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 3C9EC225403; Mon, 13 Jan 2025 18:36:46 +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=1736793406; cv=none; b=jtjw4CWAbW9VwbxvpLLvaZkmZmnKJUgKwhC23ApTVX6xj8b+lZC3zofJ8CotFNPO8j9uuTz6qxh5ATS1hh7S9jXk5jc4BX/WmAO12tayp7ltptBeXvjbB6kX1Qd+jSLTCZY2XfsejYNi9z5cJ6JtR7QfQWF5angjb4H7HdtiYMs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1736793406; c=relaxed/simple; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=prt3Pt6Re6rMwPvmEKY1KimLTCt3vOifad1cHBkPW2/Cn6zW7L4I2rtP6BBH5xFxk8mND6c0b5CEWMBEumRao/RtktSotAI1DN1ZmOYT0qpHWR2F0jn4Znn3j4swD23cWV2JxcL4SkwkBoqDuM5SxetkRloZQw22TYE96RDtZkU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=a7chWYPz; 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="a7chWYPz" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 3A831C4CEE1; Mon, 13 Jan 2025 18:36:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1736793406; bh=HbtvBeIcZy2P32mTLCcMuGA1L+t+DPjp5Ry6smyZ6KQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=a7chWYPzF1c4tBrE0gMDL2S5pT5mmoyE4nBrI41i9xGCqrDRudwuweBLWLjGM3M4x PhcKVkriJfkdBWJhvJy1Yv4G9mm+VPMBcaSlZz93ubFAoQPh1DMSIdtnlu+HsbrlJY YKATGi37r5kDfTj608xVBw19JlYm25rQBsSrVaQDyIqdid1p3HGX02Ba+ryXRXlEid 8+umLm3BSf93/DX05A3IR8BT2rC5f4kg8zal0fdupWM8tcrDx4sbA5gA7Y9MGeaxaX xh+tccEF/M/PfK+rv1BXciwVUs6k0MpJXIda9ag3NF4JX3xZZdgN2QGnLbriPgGm+k s6SlPkuP3RKBQ== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Oleg Nesterov , Christian Brauner , Sasha Levin , kees@kernel.org, arnd@arndb.de, ak@linux.intel.com Subject: [PATCH AUTOSEL 5.4 4/4] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Mon, 13 Jan 2025 13:36:33 -0500 Message-Id: <20250113183633.1784590-4-sashal@kernel.org> X-Mailer: git-send-email 2.39.5 In-Reply-To: <20250113183633.1784590-1-sashal@kernel.org> References: <20250113183633.1784590-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 5.4.289 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