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=1792597366; b=ILp0xnpj4TP3VlibpgwIXShDKKLu65VLW2KL+c+/lQMUuorOkMh+cC1g0zNVkrBEckXJ wolTTAjoH3jEvZBpEYHpVvGtHJnyh7grCQpx/EualUiDVcRBS7IvkoIQAN2UOcHanqSuJ uBPhomJmuHdiRs4YUzJ057OB/rCjiYxMs1CWOMKYs9hvT52cnwzQvpQE27MZl4lwBvFAe XieFgLZfb7rSfT93bFN+PTEBMOuzjnvC8cr5DN5S/t9WpQiGb34sQ4+3IiyA71Pyld9vc GqJ/2Ek94z4LsV2Wm/gvpvunxRAUxsffUT7uIF2xQ8RZ+IFuKwZ52WM1GtRSCOhAoUw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792597366; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=UpzJOxslNgjGEQcWy6GofmMdygicxpvnZYVwLnMByMs=; b=vlDrSJ7H91ZwLqwc76vTUqKoj/L5q0pLtKhWmxCd2I9Og3Af7EczyvtP93yXyw4Wzicn x5tDwO3UMqJ0xtxTpd8Wt1HwNsGjx7OMly1r3vomovacTp7/6oCZsrrR9jPphNznTCgY4 LtIGlz2ftqchneRsmrtzw+4fGCcwhYI0Ne4H5kSUfQmZEdVJHMCTjBJ9OCiZvtSHYvuNV NTqsbtBi9KPjdRhHWvH1sUC6QQyPWRrdQs0bCxHbHXYbK0dbvNI7tedDfg8PYNo4CpqhK 7ZMxL8fAHf6rYdAgt6JbB/vaqO1opVB8cVheblGDoWxEbFi6HpToBU+jiyU1yQ6Jtlg== 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=Q9vZfTRP; 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 DDA7B606A31D for ; Wed, 21 Oct 2026 15:42:45 +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=Q9vZfTRP Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09CA81F000C1; Wed, 21 Oct 2026 15:42:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1792597365; bh=UpzJOxslNgjGEQcWy6GofmMdygicxpvnZYVwLnMByMs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Q9vZfTRPqBgcyNd3EetE3ZmCO3q/NiP8vQRS6V252e8PFApgR2Q7BrDWtVLrRtikc W+95pAGDonjBj95GfVbkgisa5c0fSQQieuWuf5eg16GkdtSYSEXFdJzyzjD7rTVnWe dT76GQoryU3koh1KOyGXC0bzpxnjxUdhJfNGy2SPY7lrInKBpye5pgGrTh1DVy7h+e Bt8u0ONrToTQCEZtStrwd+bLkAvcxPd+HdzTDCt1kZGljAXXs+kLXRREcao7u7DeKP 9CP22SVAUuWiSRAhANWAf/VP4mWbbwn6ii6t19dLe8RiAZBzWHT5L6NogO3R3gjMAK LiUIv7HnMFuYQ== 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 6.6.y 2/2] watch_queue: Fix note pool publication race in watch_queue_set_size() Date: Wed, 21 Oct 2026 11:42:43 -0400 Message-ID: <20261021154232.364295-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261021154232.364295-1-sashal@kernel.org> References: <2026102121-dial-citric-080a@gregkh> <20261021154232.364295-1-sashal@kernel.org> 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) 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 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