From mboxrd@z Thu Jan 1 00:00:00 1970 From: PanBian Subject: Re: [PATCH] f2fs: read page index before freeing Date: Mon, 26 Nov 2018 18:28:41 +0800 Message-ID: <20181126102841.GA94853@bp> References: <1542884326-74903-1-git-send-email-bianpan2016@163.com> <3ebe6814-586e-77e8-52fa-47fb61d760f5@huawei.com> Reply-To: PanBian Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from [172.30.20.202] (helo=mx.sourceforge.net) by sfs-ml-4.v29.lw.sourceforge.com with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.90_1) (envelope-from ) id 1gRE8f-0006Wp-QO for linux-f2fs-devel@lists.sourceforge.net; Mon, 26 Nov 2018 10:29:13 +0000 Received: from m12-15.163.com ([220.181.12.15]) by sfi-mx-3.v28.lw.sourceforge.com with esmtp (Exim 4.90_1) id 1gRE8L-0041Xr-Bv for linux-f2fs-devel@lists.sourceforge.net; Mon, 26 Nov 2018 10:29:13 +0000 Content-Disposition: inline In-Reply-To: <3ebe6814-586e-77e8-52fa-47fb61d760f5@huawei.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net To: Chao Yu Cc: Jaegeuk Kim , linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net On Mon, Nov 26, 2018 at 05:13:53PM +0800, Chao Yu wrote: > Hi Pan, > > On 2018/11/22 18:58, Pan Bian wrote: > > The function truncate_node frees the page with f2fs_put_page. However, > > the page index is read after that. So, the patch reads the index before > > freeing the page. > > I notice that you found another use-after-free bug in ext4, out of > curiosity, I'd like to ask how do you find those bugs? by tool or code review? I found such bugs by the aid of a tool I wrote recently. I designed a method to automatically find paired alloc/free functions. With such functions, I wrote two checkers, one to check mismatched alloc/free bugs, the other to check use-after-free and double-free bugs. Best regards, Pan Bian