From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 308343B0AE4; Thu, 8 Oct 2026 22:42:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791499378; cv=none; b=X+0zDe7Dgn4ltbny6GSGxD3ndzQRl1RREfhOOOCh7JHr+wXU5BV8T6Um7G8S8X6O0w3sOZMCYH0M0JeLu3DpkkWTbXUe5mTDlwoXAAakml43biMvhgLZBEGOLYEpgQHCPiDX5mFo3+oB62fRivR7il3pfKIFPD5o+l5txjssKcw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791499378; c=relaxed/simple; bh=+goYj/o+YwHUjbxMWjYtF5BIR5nU+fqhQjD3RDm4t/c=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=GM/zg9Z2H519EYo9ODxr4XNrimrhd+9iiW7O20+6AX8vg33fR99pSaykQCGGo3f9cnZd7IJAjZ77+GQUrAdUZNBk4bV45igoCabvF0BRDz35+xO6OmTGPWldcLeDBKuvYDXeEAx0L203fHhjGz9K8iTJ4gXSUp2FVLyBK1ziWaw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=gZo/HnFl; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="gZo/HnFl" Received: from mac.lan (unknown [52.172.102.222]) by linux.microsoft.com (Postfix) with ESMTPSA id AC43020B7166; Thu, 8 Oct 2026 15:41:53 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com AC43020B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1791499319; bh=OP5F7DlztNufb0JidK9WhyBFcBtyfMxwleYWMwnNSFs=; h=From:To:Cc:Subject:Date:From; b=gZo/HnFlMOWyYrAzIdQxtcKR3swk5/tAoxih5V4Bx0E7wL9S5k2xm4NrZe7F+mR7w zTvRj7pV/1XKhs6GvG7U8IBGz5f+PNo9Kc5/I4eVVI1jIoaY93cdLl3H5xT7WcsoiP RzGyVfDK5V1eCGvjqBbG/ByB0dgWWwmt167pW78k= From: "Cen Zhang (Microsoft)" To: David Howells Cc: Christian Brauner , Davidlohr Bueso , Kees Cook , "Dae R . Jeong" , linux-kernel@vger.kernel.org, stable@vger.kernel.org, AutonomousCodeSecurity@microsoft.com, tgopinath@linux.microsoft.com, Cen Zhang Subject: [PATCH] watch_queue: Fix missing locking in watch_queue_set_size() Date: Thu, 8 Oct 2026 18:42:33 -0400 Message-ID: <20261008224233.9675-1-cenzhang@linux.microsoft.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 does not take wqueue->lock, so the four stores are not atomic as a group and, 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 putting the four publication stores under wqueue->lock. post_one_notification() already runs with that lock held, so a poster now sees either the whole pool or none of it. 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 Assisted-by: LLM Signed-off-by: Cen Zhang (Microsoft) --- kernel/watch_queue.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index 538520861e8b..9fb3035b3ebd 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -294,10 +294,13 @@ long watch_queue_set_size(struct pipe_inode_info *pipe, unsigned int nr_notes) goto error_p; bitmap_fill(bitmap, nr_notes); + /* Use lock since watches may already be attached. */ + spin_lock_bh(&wqueue->lock); wqueue->notes = pages; wqueue->notes_bitmap = bitmap; wqueue->nr_pages = nr_pages; wqueue->nr_notes = nr_notes; + spin_unlock_bh(&wqueue->lock); return 0; error_p: -- 2.55.0