Commit 943211c8 authored by Siddh Raman Pant's avatar Siddh Raman Pant Committed by Christian Brauner
Browse files

watch_queue: prevent dangling pipe pointer 



NULL the dangling pipe reference while clearing watch_queue.

If not done, a reference to a freed pipe remains in the watch_queue,
as this function is called before freeing a pipe in free_pipe_info()
(see line 834 of fs/pipe.c).

The sole use of wqueue->defunct is for checking if the watch queue has
been cleared, but wqueue->pipe is also NULLed while clearing.

Thus, wqueue->defunct is superfluous, as wqueue->pipe can be checked
for NULL. Hence, the former can be removed.

Tested with keyutils testsuite.

Cc: stable@vger.kernel.org # 6.1
Signed-off-by: default avatarSiddh Raman Pant <code@siddh.me>
Acked-by: default avatarDavid Howells <dhowells@redhat.com>
Message-Id: <20230605143616.640517-1-code@siddh.me>
Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parent a7bc2e8d

include/linux/watch_queue.h

+1 −2
Original line number Diff line number Diff line
@@ -38,7 +38,7 @@ struct watch_filter { 
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 pipe_inode_info	*pipe;		/* Pipe we use as a buffer, NULL if queue closed */

	struct hlist_head	watches;	/* Contributory watches */

	struct page		**notes;	/* Preallocated notifications */

	unsigned long		*notes_bitmap;	/* Allocation bitmap for notes */
@@ -46,7 +46,6 @@ struct watch_queue { 
	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 */

};



/*

kernel/watch_queue.c

+6 −6
Original line number Diff line number Diff line
@@ -42,7 +42,7 @@ MODULE_AUTHOR("Red Hat, Inc."); 
static inline bool lock_wqueue(struct watch_queue *wqueue)

{

	spin_lock_bh(&wqueue->lock);

	if (unlikely(wqueue->defunct)) {

	if (unlikely(!wqueue->pipe)) {

		spin_unlock_bh(&wqueue->lock);

		return false;

	}
@@ -104,9 +104,6 @@ static bool post_one_notification(struct watch_queue *wqueue, 
	unsigned int head, tail, mask, note, offset, len;

	bool done = false;



	if (!pipe)

		return false;



	spin_lock_irq(&pipe->rd_wait.lock);



	mask = pipe->ring_size - 1;
@@ -603,8 +600,11 @@ void watch_queue_clear(struct watch_queue *wqueue) 
	rcu_read_lock();

	spin_lock_bh(&wqueue->lock);



	/* Prevent new notifications from being stored. */

	wqueue->defunct = true;

	/*

	 * This pipe can be freed by callers like free_pipe_info().

	 * Removing this reference also prevents new notifications.

	 */

	wqueue->pipe = NULL;



	while (!hlist_empty(&wqueue->watches)) {

		watch = hlist_entry(wqueue->watches.first, struct watch, queue_node);