From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id D92BF1E6DCF; Thu, 30 Jan 2025 14:25:21 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738247121; cv=none; b=l86yR1xJZKBUMXZnkXBXU1bkZG9c6uAim5jvdkWH9uWOziVBelDw/Lfr3vhJ9Wnk0Z8VwEeDdj66sT7O+XKUVZ+4xqV8wl4wjoTXIXDuW9r2xbmfjIszTM4+zinXVPw/0OC8DVfOYL6S4vmi4sBwAfHpK0D2b9OlQ1f1Pp5wvhE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738247121; c=relaxed/simple; bh=CDmMfYJKusMkHZHzsc5wFa3WvCIzoA7m7IsG2LMls4Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dFZfMT53Mo823cnY21TW7xWEUltGebv8o7+c916E5S56ccXBA8fghJJGM8RnaNl+yt3R+xD9mDxRt7jnu4lyDX5AjZNzXK5ag2mP8tt6rHR7tV+xiznCscqp2eXYDsFzrVDRZPyiR/T/O3VshIbOnogpieu4wxQ5aDWw70xrC2A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=BjGutgr2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="BjGutgr2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6121EC4CEE2; Thu, 30 Jan 2025 14:25:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1738247121; bh=CDmMfYJKusMkHZHzsc5wFa3WvCIzoA7m7IsG2LMls4Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=BjGutgr2XL19GTHz9jt8AcZda7gh/Wz8npoBK0m5aCDFXK9IHqPuX4GcMQyYvO2kc BO45UP2zmeQX+xo4dPPqAqUA0YnH76T5vCuc/8Upub6E+2HUuANF417tHuVMBFcx59 FdOw8LMR5vJ6AsRxokcKASHOb5kBFU1eMCe/mhdY= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Oleg Nesterov , Christian Brauner , Sasha Levin Subject: [PATCH 5.10 089/133] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Thu, 30 Jan 2025 15:01:18 +0100 Message-ID: <20250130140146.103141268@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250130140142.491490528@linuxfoundation.org> References: <20250130140142.491490528@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Oleg Nesterov [ Upstream commit cacd9ae4bf801ff4125d8961bb9a3ba955e51680 ] As the comment above waitqueue_active() explains, it can only be used if both waker and waiter have mb()'s that pair with each other. However __pollwait() is broken in this respect. This is not pipe-specific, but let's look at pipe_poll() for example: poll_wait(...); // -> __pollwait() -> add_wait_queue() LOAD(pipe->head); LOAD(pipe->head); In theory these LOAD()'s can leak into the critical section inside add_wait_queue() and can happen before list_add(entry, wq_head), in this case pipe_poll() can race with wakeup_pipe_readers/writers which do smp_mb(); if (waitqueue_active(wq_head)) wake_up_interruptible(wq_head); There are more __pollwait()-like functions (grep init_poll_funcptr), and it seems that at least ep_ptable_queue_proc() has the same problem, so the patch adds smp_mb() into poll_wait(). Link: https://lore.kernel.org/all/20250102163320.GA17691@redhat.com/ Signed-off-by: Oleg Nesterov Link: https://lore.kernel.org/r/20250107162717.GA18922@redhat.com Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- include/linux/poll.h | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/include/linux/poll.h b/include/linux/poll.h index 7e0fdcf905d2e..a4af5e14dffed 100644 --- a/include/linux/poll.h +++ b/include/linux/poll.h @@ -43,8 +43,16 @@ typedef struct poll_table_struct { static inline void poll_wait(struct file * filp, wait_queue_head_t * wait_address, poll_table *p) { - if (p && p->_qproc && wait_address) + if (p && p->_qproc && wait_address) { p->_qproc(filp, wait_address, p); + /* + * This memory barrier is paired in the wq_has_sleeper(). + * See the comment above prepare_to_wait(), we need to + * ensure that subsequent tests in this thread can't be + * reordered with __add_wait_queue() in _qproc() paths. + */ + smp_mb(); + } } /* -- 2.39.5