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De Francesco" Message-ID: <20220728155121.12145-1-code@siddh.me> Subject: [PATCH v3] kernel/watch_queue: Make pipe NULL while clearing watch_queue Date: Thu, 28 Jul 2022 21:21:21 +0530 X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 X-ZohoMailClient: External Cc: linux-security-modules , linux-kernel-mentees , linux-kernel , syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.com X-BeenThere: linux-kernel-mentees@lists.linuxfoundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Siddh Raman Pant via Linux-kernel-mentees Reply-To: Siddh Raman Pant Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-kernel-mentees-bounces@lists.linuxfoundation.org Sender: "Linux-kernel-mentees" 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). This causes a UAF when post_one_notification() tries to access the pipe on a key update, which is reported by syzbot. 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. Bug report: https://syzkaller.appspot.com/bug?id=1870dd7791ba05f2ea7f47f7cbdde701173973fc Reported-and-tested-by: syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.com Signed-off-by: Siddh Raman Pant --- Changes in v3: - Restore the original unlock order, and clear before unlock. - Use READ_ONCE() in post path. This was explained by David Howells in reply to v1. Not added Suggested-by since he didn't reply yet. Changes in v2: - Removed the superfluous ifdef guard. kernel/watch_queue.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index bb9962b33f95..617425e34252 100644 --- a/kernel/watch_queue.c +++ b/kernel/watch_queue.c @@ -99,7 +99,7 @@ static bool post_one_notification(struct watch_queue *wqueue, struct watch_notification *n) { void *p; - struct pipe_inode_info *pipe = wqueue->pipe; + struct pipe_inode_info *pipe = READ_ONCE(wqueue->pipe); struct pipe_buffer *buf; struct page *page; unsigned int head, tail, mask, note, offset, len; @@ -637,6 +637,12 @@ void watch_queue_clear(struct watch_queue *wqueue) spin_lock_bh(&wqueue->lock); } + /* Clearing the watch queue, so we should clean the associated pipe. */ + if (wqueue->pipe) { + wqueue->pipe->watch_queue = NULL; + wqueue->pipe = NULL; + } + spin_unlock_bh(&wqueue->lock); rcu_read_unlock(); } -- 2.35.1 _______________________________________________ Linux-kernel-mentees mailing list Linux-kernel-mentees@lists.linuxfoundation.org https://lists.linuxfoundation.org/mailman/listinfo/linux-kernel-mentees 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 999EDC04A68 for ; Thu, 28 Jul 2022 15:52:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232464AbiG1PwB (ORCPT ); Thu, 28 Jul 2022 11:52:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36248 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232435AbiG1PwB (ORCPT ); Thu, 28 Jul 2022 11:52:01 -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 819766BC35; Thu, 28 Jul 2022 08:51:58 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1659023494; cv=none; d=zohomail.in; s=zohoarc; b=Uoivu6Vw8N4PfBieS8/LwV2EQRNlD+AssZI3OJn5KE0QEVhIQfeIIvNXCVf0fWZSxTJGRTqElYNdVo5QCmsl9KKqY5H0BV6IqN3i+SIYyXbvD7fO9cKcizRRYSWAJfh2IczAHtdjCQ8d86DVa1zRPtSAZdCbFAsOubhDbPooMs4= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.in; s=zohoarc; t=1659023494; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:MIME-Version:Message-ID:Subject:To; bh=eIVJdUXeEoFT0XsTWsjdI7cmvorFUz8L2j4z7229AqY=; b=RVch7ePCikqtfxJqLaM+nv8llTUaXEANzYlKNrGZn09b2WiBWDcFingqQn1ztDMm+Qo/4Ta/LmqduVa1kCugIU+55e8oUlIeOq6W2omdIzZORaB7QLqUwWzXCBTcnWkZo+2KICsCACSJnhXZ1HPxvASKVtUYNNgJAa9F+B5wD+w= 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=1659023494; s=zmail; d=siddh.me; i=code@siddh.me; h=From:From:To:To:Cc:Cc:Message-ID:Subject:Subject:Date:Date:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=eIVJdUXeEoFT0XsTWsjdI7cmvorFUz8L2j4z7229AqY=; b=N6d4JhE7ZNMe/aFMTTJJsjLy6QJLLpWLY/QbLPU1ywmqu6AXmKXNk3+CV0gNPZhg owpUBrPVFeu9XqnZZN9JKcEn06olrfFAotIDh7BukRhSC+KlhRwrD2Motes9YjZDKor H8bneZk037DCCPqx+T1QJD7cIV0hFpj3cQIQkAGU= Received: from localhost.localdomain (43.250.165.51 [43.250.165.51]) by mx.zoho.in with SMTPS id 1659023493370468.4685004171713; Thu, 28 Jul 2022 21:21:33 +0530 (IST) From: Siddh Raman Pant To: David Howells , Christophe JAILLET , Eric Dumazet , "Fabio M. De Francesco" Cc: linux-security-modules , linux-kernel , linux-kernel-mentees , syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.com Message-ID: <20220728155121.12145-1-code@siddh.me> Subject: [PATCH v3] kernel/watch_queue: Make pipe NULL while clearing watch_queue Date: Thu, 28 Jul 2022 21:21:21 +0530 X-Mailer: git-send-email 2.35.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-ZohoMailClient: External Content-Type: text/plain; charset=utf8 Precedence: bulk List-ID: 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). This causes a UAF when post_one_notification() tries to access the pipe on a key update, which is reported by syzbot. 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. Bug report: https://syzkaller.appspot.com/bug?id=3D1870dd7791ba05f2ea7f47f7= cbdde701173973fc Reported-and-tested-by: syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.c= om Signed-off-by: Siddh Raman Pant --- Changes in v3: - Restore the original unlock order, and clear before unlock. - Use READ_ONCE() in post path. This was explained by David Howells in reply to v1. Not added Suggested-by since he didn't reply yet. Changes in v2: - Removed the superfluous ifdef guard. kernel/watch_queue.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c index bb9962b33f95..617425e34252 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; @@ -637,6 +637,12 @@ void watch_queue_clear(struct watch_queue *wqueue) =09=09spin_lock_bh(&wqueue->lock); =09} =20 +=09/* Clearing the watch queue, so we should clean the associated pipe. */ +=09if (wqueue->pipe) { +=09=09wqueue->pipe->watch_queue =3D NULL; +=09=09wqueue->pipe =3D NULL; +=09} + =09spin_unlock_bh(&wqueue->lock); =09rcu_read_unlock(); } --=20 2.35.1