From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9C8C0C19F2A for ; Thu, 4 Aug 2022 13:32:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239877AbiHDNcS (ORCPT ); Thu, 4 Aug 2022 09:32:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36774 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239815AbiHDNcE (ORCPT ); Thu, 4 Aug 2022 09:32:04 -0400 Received: from sender-of-o53.zoho.in (sender-of-o53.zoho.in [103.117.158.53]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 32B223D597 for ; Thu, 4 Aug 2022 06:31:51 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1659619869; cv=none; d=zohomail.in; s=zohoarc; b=BuDznUG+XJjgZb6WOz1pkcQ7d1CiQCJ/Rl0Fxs92y5cQAUjXUHkSsOgA4qUBlagjlEwSaJgvM1XrfFP0/bPx+4gZLW7LH3k04lf2UsJ5ehlksME/y+esyGGVnvzL96eCjCZIhERXY6wx/zceqHkH5jmdgtMxCMpPjozI2BcVuDQ= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.in; s=zohoarc; t=1659619869; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:To; bh=y1Ovbial2FYc1BrqdnC91HLquYb0VtXHNQSWJNxyGjk=; b=Vt65eUbIR6LC/lPVxeJx2K/5XfUprgeWduCXOQzfPRMSLHVOwoXQqGtThc/ZBwZkUIao4x/pMRrWYV0fueCEmTt9pkxcDfhneYni5CPYO846NCXyGOGyv2jyGBOrEpN+cSkwSXGRVPBYy5QppY/QJy8ozquJzJyWj/orNv4eiqw= ARC-Authentication-Results: i=1; mx.zohomail.in; dkim=pass header.i=siddh.me; spf=pass smtp.mailfrom=code@siddh.me; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1659619869; s=zmail; d=siddh.me; i=code@siddh.me; h=From:From:To:To:Cc:Cc:Message-ID:Subject:Subject:Date:Date:In-Reply-To:References:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=y1Ovbial2FYc1BrqdnC91HLquYb0VtXHNQSWJNxyGjk=; b=BmE3ziSSl6JohUDLEyLx9hkQtNrVtt4pVMlwGVL5T7lxvJM9+qulfAiFSYYw0yzI 3fwxlkcUnIXTr/0ZKSxEOH6JZi3QBqN3ksPmBM9Liq7TadXR7ZpSQ7C+gLKYvTj5k/O QCewWX5y3RaccVFA598ES41lNj82qLKWXAv528ZQ= Received: from localhost.localdomain (103.250.137.206 [103.250.137.206]) by mx.zoho.in with SMTPS id 1659619867360682.4482276982302; Thu, 4 Aug 2022 19:01:07 +0530 (IST) From: Siddh Raman Pant To: Eric Biggers , Jonathan Corbet , David Howells , Randy Dunlap , Mauro Carvalho Chehab , Christophe JAILLET , Eric Dumazet Cc: linux-kernel , linux-kernel-mentees Message-ID: Subject: [PATCH 1/3 v4] kernel/watch_queue: Remove dangling pipe reference while clearing watch_queue Date: Thu, 4 Aug 2022 19:00:22 +0530 X-Mailer: git-send-email 2.35.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Content-Type: text/plain; charset=utf8 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If not done, a reference to a freed pipe remains in the watch_queue, as this function is called before freeing a pipe in free_pipe_info() (see line 834 of fs/pipe.c). We also need to use READ_ONCE() in post_one_notification() to prevent the compiler from optimising and loading a non-NULL value from wqueue->pipe. Signed-off-by: Siddh Raman Pant --- Changes in v4: - Brought the lines towards the start rather than the end. - Removed incorrect NULLing of wqueue->pipe->watch_queue. The latter was pointed out by Eric Biggers in reply to v3. Changes in v3: - Restored the original unlock order, and clear before unlock. - Used READ_ONCE() in post path. This was explained by David Howells in reply to v1. Changes in v2: - Removed the superfluous ifdef guard. kernel/watch_queue.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index a6f9bdd956c3..8999c4e3076d 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -99,7 +99,7 @@ static bool post_one_notification(struct watch_queue *wqu= eue, =09=09=09=09 struct watch_notification *n) { =09void *p; -=09struct pipe_inode_info *pipe =3D wqueue->pipe; +=09struct pipe_inode_info *pipe =3D READ_ONCE(wqueue->pipe); =09struct pipe_buffer *buf; =09struct page *page; =09unsigned int head, tail, mask, note, offset, len; @@ -606,6 +606,9 @@ void watch_queue_clear(struct watch_queue *wqueue) =09/* Prevent new notifications from being stored. */ =09wqueue->defunct =3D true; =20 +=09/* This pipe will get freed by caller, and we are anyways clearing. */ +=09wqueue->pipe =3D NULL; + =09while (!hlist_empty(&wqueue->watches)) { =09=09watch =3D hlist_entry(wqueue->watches.first, struct watch, queue_nod= e); =09=09hlist_del_init_rcu(&watch->queue_node); --=20 2.35.1