HID: hidraw: add HIDIOCREVOKE ioctl

There is a need for userspace applications to open HID devices directly.
Use-cases include configuration of gaming mice or direct access to
joystick devices. The latter is currently handled by the uaccess tag in
systemd, other devices include more custom/local configurations or just
sudo.

A better approach is what we already have for evdev devices: give the
application a file descriptor and revoke it when it may no longer access
that device.

This patch is the hidraw equivalent to the EVIOCREVOKE ioctl, see
commit c7dc65737c9a ("Input: evdev - add EVIOCREVOKE ioctl") for full
details.

An MR for systemd-logind has been filed here:
https://github.com/systemd/systemd/pull/33970

Signed-off-by: Peter Hutterer <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Benjamin Tissoires <[e-mail]>

drivers/hid/hidraw.c

···
 static struct hidraw *hidraw_table[HIDRAW_MAX_DEVICES];
 static DECLARE_RWSEM(minors_rwsem);
 
+static inline bool hidraw_is_revoked(struct hidraw_list *list)
+{
+	return list->revoked;
+}
+
 static ssize_t hidraw_read(struct file *file, char __user *buffer, size_t count, loff_t *ppos)
 {
 	struct hidraw_list *list = file->private_data;
 	int ret = 0, len;
 	DECLARE_WAITQUEUE(wait, current);
+
+	if (hidraw_is_revoked(list))
+		return -ENODEV;
 
 	mutex_lock(&list->read_mutex);
 
···
 
 static ssize_t hidraw_write(struct file *file, const char __user *buffer, size_t count, loff_t *ppos)
 {
+	struct hidraw_list *list = file->private_data;
 	ssize_t ret;
 	down_read(&minors_rwsem);
-	ret = hidraw_send_report(file, buffer, count, HID_OUTPUT_REPORT);
+	if (hidraw_is_revoked(list))
+		ret = -ENODEV;
+	else
+		ret = hidraw_send_report(file, buffer, count, HID_OUTPUT_REPORT);
 	up_read(&minors_rwsem);
 	return ret;
 }
···
 	poll_wait(file, &list->hidraw->wait, wait);
 	if (list->head != list->tail)
 		mask |= EPOLLIN | EPOLLRDNORM;
-	if (!list->hidraw->exist)
+	if (!list->hidraw->exist || hidraw_is_revoked(list))
 		mask |= EPOLLERR | EPOLLHUP;
 	return mask;
 }
···
 {
 	struct hidraw_list *list = file->private_data;
 
+	if (hidraw_is_revoked(list))
+		return -ENODEV;
+
 	return fasync_helper(fd, file, on, &list->fasync);
 }
 
···
 	return 0;
 }
 
+static int hidraw_revoke(struct hidraw_list *list)
+{
+	list->revoked = true;
+
+	return 0;
+}
+
 static long hidraw_ioctl(struct file *file, unsigned int cmd,
 							unsigned long arg)
 {
···
 	unsigned int minor = iminor(inode);
 	long ret = 0;
 	struct hidraw *dev;
+	struct hidraw_list *list = file->private_data;
 	void __user *user_arg = (void __user*) arg;
 
 	down_read(&minors_rwsem);
 	dev = hidraw_table[minor];
-	if (!dev || !dev->exist) {
+	if (!dev || !dev->exist || hidraw_is_revoked(list)) {
 		ret = -ENODEV;
 		goto out;
 	}
···
 				dinfo.product = dev->hid->product;
 				if (copy_to_user(user_arg, &dinfo, sizeof(dinfo)))
 					ret = -EFAULT;
+				break;
+			}
+		case HIDIOCREVOKE:
+			{
+				if (user_arg)
+					ret = -EINVAL;
+				else
+					ret = hidraw_revoke(list);
 				break;
 			}
 		default:
···
 	list_for_each_entry(list, &dev->list, node) {
 		int new_head = (list->head + 1) & (HIDRAW_BUFFER_SIZE - 1);
 
-		if (new_head == list->tail)
+		if (hidraw_is_revoked(list) || new_head == list->tail)
 			continue;
 
 		if (!(list->buffer[list->head].value = kmemdup(data, len, GFP_ATOMIC))) {

include/linux/hidraw.h

···
 	struct hidraw *hidraw;
 	struct list_head node;
 	struct mutex read_mutex;
+	bool revoked;
 };
 
 #ifdef CONFIG_HIDRAW

include/uapi/linux/hidraw.h

···
 /* The first byte of SOUTPUT and GOUTPUT is the report number */
 #define HIDIOCSOUTPUT(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x0B, len)
 #define HIDIOCGOUTPUT(len)    _IOC(_IOC_WRITE|_IOC_READ, 'H', 0x0C, len)
+#define HIDIOCREVOKE	      _IOW('H', 0x0D, int) /* Revoke device access */
 
 #define HIDRAW_FIRST_MINOR 0
 #define HIDRAW_MAX_DEVICES 64