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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: Siddh Raman Pant <code@siddh.me>
Acked-by: David Howells <dhowells@redhat.com>
Message-Id: <20230605143616.640517-1-code@siddh.me>
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Siddh Raman Pant 2023-06-05 20:06:16 +05:30 committed by Christian Brauner
parent a7bc2e8ddf
commit 943211c874
2 changed files with 7 additions and 8 deletions
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3
include/linux/watch_queue.h
View File

@ -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 */
};
/*

12
kernel/watch_queue.c
View File

@ -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);