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 0FB45C00140 for ; Wed, 3 Aug 2022 01:08:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231392AbiHCBIm (ORCPT ); Tue, 2 Aug 2022 21:08:42 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35032 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229648AbiHCBIm (ORCPT ); Tue, 2 Aug 2022 21:08:42 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id F12EF5509E; Tue, 2 Aug 2022 18:08:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 93BABB82029; Wed, 3 Aug 2022 01:08:39 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 200F8C433D6; Wed, 3 Aug 2022 01:08:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1659488918; bh=nFvBbjR87hTY904i1+8Fy8FiC4hebZxTVV+qEYLIg/w=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IK44tNyATmuHIJbWXYRZMj56Cu8AdGwvjirxqR90PmsqSdmS1JoZOnmyd7NUcUKWl avx17DBgigH9IH3d1beVf0Z7h0wMJxGe8DW3jjidN0HKn5sxI9w9X2I/c3qDMlmVKj kUjPBQMDanzoZX1U6MsM3KUxl80kDuh9qN6OloReq/EVXf4soGAWlONt8wd2aA03zo /DffC6Xko1Qxt42aK2yLSp9t+oSsimdWBspR6JY7viQKAXYc95G3u1jxM/t0rexV67 fUvT76BqSpCP7BHZQyZ1K4WH+US2HghnrlSlxP3jk7TrDzhp2tzJ/RaBD17N/7uYRn EQ9yTuwrgkh8Q== Date: Tue, 2 Aug 2022 18:08:36 -0700 From: Eric Biggers To: Siddh Raman Pant Cc: David Howells , Christophe JAILLET , Eric Dumazet , "Fabio M. De Francesco" , linux-security-modules , linux-kernel , linux-kernel-mentees , syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.com Subject: Re: [PATCH v3] kernel/watch_queue: Make pipe NULL while clearing watch_queue Message-ID: References: <20220728155121.12145-1-code@siddh.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220728155121.12145-1-code@siddh.me> Precedence: bulk List-ID: On Thu, Jul 28, 2022 at 09:21:21PM +0530, Siddh Raman Pant wrote: > 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. Didn't this already get fixed by the following commit? commit 353f7988dd8413c47718f7ca79c030b6fb62cfe5 Author: Linus Torvalds Date: Tue Jul 19 11:09:01 2022 -0700 watchqueue: make sure to serialize 'wqueue->defunct' properly With that, post_one_notification() only runs while the watch_queue is locked and not "defunct". So it's guaranteed that the pipe still exists. Any concurrent free_pipe_info() waits for the watch_queue to be unlocked in watch_queue_clear() before proceeding to free the pipe. So where is there still a bug? > > Bug report: https://syzkaller.appspot.com/bug?id=1870dd7791ba05f2ea7f47f7cbdde701173973fc > Reported-and-tested-by: syzbot+c70d87ac1d001f29a058@syzkaller.appspotmail.com If this actually does fix something, then it's mixing Fixes and Cc stable tags. > 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(); > } And this is clearly the wrong fix anyway, since it makes the call to put_watch_queue() in free_pipe_info() never be executed. So AFAICT, this patch introduces a memory leak, and doesn't actually fix anything... - Eric