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 97B7E1F55E5; Tue, 21 Jan 2025 18:11:18 +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=1737483078; cv=none; b=prRYKbT+WLoBoZBWBKbnUqIWk3h7tW0tYdMKPhFRA2xKC+D9dM1g+7GKAQRxFfP825naZtcrC3FofsFIxzttzF0zDP2dVunLmhi/8gOeM7YE2RvvYFp9kZl7hWpynliEaQOzr3iRBiO6pPWFwp581MYzNFZxB2Dhr+Zj8wDMY/0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1737483078; c=relaxed/simple; bh=AztWnKitjxvibDih7de6Iiesr38ORTwj8yIhgPKxzSw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=fu0OJn2kX2yU+1nVaLQSkCWj0tcixlcCbNlx5IQHa4CQUM2Wlhq+DVUg9lwdZALzyrgIY503+brU5MrwclaCcyf0twugm+UFAVOZ8xCBuMf3usVlk76G1rDHO+0zgqkM5uBAxngoR9WcTF20346uN8dDN2Mvaltn9Txb+w4ptT4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DGGH74eL; 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="DGGH74eL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id AD51AC4CEE0; Tue, 21 Jan 2025 18:11:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1737483078; bh=AztWnKitjxvibDih7de6Iiesr38ORTwj8yIhgPKxzSw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DGGH74eLAO/n/J/ie1S4myLRFWWr/kHYo9HD/Yg402FeRKrrUy5rAfWIm9PYFMTp+ UKwrfmvrSsNyCQt08j2KfIbi7cyMFMYb3/KKvRcXnLpKKqYFLj4n/gyqPzkGBRlTTV R5YqSnfNy2JetQqS1NVTSjR4AFa9NfJIe9jeWuW0= 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 5.15 101/127] poll_wait: add mb() to fix theoretical race between waitqueue_active() and .poll() Date: Tue, 21 Jan 2025 18:52:53 +0100 Message-ID: <20250121174533.549930266@linuxfoundation.org> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250121174529.674452028@linuxfoundation.org> References: <20250121174529.674452028@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.15-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