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 91E9D1E9B18; Thu, 30 Jan 2025 14:19:45 +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=1738246785; cv=none; b=Zxa/Utfem2hypWFQKPQcD9WcvX/WatiK1NlrVFCmS4LPXIf8JQoeThiptwbpWqOKJT7E2mYRhBRtSeeJCJ5gkjGDJOTJegDZvEkFgjaFrrsZQgxwbFUZQKIOGrXcgRVa4ba1cZIFijG7At24warLUl8kqqBsKaoiFfvY5FgnsBc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1738246785; c=relaxed/simple; bh=Ua7HeK733dA2Nh5OZxzJaZz/sqAGRXzCVO+YovMV76g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Q5Vw4wF4I42SSBluYp7mF1Cex88MhoZ5JENXORfI2H7/G1vGK2KGxNhRTnYmzucjJ8Bf4Ben8Xq52hbwj9Vu/MWCa0bBhtJ2Bbp2K/WPXwLhRlyUvsocoBYapxeAVcuR5u8Xeh+0TxGzYZomLRA9ku3itlRRj22rNQRma918Gmw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Gxe5sUSx; 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="Gxe5sUSx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1F44BC4CED2; Thu, 30 Jan 2025 14:19:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1738246785; bh=Ua7HeK733dA2Nh5OZxzJaZz/sqAGRXzCVO+YovMV76g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Gxe5sUSxS7idtfIeutK7BZwWxK2F9APkKK0DkFmG7vw8Y+Xzdx3q6aJUUuyEiEPvG qOjZQCGTs4PU55bOPeiBhJ8F1LIg/1D2aIaD9OgL1cgINjK6iQ3wGJ5WljZXOBmYkH dnemhr3LqxC8CEDMK93fiH127M98+HGGCJnuXiKc= 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 5.4 66/91] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Thu, 30 Jan 2025 15:01:25 +0100 Message-ID: <20250130140136.329604530@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250130140133.662535583@linuxfoundation.org> References: <20250130140133.662535583@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 5.4-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