			   key_serial_t destringid)
 {
 	struct key_type *ktype;
-	struct key *keyring, *key, *dest;
+	key_ref_t keyring_ref, key_ref, dest_ref;
 	char type[32], *description;
 	long dlen, ret;
 
···
 		goto error2;
 
 	/* get the keyring at which to begin the search */
-	keyring = lookup_user_key(NULL, ringid, 0, 0, KEY_SEARCH);
-	if (IS_ERR(keyring)) {
-		ret = PTR_ERR(keyring);
+	keyring_ref = lookup_user_key(NULL, ringid, 0, 0, KEY_SEARCH);
+	if (IS_ERR(keyring_ref)) {
+		ret = PTR_ERR(keyring_ref);
 		goto error2;
 	}
 
 	/* get the destination keyring if specified */
-	dest = NULL;
+	dest_ref = NULL;
 	if (destringid) {
-		dest = lookup_user_key(NULL, destringid, 1, 0, KEY_WRITE);
-		if (IS_ERR(dest)) {
-			ret = PTR_ERR(dest);
+		dest_ref = lookup_user_key(NULL, destringid, 1, 0, KEY_WRITE);
+		if (IS_ERR(dest_ref)) {
+			ret = PTR_ERR(dest_ref);
 			goto error3;
 		}
 	}
···
 	}
 
 	/* do the search */
-	key = keyring_search(keyring, ktype, description);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = keyring_search(keyring_ref, ktype, description);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 
 		/* treat lack or presence of a negative key the same */
 		if (ret == -EAGAIN)
···
 	}
 
 	/* link the resulting key to the destination keyring if we can */
-	if (dest) {
+	if (dest_ref) {
 		ret = -EACCES;
-		if (!key_permission(key, KEY_LINK))
+		if (!key_permission(key_ref, KEY_LINK))
 			goto error6;
 
-		ret = key_link(dest, key);
+		ret = key_link(key_ref_to_ptr(dest_ref), key_ref_to_ptr(key_ref));
 		if (ret < 0)
 			goto error6;
 	}
 
-	ret = key->serial;
+	ret = key_ref_to_ptr(key_ref)->serial;
 
  error6:
-	key_put(key);
+	key_ref_put(key_ref);
  error5:
 	key_type_put(ktype);
  error4:
-	key_put(dest);
+	key_ref_put(dest_ref);
  error3:
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error2:
 	kfree(description);
  error:
 	return ret;
 
 } /* end keyctl_keyring_search() */
-
-/*****************************************************************************/
-/*
- * see if the key we're looking at is the target key
- */
-static int keyctl_read_key_same(const struct key *key, const void *target)
-{
-	return key == target;
-
-} /* end keyctl_read_key_same() */
 
 /*****************************************************************************/
 /*
···
  */
 long keyctl_read_key(key_serial_t keyid, char __user *buffer, size_t buflen)
 {
-	struct key *key, *skey;
+	struct key *key;
+	key_ref_t key_ref;
 	long ret;
 
 	/* find the key first */
-	key = lookup_user_key(NULL, keyid, 0, 0, 0);
-	if (!IS_ERR(key)) {
-		/* see if we can read it directly */
-		if (key_permission(key, KEY_READ))
-			goto can_read_key;
+	key_ref = lookup_user_key(NULL, keyid, 0, 0, 0);
+	if (IS_ERR(key_ref)) {
+		ret = -ENOKEY;
+		goto error;
+	}
 
-		/* we can't; see if it's searchable from this process's
-		 * keyrings
-		 * - we automatically take account of the fact that it may be
-		 *   dangling off an instantiation key
-		 */
-		skey = search_process_keyrings(key->type, key,
-					       keyctl_read_key_same, current);
-		if (!IS_ERR(skey))
-			goto can_read_key2;
+	key = key_ref_to_ptr(key_ref);
 
-		ret = PTR_ERR(skey);
-		if (ret == -EAGAIN)
-			ret = -EACCES;
+	/* see if we can read it directly */
+	if (key_permission(key_ref, KEY_READ))
+		goto can_read_key;
+
+	/* we can't; see if it's searchable from this process's keyrings
+	 * - we automatically take account of the fact that it may be
+	 *   dangling off an instantiation key
+	 */
+	if (!is_key_possessed(key_ref)) {
+		ret = -EACCES;
 		goto error2;
 	}
 
-	ret = -ENOKEY;
-	goto error;
-
 	/* the key is probably readable - now try to read it */
- can_read_key2:
-	key_put(skey);
  can_read_key:
 	ret = key_validate(key);
 	if (ret == 0) {
···
 long keyctl_chown_key(key_serial_t id, uid_t uid, gid_t gid)
 {
 	struct key *key;
+	key_ref_t key_ref;
 	long ret;
 
 	ret = 0;
 	if (uid == (uid_t) -1 && gid == (gid_t) -1)
 		goto error;
 
-	key = lookup_user_key(NULL, id, 1, 1, 0);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 1, 1, 0);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error;
 	}
+
+	key = key_ref_to_ptr(key_ref);
 
 	/* make the changes with the locks held to prevent chown/chown races */
 	ret = -EACCES;
···
 long keyctl_setperm_key(key_serial_t id, key_perm_t perm)
 {
 	struct key *key;
+	key_ref_t key_ref;
 	long ret;
 
 	ret = -EINVAL;
-	if (perm & ~(KEY_USR_ALL | KEY_GRP_ALL | KEY_OTH_ALL))
+	if (perm & ~(KEY_POS_ALL | KEY_USR_ALL | KEY_GRP_ALL | KEY_OTH_ALL))
 		goto error;
 
-	key = lookup_user_key(NULL, id, 1, 1, 0);
-	if (IS_ERR(key)) {
-		ret = PTR_ERR(key);
+	key_ref = lookup_user_key(NULL, id, 1, 1, 0);
+	if (IS_ERR(key_ref)) {
+		ret = PTR_ERR(key_ref);
 		goto error;
 	}
+
+	key = key_ref_to_ptr(key_ref);
 
 	/* make the changes with the locks held to prevent chown/chmod races */
 	ret = -EACCES;
···
 			    key_serial_t ringid)
 {
 	struct request_key_auth *rka;
-	struct key *instkey, *keyring;
+	struct key *instkey;
+	key_ref_t keyring_ref;
 	void *payload;
 	long ret;
 
···
 
 	/* find the destination keyring amongst those belonging to the
 	 * requesting task */
-	keyring = NULL;
+	keyring_ref = NULL;
 	if (ringid) {
-		keyring = lookup_user_key(rka->context, ringid, 1, 0,
-					  KEY_WRITE);
-		if (IS_ERR(keyring)) {
-			ret = PTR_ERR(keyring);
+		keyring_ref = lookup_user_key(rka->context, ringid, 1, 0,
+					      KEY_WRITE);
+		if (IS_ERR(keyring_ref)) {
+			ret = PTR_ERR(keyring_ref);
 			goto error3;
 		}
 	}
 
 	/* instantiate the key and link it into a keyring */
 	ret = key_instantiate_and_link(rka->target_key, payload, plen,
-				       keyring, instkey);
+				       key_ref_to_ptr(keyring_ref), instkey);
 
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error3:
 	key_put(instkey);
  error2:
···
 long keyctl_negate_key(key_serial_t id, unsigned timeout, key_serial_t ringid)
 {
 	struct request_key_auth *rka;
-	struct key *instkey, *keyring;
+	struct key *instkey;
+	key_ref_t keyring_ref;
 	long ret;
 
 	/* find the instantiation authorisation key */
···
 
 	/* find the destination keyring if present (which must also be
 	 * writable) */
-	keyring = NULL;
+	keyring_ref = NULL;
 	if (ringid) {
-		keyring = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
-		if (IS_ERR(keyring)) {
-			ret = PTR_ERR(keyring);
+		keyring_ref = lookup_user_key(NULL, ringid, 1, 0, KEY_WRITE);
+		if (IS_ERR(keyring_ref)) {
+			ret = PTR_ERR(keyring_ref);
 			goto error2;
 		}
 	}
 
 	/* instantiate the key and link it into a keyring */
-	ret = key_negate_and_link(rka->target_key, timeout, keyring, instkey);
+	ret = key_negate_and_link(rka->target_key, timeout,
+				  key_ref_to_ptr(keyring_ref), instkey);
 
-	key_put(keyring);
+	key_ref_put(keyring_ref);
  error2:
 	key_put(instkey);
  error:

security/keys/keyring.c

···
 	int ret;
 
 	keyring = key_alloc(&key_type_keyring, description,
-			    uid, gid, KEY_USR_ALL, not_in_quota);
+			    uid, gid, KEY_POS_ALL | KEY_USR_ALL, not_in_quota);
 
 	if (!IS_ERR(keyring)) {
 		ret = key_instantiate_and_link(keyring, NULL, 0, dest, NULL);
···
  * - we rely on RCU to prevent the keyring lists from disappearing on us
  * - we return -EAGAIN if we didn't find any matching key
  * - we return -ENOKEY if we only found negative matching keys
+ * - we propagate the possession attribute from the keyring ref to the key ref
  */
-struct key *keyring_search_aux(struct key *keyring,
-			       struct task_struct *context,
-			       struct key_type *type,
-			       const void *description,
-			       key_match_func_t match)
+key_ref_t keyring_search_aux(key_ref_t keyring_ref,
+			     struct task_struct *context,
+			     struct key_type *type,
+			     const void *description,
+			     key_match_func_t match)
 {
 	struct {
 		struct keyring_list *keylist;
···
 
 	struct keyring_list *keylist;
 	struct timespec now;
-	struct key *key;
+	unsigned long possessed;
+	struct key *keyring, *key;
+	key_ref_t key_ref;
 	long err;
 	int sp, kix;
 
+	keyring = key_ref_to_ptr(keyring_ref);
+	possessed = is_key_possessed(keyring_ref);
 	key_check(keyring);
 
-	rcu_read_lock();
-
 	/* top keyring must have search permission to begin the search */
-	key = ERR_PTR(-EACCES);
-	if (!key_task_permission(keyring, context, KEY_SEARCH))
+	key_ref = ERR_PTR(-EACCES);
+	if (!key_task_permission(keyring_ref, context, KEY_SEARCH))
 		goto error;
 
-	key = ERR_PTR(-ENOTDIR);
+	key_ref = ERR_PTR(-ENOTDIR);
 	if (keyring->type != &key_type_keyring)
 		goto error;
+
+	rcu_read_lock();
 
 	now = current_kernel_time();
 	err = -EAGAIN;
 	sp = 0;
 
 	/* start processing a new keyring */
- descend:
+descend:
 	if (test_bit(KEY_FLAG_REVOKED, &keyring->flags))
 		goto not_this_keyring;
 
···
 			continue;
 
 		/* key must have search permissions */
-		if (!key_task_permission(key, context, KEY_SEARCH))
+		if (!key_task_permission(make_key_ref(key, possessed),
+					 context, KEY_SEARCH))
 			continue;
 
 		/* we set a different error code if we find a negative key */
···
 
 	/* search through the keyrings nested in this one */
 	kix = 0;
- ascend:
+ascend:
 	for (; kix < keylist->nkeys; kix++) {
 		key = keylist->keys[kix];
 		if (key->type != &key_type_keyring)
···
 		if (sp >= KEYRING_SEARCH_MAX_DEPTH)
 			continue;
 
-		if (!key_task_permission(key, context, KEY_SEARCH))
+		if (!key_task_permission(make_key_ref(key, possessed),
+					 context, KEY_SEARCH))
 			continue;
 
 		/* stack the current position */
···
 
 	/* the keyring we're looking at was disqualified or didn't contain a
 	 * matching key */
- not_this_keyring:
+not_this_keyring:
 	if (sp > 0) {
 		/* resume the processing of a keyring higher up in the tree */
 		sp--;
···
 		goto ascend;
 	}
 
-	key = ERR_PTR(err);
-	goto error;
+	key_ref = ERR_PTR(err);
+	goto error_2;
 
 	/* we found a viable match */
- found:
+found:
 	atomic_inc(&key->usage);
 	key_check(key);
- error:
+	key_ref = make_key_ref(key, possessed);
+error_2:
 	rcu_read_unlock();
-	return key;
+error:
+	return key_ref;
 
 } /* end keyring_search_aux() */
 
···
  * - we return -EAGAIN if we didn't find any matching key
  * - we return -ENOKEY if we only found negative matching keys
  */
-struct key *keyring_search(struct key *keyring,
-			   struct key_type *type,
-			   const char *description)
+key_ref_t keyring_search(key_ref_t keyring,
+			 struct key_type *type,
+			 const char *description)
 {
 	if (!type->match)
 		return ERR_PTR(-ENOKEY);
···
  * search the given keyring only (no recursion)
  * - keyring must be locked by caller
  */
-struct key *__keyring_search_one(struct key *keyring,
-				 const struct key_type *ktype,
-				 const char *description,
-				 key_perm_t perm)
+key_ref_t __keyring_search_one(key_ref_t keyring_ref,
+			       const struct key_type *ktype,
+			       const char *description,
+			       key_perm_t perm)
 {
 	struct keyring_list *klist;
-	struct key *key;
+	unsigned long possessed;
+	struct key *keyring, *key;
 	int loop;
+
+	keyring = key_ref_to_ptr(keyring_ref);
+	possessed = is_key_possessed(keyring_ref);
 
 	rcu_read_lock();
 
···
 			if (key->type == ktype &&
 			    (!key->type->match ||
 			     key->type->match(key, description)) &&
-			    key_permission(key, perm) &&
+			    key_permission(make_key_ref(key, possessed),
+					   perm) &&
 			    !test_bit(KEY_FLAG_REVOKED, &key->flags)
 			    )
 				goto found;
 		}
 	}
 
-	key = ERR_PTR(-ENOKEY);
-	goto error;
+	rcu_read_unlock();
+	return ERR_PTR(-ENOKEY);
 
  found:
 	atomic_inc(&key->usage);
- error:
 	rcu_read_unlock();
-	return key;
+	return make_key_ref(key, possessed);
 
 } /* end __keyring_search_one() */
 
···
 			if (strcmp(keyring->description, name) != 0)
 				continue;
 
-			if (!key_permission(keyring, KEY_SEARCH))
+			if (!key_permission(make_key_ref(keyring, 0),
+					    KEY_SEARCH))
 				continue;
 
 			/* found a potential candidate, but we still need to

security/keys/proc.c

···
 #define showflag(KEY, LETTER, FLAG) \
 	(test_bit(FLAG,	&(KEY)->flags) ? LETTER : '-')
 
-	seq_printf(m, "%08x %c%c%c%c%c%c %5d %4s %06x %5d %5d %-9.9s ",
+	seq_printf(m, "%08x %c%c%c%c%c%c %5d %4s %08x %5d %5d %-9.9s ",
 		   key->serial,
 		   showflag(key, 'I', KEY_FLAG_INSTANTIATED),
 		   showflag(key, 'R', KEY_FLAG_REVOKED),

security/keys/process_keys.c

···
 	.type		= &key_type_keyring,
 	.user		= &root_key_user,
 	.sem		= __RWSEM_INITIALIZER(root_user_keyring.sem),
-	.perm		= KEY_USR_ALL,
+	.perm		= KEY_POS_ALL | KEY_USR_ALL,
 	.flags		= 1 << KEY_FLAG_INSTANTIATED,
 	.description	= "_uid.0",
 #ifdef KEY_DEBUGGING
···
 	.type		= &key_type_keyring,
 	.user		= &root_key_user,
 	.sem		= __RWSEM_INITIALIZER(root_session_keyring.sem),
-	.perm		= KEY_USR_ALL,
+	.perm		= KEY_POS_ALL | KEY_USR_ALL,
 	.flags		= 1 << KEY_FLAG_INSTANTIATED,
 	.description	= "_uid_ses.0",
 #ifdef KEY_DEBUGGING
···
 	user->session_keyring = session_keyring;
 	ret = 0;
 
- error:
+error:
 	return ret;
 
 } /* end alloc_uid_keyring() */
···
 	ret = 0;
 
 	key_put(old);
- error:
+error:
 	return ret;
 
 } /* end install_thread_keyring() */
···
 	}
 
 	ret = 0;
- error:
+error:
 	return ret;
 
 } /* end install_process_keyring() */
···
 	/* we're using RCU on the pointer */
 	synchronize_rcu();
 	key_put(old);
- error:
+error:
 	return ret;
 
 } /* end install_session_keyring() */
···
  * - we return -EAGAIN if we didn't find any matching key
  * - we return -ENOKEY if we found only negative matching keys
  */
-struct key *search_process_keyrings(struct key_type *type,
-				    const void *description,
-				    key_match_func_t match,
-				    struct task_struct *context)
+key_ref_t search_process_keyrings(struct key_type *type,
+				  const void *description,
+				  key_match_func_t match,
+				  struct task_struct *context)
 {
 	struct request_key_auth *rka;
-	struct key *key, *ret, *err, *instkey;
+	key_ref_t key_ref, ret, err, instkey_ref;
 
 	/* we want to return -EAGAIN or -ENOKEY if any of the keyrings were
 	 * searchable, but we failed to find a key or we found a negative key;
···
 	 *
 	 * in terms of priority: success > -ENOKEY > -EAGAIN > other error
 	 */
-	key = NULL;
+	key_ref = NULL;
 	ret = NULL;
 	err = ERR_PTR(-EAGAIN);
 
 	/* search the thread keyring first */
 	if (context->thread_keyring) {
-		key = keyring_search_aux(context->thread_keyring,
-					 context, type, description, match);
-		if (!IS_ERR(key))
+		key_ref = keyring_search_aux(
+			make_key_ref(context->thread_keyring, 1),
+			context, type, description, match);
+		if (!IS_ERR(key_ref))
 			goto found;
 
-		switch (PTR_ERR(key)) {
+		switch (PTR_ERR(key_ref)) {
 		case -EAGAIN: /* no key */
 			if (ret)
 				break;
 		case -ENOKEY: /* negative key */
-			ret = key;
+			ret = key_ref;
 			break;
 		default:
-			err = key;
+			err = key_ref;
 			break;
 		}
 	}
 
 	/* search the process keyring second */
 	if (context->signal->process_keyring) {
-		key = keyring_search_aux(context->signal->process_keyring,
-					 context, type, description, match);
-		if (!IS_ERR(key))
+		key_ref = keyring_search_aux(
+			make_key_ref(context->signal->process_keyring, 1),
+			context, type, description, match);
+		if (!IS_ERR(key_ref))
 			goto found;
 
-		switch (PTR_ERR(key)) {
+		switch (PTR_ERR(key_ref)) {
 		case -EAGAIN: /* no key */
 			if (ret)
 				break;
 		case -ENOKEY: /* negative key */
-			ret = key;
+			ret = key_ref;
 			break;
 		default:
-			err = key;
+			err = key_ref;
 			break;
 		}
 	}
···
 	/* search the session keyring */
 	if (context->signal->session_keyring) {
 		rcu_read_lock();
-		key = keyring_search_aux(
-			rcu_dereference(context->signal->session_keyring),
+		key_ref = keyring_search_aux(
+			make_key_ref(rcu_dereference(
+					     context->signal->session_keyring),
+				     1),
 			context, type, description, match);
 		rcu_read_unlock();
 
-		if (!IS_ERR(key))
+		if (!IS_ERR(key_ref))
 			goto found;
 
-		switch (PTR_ERR(key)) {
+		switch (PTR_ERR(key_ref)) {
 		case -EAGAIN: /* no key */
 			if (ret)
 				break;
 		case -ENOKEY: /* negative key */
-			ret = key;
+			ret = key_ref;
 			break;
 		default:
-			err = key;
+			err = key_ref;
 			break;
 		}
 
···
 			goto no_key;
 
 		rcu_read_lock();
-		instkey = __keyring_search_one(
-			rcu_dereference(context->signal->session_keyring),
+		instkey_ref = __keyring_search_one(
+			make_key_ref(rcu_dereference(
+					     context->signal->session_keyring),
+				     1),
 			&key_type_request_key_auth, NULL, 0);
 		rcu_read_unlock();
 
-		if (IS_ERR(instkey))
+		if (IS_ERR(instkey_ref))
 			goto no_key;
 
-		rka = instkey->payload.data;
+		rka = key_ref_to_ptr(instkey_ref)->payload.data;
 
-		key = search_process_keyrings(type, description, match,
-					      rka->context);
-		key_put(instkey);
+		key_ref = search_process_keyrings(type, description, match,
+						  rka->context);
+		key_ref_put(instkey_ref);
 
-		if (!IS_ERR(key))
+		if (!IS_ERR(key_ref))
 			goto found;
 
-		switch (PTR_ERR(key)) {
+		switch (PTR_ERR(key_ref)) {
 		case -EAGAIN: /* no key */
 			if (ret)
 				break;
 		case -ENOKEY: /* negative key */
-			ret = key;
+			ret = key_ref;
 			break;
 		default:
-			err = key;
+			err = key_ref;
 			break;
 		}
 	}
 	/* or search the user-session keyring */
 	else {
-		key = keyring_search_aux(context->user->session_keyring,
-					 context, type, description, match);
-		if (!IS_ERR(key))
+		key_ref = keyring_search_aux(
+			make_key_ref(context->user->session_keyring, 1),
+			context, type, description, match);
+		if (!IS_ERR(key_ref))
 			goto found;
 
-		switch (PTR_ERR(key)) {
+		switch (PTR_ERR(key_ref)) {
 		case -EAGAIN: /* no key */
 			if (ret)
 				break;
 		case -ENOKEY: /* negative key */
-			ret = key;
+			ret = key_ref;
 			break;
 		default:
-			err = key;
+			err = key_ref;
 			break;
 		}
 	}
···
 
 no_key:
 	/* no key - decide on the error we're going to go for */
-	key = ret ? ret : err;
+	key_ref = ret ? ret : err;
 
 found:
-	return key;
+	return key_ref;
 
 } /* end search_process_keyrings() */
+
+/*****************************************************************************/
+/*
+ * see if the key we're looking at is the target key
+ */
+static int lookup_user_key_possessed(const struct key *key, const void *target)
+{
+	return key == target;
+
+} /* end lookup_user_key_possessed() */
 
 /*****************************************************************************/
 /*
···
  * - don't create special keyrings unless so requested
  * - partially constructed keys aren't found unless requested
  */
-struct key *lookup_user_key(struct task_struct *context, key_serial_t id,
-			    int create, int partial, key_perm_t perm)
+key_ref_t lookup_user_key(struct task_struct *context, key_serial_t id,
+			  int create, int partial, key_perm_t perm)
 {
+	key_ref_t key_ref, skey_ref;
 	struct key *key;
 	int ret;
 
 	if (!context)
 		context = current;
 
-	key = ERR_PTR(-ENOKEY);
+	key_ref = ERR_PTR(-ENOKEY);
 
 	switch (id) {
 	case KEY_SPEC_THREAD_KEYRING:
···
 
 		key = context->thread_keyring;
 		atomic_inc(&key->usage);
+		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_PROCESS_KEYRING:
···
 
 		key = context->signal->process_keyring;
 		atomic_inc(&key->usage);
+		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_SESSION_KEYRING:
···
 			/* always install a session keyring upon access if one
 			 * doesn't exist yet */
 			ret = install_session_keyring(
-			       context, context->user->session_keyring);
+				context, context->user->session_keyring);
 			if (ret < 0)
 				goto error;
 		}
···
 		key = rcu_dereference(context->signal->session_keyring);
 		atomic_inc(&key->usage);
 		rcu_read_unlock();
+		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_USER_KEYRING:
 		key = context->user->uid_keyring;
 		atomic_inc(&key->usage);
+		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_USER_SESSION_KEYRING:
 		key = context->user->session_keyring;
 		atomic_inc(&key->usage);
+		key_ref = make_key_ref(key, 1);
 		break;
 
 	case KEY_SPEC_GROUP_KEYRING:
···
 		goto error;
 
 	default:
-		key = ERR_PTR(-EINVAL);
+		key_ref = ERR_PTR(-EINVAL);
 		if (id < 1)
 			goto error;
 
 		key = key_lookup(id);
-		if (IS_ERR(key))
+		if (IS_ERR(key)) {
+			key_ref = ERR_PTR(PTR_ERR(key));
 			goto error;
+		}
+
+		key_ref = make_key_ref(key, 0);
+
+		/* check to see if we possess the key */
+		skey_ref = search_process_keyrings(key->type, key,
+						   lookup_user_key_possessed,
+						   current);
+
+		if (!IS_ERR(skey_ref)) {
+			key_put(key);
+			key_ref = skey_ref;
+		}
+
 		break;
 	}
 
···
 	/* check the permissions */
 	ret = -EACCES;
 
-	if (!key_task_permission(key, context, perm))
+	if (!key_task_permission(key_ref, context, perm))
 		goto invalid_key;
 
- error:
-	return key;
+error:
+	return key_ref;
 
- invalid_key:
-	key_put(key);
-	key = ERR_PTR(ret);
+invalid_key:
+	key_ref_put(key_ref);
+	key_ref = ERR_PTR(ret);
 	goto error;
 
 } /* end lookup_user_key() */
···
 	ret = keyring->serial;
 	key_put(keyring);
 
- error2:
+error2:
 	up(&key_session_sem);
- error:
+error:
 	return ret;
 
 } /* end join_session_keyring() */

security/keys/request_key.c

···
 
 	/* create a key and add it to the queue */
 	key = key_alloc(type, description,
-			current->fsuid, current->fsgid, KEY_USR_ALL, 0);
+			current->fsuid, current->fsgid, KEY_POS_ALL, 0);
 	if (IS_ERR(key))
 		goto alloc_failed;
 
···
 {
 	struct key_user *user;
 	struct key *key;
+	key_ref_t key_ref;
 
 	kenter("%s,%s,%s,%p",
 	       type->name, description, callout_info, dest_keyring);
 
 	/* search all the process keyrings for a key */
-	key = search_process_keyrings(type, description, type->match, current);
+	key_ref = search_process_keyrings(type, description, type->match,
+					  current);
 
-	if (PTR_ERR(key) == -EAGAIN) {
+	kdebug("search 1: %p", key_ref);
+
+	if (!IS_ERR(key_ref)) {
+		key = key_ref_to_ptr(key_ref);
+	}
+	else if (PTR_ERR(key_ref) != -EAGAIN) {
+		key = ERR_PTR(PTR_ERR(key_ref));
+	}
+	else  {
 		/* the search failed, but the keyrings were searchable, so we
 		 * should consult userspace if we can */
 		key = ERR_PTR(-ENOKEY);
···
 		if (!user)
 			goto nomem;
 
-		do {
+		for (;;) {
 			if (signal_pending(current))
 				goto interrupted;
 
···
 
 			/* someone else made the key we want, so we need to
 			 * search again as it might now be available to us */
-			key = search_process_keyrings(type, description,
-						      type->match, current);
+			key_ref = search_process_keyrings(type, description,
+							  type->match,
+							  current);
 
-		} while (PTR_ERR(key) == -EAGAIN);
+			kdebug("search 2: %p", key_ref);
+
+			if (!IS_ERR(key_ref)) {
+				key = key_ref_to_ptr(key_ref);
+				break;
+			}
+
+			if (PTR_ERR(key_ref) != -EAGAIN) {
+				key = ERR_PTR(PTR_ERR(key_ref));
+				break;
+			}
+		}
 
 		key_user_put(user);
 

security/keys/request_key_auth.c

···
 
 	rkakey = key_alloc(&key_type_request_key_auth, desc,
 			   current->fsuid, current->fsgid,
-			   KEY_USR_VIEW, 1);
+			   KEY_POS_VIEW | KEY_USR_VIEW, 1);
 	if (IS_ERR(rkakey)) {
 		key_put(keyring);
 		kleave("= %ld", PTR_ERR(rkakey));