Patch "watch_queue: prevent dangling pipe pointer" has been added to the 6.1-stable tree

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This is a note to let you know that I've just added the patch titled

    watch_queue: prevent dangling pipe pointer

to the 6.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     watch_queue-prevent-dangling-pipe-pointer.patch
and it can be found in the queue-6.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.


>From 943211c87427f25bd22e0e63849fb486bb5f87fa Mon Sep 17 00:00:00 2001
From: Siddh Raman Pant <code@xxxxxxxx>
Date: Mon, 5 Jun 2023 20:06:16 +0530
Subject: watch_queue: prevent dangling pipe pointer

From: Siddh Raman Pant <code@xxxxxxxx>

commit 943211c87427f25bd22e0e63849fb486bb5f87fa upstream.

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@xxxxxxxxxxxxxxx # 6.1
Signed-off-by: Siddh Raman Pant <code@xxxxxxxx>
Acked-by: David Howells <dhowells@xxxxxxxxxx>
Message-Id: <20230605143616.640517-1-code@xxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/watch_queue.h |    3 +--
 kernel/watch_queue.c        |   12 ++++++------
 2 files changed, 7 insertions(+), 8 deletions(-)

--- a/include/linux/watch_queue.h
+++ b/include/linux/watch_queue.h
@@ -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 */
 };
 
 /*
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -43,7 +43,7 @@ MODULE_LICENSE("GPL");
 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;
 	}
@@ -105,9 +105,6 @@ static bool post_one_notification(struct
 	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;
@@ -604,8 +601,11 @@ void watch_queue_clear(struct watch_queu
 	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);


Patches currently in stable-queue which might be from code@xxxxxxxx are

queue-6.1/watch_queue-prevent-dangling-pipe-pointer.patch



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