FAILED: patch "[PATCH] watch_queue: Fix note pool publication race in" failed to apply to 6.6-stable tree

FAILED: patch "[PATCH] watch_queue: Fix note pool publication race in" failed to apply to 6.6-stable tree

[gregkh]

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 5e531d62f1f8834faf7a4eed0d41105cf6570a8f
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2026102121-dial-citric-080a@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:



thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5e531d62f1f8834faf7a4eed0d41105cf6570a8f Mon Sep 17 00:00:00 2001
From: "Cen Zhang (Microsoft)" <cenzhang@linux.microsoft.com>
Date: Fri, 9 Oct 2026 18:47:15 -0400
Subject: [PATCH] watch_queue: Fix note pool publication race in
 watch_queue_set_size()

There is a race between watch_queue_set_size() and post_one_notification().
watch_queue_set_size() publishes wqueue->notes, notes_bitmap, nr_pages and
nr_notes with plain stores, and post_one_notification() reads them with
plain loads under a different lock, so nothing orders the four stores
against the poster's loads: depending on the build, notes can be stored
last (gcc 14 on x86-64 does this).  Since keyctl_watch_key() lets a watch
attach to a queue before it is sized, post_one_notification() can already
be running on another CPU at that moment: it reads nr_notes > 0, passes
its bounds check, and then reads notes while it is still NULL,
dereferencing notes[0].

An unprivileged user triggers this reliably by watching one of its own
keys through a notification pipe and racing ioctl(IOC_WATCH_QUEUE_SET_SIZE)
on that pipe against keyctl(KEYCTL_SETPERM) on the key from another CPU,
triggering:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:post_one_notification.isra.0+0xa2/0x1e0
  Call Trace:
   __post_watch_notification+0x148/0x180
   keyctl_setperm_key+0x119/0x130
   do_syscall_64+0x108/0x4c0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Kernel panic - not syncing: Fatal exception in interrupt

Fix this by publishing nr_notes last with smp_store_release(), and by
reading it once with smp_load_acquire() in post_one_notification() before
the bitmap and the page array are touched.  A poster that observes a
non-zero nr_notes then also observes the pool behind it; one that observes
zero drops the notification as before.

Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Reported-by: Dae R. Jeong <threeearcat@gmail.com>
Closes: https://lore.kernel.org/all/ZT-S8Q7tyutcvu_q@dragonet/
Reported-by: AutonomousCodeSecurity@microsoft.com
Suggested-by: Dae R. Jeong <threeearcat@gmail.com>
Signed-off-by: Cen Zhang (Microsoft) <cenzhang@linux.microsoft.com>
Link: https://patch.msgid.link/20261009224715.46121-1-cenzhang@linux.microsoft.com
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 538520861e8b..932a88ac1f39 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -101,7 +101,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	struct pipe_inode_info *pipe = wqueue->pipe;
 	struct pipe_buffer *buf;
 	struct page *page;
-	unsigned int head, tail, note, offset, len;
+	unsigned int head, tail, note, offset, len, nr_notes;
 	bool done = false;
 
 	spin_lock_irq(&pipe->rd_wait.lock);
@@ -111,8 +111,10 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	if (pipe_full(head, tail, pipe->ring_size))
 		goto lost;
 
-	note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
-	if (note >= wqueue->nr_notes)
+	/* Pairs with the smp_store_release() in watch_queue_set_size(). */
+	nr_notes = smp_load_acquire(&wqueue->nr_notes);
+	note = find_first_bit(wqueue->notes_bitmap, nr_notes);
+	if (note >= nr_notes)
 		goto lost;
 
 	page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
@@ -297,7 +299,8 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
 	wqueue->notes = pages;
 	wqueue->notes_bitmap = bitmap;
 	wqueue->nr_pages = nr_pages;
-	wqueue->nr_notes = nr_notes;
+	/* Pairs with the smp_load_acquire() in post_one_notification(). */
+	smp_store_release(&wqueue->nr_notes, nr_notes);
 	return 0;
 
 error_p:

[PATCH 6.6.y 1/2] kernel/watch_queue: Use pipe_buf() to retrieve the pipe buffer

[Sasha Levin]

From: K Prateek Nayak <kprateek.nayak@amd.com>

[ Upstream commit 547476063e123e73fc3aea8432104ab092ffea84 ]

Use pipe_buf() helper to retrieve the pipe buffer in
post_one_notification() replacing the open-coded the logic.

Suggested-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Link: https://lore.kernel.org/r/20250307052919.34542-3-kprateek.nayak@amd.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: 5e531d62f1f8 ("watch_queue: Fix note pool publication race in watch_queue_set_size()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/watch_queue.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 17254597accd4..0840603c91e37 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -101,12 +101,11 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	struct pipe_inode_info *pipe = wqueue->pipe;
 	struct pipe_buffer *buf;
 	struct page *page;
-	unsigned int head, tail, mask, note, offset, len;
+	unsigned int head, tail, note, offset, len;
 	bool done = false;
 
 	spin_lock_irq(&pipe->rd_wait.lock);
 
-	mask = pipe->ring_size - 1;
 	head = pipe->head;
 	tail = pipe->tail;
 	if (pipe_full(head, tail, pipe->ring_size))
@@ -124,7 +123,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	memcpy(p + offset, n, len);
 	kunmap_atomic(p);
 
-	buf = &pipe->bufs[head & mask];
+	buf = pipe_buf(pipe, head);
 	buf->page = page;
 	buf->private = (unsigned long)wqueue;
 	buf->ops = &watch_queue_pipe_buf_ops;
@@ -147,7 +146,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	return done;
 
 lost:
-	buf = &pipe->bufs[(head - 1) & mask];
+	buf = pipe_buf(pipe, head - 1);
 	buf->flags |= PIPE_BUF_FLAG_LOSS;
 	goto out;
 }
-- 
2.53.0

[PATCH 6.6.y 2/2] watch_queue: Fix note pool publication race in watch_queue_set_size()

[Sasha Levin]

From: "Cen Zhang (Microsoft)" <cenzhang@linux.microsoft.com>

[ Upstream commit 5e531d62f1f8834faf7a4eed0d41105cf6570a8f ]

There is a race between watch_queue_set_size() and post_one_notification().
watch_queue_set_size() publishes wqueue->notes, notes_bitmap, nr_pages and
nr_notes with plain stores, and post_one_notification() reads them with
plain loads under a different lock, so nothing orders the four stores
against the poster's loads: depending on the build, notes can be stored
last (gcc 14 on x86-64 does this).  Since keyctl_watch_key() lets a watch
attach to a queue before it is sized, post_one_notification() can already
be running on another CPU at that moment: it reads nr_notes > 0, passes
its bounds check, and then reads notes while it is still NULL,
dereferencing notes[0].

An unprivileged user triggers this reliably by watching one of its own
keys through a notification pipe and racing ioctl(IOC_WATCH_QUEUE_SET_SIZE)
on that pipe against keyctl(KEYCTL_SETPERM) on the key from another CPU,
triggering:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:post_one_notification.isra.0+0xa2/0x1e0
  Call Trace:
   __post_watch_notification+0x148/0x180
   keyctl_setperm_key+0x119/0x130
   do_syscall_64+0x108/0x4c0
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
  Kernel panic - not syncing: Fatal exception in interrupt

Fix this by publishing nr_notes last with smp_store_release(), and by
reading it once with smp_load_acquire() in post_one_notification() before
the bitmap and the page array are touched.  A poster that observes a
non-zero nr_notes then also observes the pool behind it; one that observes
zero drops the notification as before.

Fixes: c73be61cede5 ("pipe: Add general notification queue support")
Reported-by: Dae R. Jeong <threeearcat@gmail.com>
Closes: https://lore.kernel.org/all/ZT-S8Q7tyutcvu_q@dragonet/
Reported-by: AutonomousCodeSecurity@microsoft.com
Suggested-by: Dae R. Jeong <threeearcat@gmail.com>
Signed-off-by: Cen Zhang (Microsoft) <cenzhang@linux.microsoft.com>
Link: https://patch.msgid.link/20261009224715.46121-1-cenzhang@linux.microsoft.com
Reviewed-by: Bradley Morgan <brads@mainlining.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/watch_queue.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index 0840603c91e37..d5a76a5efd204 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -101,7 +101,7 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	struct pipe_inode_info *pipe = wqueue->pipe;
 	struct pipe_buffer *buf;
 	struct page *page;
-	unsigned int head, tail, note, offset, len;
+	unsigned int head, tail, note, offset, len, nr_notes;
 	bool done = false;
 
 	spin_lock_irq(&pipe->rd_wait.lock);
@@ -111,8 +111,10 @@ static bool post_one_notification(struct watch_queue *wqueue,
 	if (pipe_full(head, tail, pipe->ring_size))
 		goto lost;
 
-	note = find_first_bit(wqueue->notes_bitmap, wqueue->nr_notes);
-	if (note >= wqueue->nr_notes)
+	/* Pairs with the smp_store_release() in watch_queue_set_size(). */
+	nr_notes = smp_load_acquire(&wqueue->nr_notes);
+	note = find_first_bit(wqueue->notes_bitmap, nr_notes);
+	if (note >= nr_notes)
 		goto lost;
 
 	page = wqueue->notes[note / WATCH_QUEUE_NOTES_PER_PAGE];
@@ -297,7 +299,8 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes)
 	wqueue->notes = pages;
 	wqueue->notes_bitmap = bitmap;
 	wqueue->nr_pages = nr_pages;
-	wqueue->nr_notes = nr_notes;
+	/* Pairs with the smp_load_acquire() in post_one_notification(). */
+	smp_store_release(&wqueue->nr_notes, nr_notes);
 	return 0;
 
 error_p:
-- 
2.53.0