From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792632620; b=wLdTe1ohfNHA3JGbuh+h+D9VJb10c2cmajg/e6KsJ2Y9g9RnMTTDC0BHEZHwxUF4PFLW ab8ktkSjt5FeHMCTQfH7jsoTJFR2TBhdTC0hnDDQPzLGq0Klr79OYiL0rRrbZ35zkLkjf RsnhNjSBjLk0f8s6CUVrEZ0FfhhO1iLm6EcvkZi7MHxaRhKMM8htc1SvIVRiwxegeRgfB z0v/aXePWYX+rkg+9D9WTQbo7funhx+XLmzU72sbj8/je+3eITLlqoZdM5llFgThV6+4z V76F9shE5+xvFtAAOCidDKeZ0FKirNOLhb8cEYqXwFf4kjCSYCSsQXV+02B2hdDVcLw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792632620; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=qUl6azi9Ik7qw0j4SQxhd0AHDbHkqRW9GcyQMAwPs5k=; b=X6KHxV2tnng+F/BbVU2JCTKEVBxd5kxYS+efEd4Cp4967mCBxuepg+pD/tgcWknkJgUd fc4d82Npi7ltFHMKxuF8kAnLWpTQvvIaEenHJ7GeeoxDtyMsh83AFur9GSYoYr/kP+EJS fdJu+iHzPG0mVLWequtR8Eeo8/rKTks+lbP90orgMLpC+zsDVpp/sbhlI0s6lkeGSEsiG 4fuS7CS1xdaAh6ppbTZvMBMoUR3GyQFmMu9PRuXm0cI/E9L5/zeToFvxk/U4nEn8qeFSz GiS5nRXGJ0cSWXelYLfBQtXst4xUszsvkquAIAb+7D2tkW7AjIMhdi/2emzY8/Bk2nA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PXDhNqtG; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 095CC606A319 for ; Thu, 22 Oct 2026 01:30:19 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=PXDhNqtG Received: by smtp.kernel.org (Postfix) with ESMTPSA id DB0FE1F000C1; Thu, 22 Oct 2026 01:30:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792632619; bh=qUl6azi9Ik7qw0j4SQxhd0AHDbHkqRW9GcyQMAwPs5k=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=PXDhNqtGXkS0k9nPlVtYwtD77v90AU1XcpxF0IgrQENN1V8g7mCAeI6t/EjIOrHgs /UhChP24tPaxYfLl8J9rvzI2lhW+LV+noQDBRw4Fk3QZ0rTq2HL8Pgahyfta1HcjES 9RcbTF71NJR2AAo9MxjlmfpbgtpE+nHQ+8knfFYRaIGJMUphAKs3cB7wGzlQQSHet0 pDr9WWgmyZEUEILDosN1rGCbmTnDmfZx4ZeLdLqPnKP4TJ5aeiRxlE8w5qRqh4/7zi 9s/4SCJswIJ1Vood0eA7PUlQBqLKE3nB3rTzN9wox3xTY6temLrN9JgotWdjm3wwdg 8N14bexxYBy7A== From: Sasha Levin To: stable@vger.kernel.org Cc: "Cen Zhang (Microsoft)" , "Dae R. Jeong" , AutonomousCodeSecurity@microsoft.com, Bradley Morgan , "Christian Brauner (Amutable)" , Sasha Levin Subject: [PATCH 5.15.y] watch_queue: Fix note pool publication race in watch_queue_set_size() Date: Wed, 21 Oct 2026 21:30:17 -0400 Message-ID: <20261022012949.694106-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026102125-proud-dial-e6e3@gregkh> References: <2026102125-proud-dial-e6e3@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "Cen Zhang (Microsoft)" [ 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 Closes: https://lore.kernel.org/all/ZT-S8Q7tyutcvu_q@dragonet/ Reported-by: AutonomousCodeSecurity@microsoft.com Suggested-by: Dae R. Jeong Signed-off-by: Cen Zhang (Microsoft) Link: https://patch.msgid.link/20261009224715.46121-1-cenzhang@linux.microsoft.com Reviewed-by: Bradley Morgan Cc: Signed-off-by: Christian Brauner (Amutable) [ sashal: adjusted post_one_notification() context for the existing mask variable and null-pipe check ] Signed-off-by: Sasha Levin --- 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 6ed37bc95cb7b..b14dbef344996 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -102,7 +102,7 @@ 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, mask, note, offset, len; + unsigned int head, tail, mask, note, offset, len, nr_notes; bool done = false; if (!pipe) @@ -116,8 +116,10 @@ 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]; @@ -305,7 +307,8 @@ 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