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 0602C21D5A4; Mon, 13 Jan 2025 18:36:19 +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=1736793379; cv=none; b=LNRV7BPDTsg69wyDMMyZ0WD5oUEGCaDLcRTURgMmWizyafhr94abC1oauC9Bj7HDNLjDs9DTq/mNrPZTmGG+B9pX+DGR/IozU7iKyJW5F8K9pzDUpAk4j2fnmXqTbS5zpolSHQBjwx4W6dhMNumxvrhIpJUcAEjU7f27ukaVYJU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736793379; c=relaxed/simple; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=oY3B6ReqZwc8b9tps0/Vbsi/CQBe3b6DMQStK73eyrLFGkrCr7qeuNEAaV8sXmM0SFCixJp5/i4f1B5DyIInDGX/7kXffyTTQZQxBmcuQBHDIwqfk30+PnQTrP3pM6lr6k5cLHYShK+NClpkFP9gpgLq3SKGaP1Qt7NGUZWKPoA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CjHQprCl; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="CjHQprCl" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E2FC0C4CED6; Mon, 13 Jan 2025 18:36:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736793378; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=CjHQprClDk3P2QobjgP0cQnm7/JcfkmyEw2KG3R1DspEADOtLHqPhBiMOvhBqJm2G nT16WhRBgai2WTAbEjkcm8hW2NrLMbdjxIF9XvkdSFwFfFtVzxzpQnl7LRGDmTssWp QY58XttXPQu3D2RXZSJr5uhEbiWaA0HPCUXL8jmXPNu1giiG9lB3swepM5GpI1D00U G5QOpOucQdCwgW6ICQT4Jm+FLCPx4E5qXwOo4tI+F4uqgFhQ08Ek7lJcxU/RKFlKBv GlwHygxTwxBg5z6dTStessgho4/jQdKawP31ILtKVwCPykxkqa0MF6jffCmCKdbvmN GZPWv1yAKkl7g== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Christian Brauner , Sasha Levin , ak@linux.intel.com, jack@suse.cz, kees@kernel.org, arnd@arndb.de Subject: [PATCH AUTOSEL 5.15 6/6] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Mon, 13 Jan 2025 13:36:00 -0500 Message-Id: <20250113183601.1784402-6-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250113183601.1784402-1-sashal@kernel.org> References: <20250113183601.1784402-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.15.176 Content-Transfer-Encoding: 8bit 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 7e0fdcf905d2..a4af5e14dffe 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