From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752570AbdBPBZo (ORCPT ); Wed, 15 Feb 2017 20:25:44 -0500 Received: from szxga02-in.huawei.com ([119.145.14.65]:59965 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751184AbdBPBZm (ORCPT ); Wed, 15 Feb 2017 20:25:42 -0500 Subject: Re: [PATCH 3.16 105/306] vfs,mm: fix a dead loop in truncate_inode_pages_range() To: Ben Hutchings , , References: CC: , Linus Torvalds , Christoph Hellwig , "Al Viro" , Dave Chinner From: Wei Fang Message-ID: <58A4FF81.4090208@huawei.com> Date: Thu, 16 Feb 2017 09:25:21 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.236.214] X-CFilter-Loop: Reflected X-Mirapoint-Virus-RAPID-Raw: score=unknown(0), refid=str=0001.0A020205.58A4FF8F.0198,ss=1,re=0.000,recu=0.000,reip=0.000,cl=1,cld=1,fgs=0, ip=0.0.0.0, so=2013-06-18 04:22:30, dmn=2013-03-21 17:37:32 X-Mirapoint-Loop-Id: 9cb7a56cf6e3d82f9de89ddebf180b08 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Ben, Commit d05c5f7ba164 "vfs,mm: fix return value of read() at s_maxbytes" need be backported with this patch, otherwise we'll get an error when reading at the end of the file. Thanks, Wei On 2017/2/16 6:41, Ben Hutchings wrote: > 3.16.40-rc1 review patch. If anyone has any objections, please let me know. > > ------------------ > > From: Wei Fang > > commit c2a9737f45e27d8263ff9643f994bda9bac0b944 upstream. > > We triggered a deadloop in truncate_inode_pages_range() on 32 bits > architecture with the test case bellow: > > ... > fd = open(); > write(fd, buf, 4096); > preadv64(fd, &iovec, 1, 0xffffffff000); > ftruncate(fd, 0); > ... > > Then ftruncate() will not return forever. > > The filesystem used in this case is ubifs, but it can be triggered on > many other filesystems. > > When preadv64() is called with offset=0xffffffff000, a page with > index=0xffffffff will be added to the radix tree of ->mapping. Then > this page can be found in ->mapping with pagevec_lookup(). After that, > truncate_inode_pages_range(), which is called in ftruncate(), will fall > into an infinite loop: > > - find a page with index=0xffffffff, since index>=end, this page won't > be truncated > > - index++, and index become 0 > > - the page with index=0xffffffff will be found again > > The data type of index is unsigned long, so index won't overflow to 0 on > 64 bits architecture in this case, and the dead loop won't happen. > > Since truncate_inode_pages_range() is executed with holding lock of > inode->i_rwsem, any operation related with this lock will be blocked, > and a hung task will happen, e.g.: > > INFO: task truncate_test:3364 blocked for more than 120 seconds. > ... > call_rwsem_down_write_failed+0x17/0x30 > generic_file_write_iter+0x32/0x1c0 > ubifs_write_iter+0xcc/0x170 > __vfs_write+0xc4/0x120 > vfs_write+0xb2/0x1b0 > SyS_write+0x46/0xa0 > > The page with index=0xffffffff added to ->mapping is useless. Fix this > by checking the read position before allocating pages. > > Link: http://lkml.kernel.org/r/1475151010-40166-1-git-send-email-fangwei1@huawei.com > Signed-off-by: Wei Fang > Cc: Christoph Hellwig > Cc: Dave Chinner > Cc: Al Viro > Signed-off-by: Andrew Morton > Signed-off-by: Linus Torvalds > [bwh: Backported to 3.16: adjust context] > Signed-off-by: Ben Hutchings > --- > mm/filemap.c | 4 ++++ > 1 file changed, 4 insertions(+) > > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1464,6 +1464,10 @@ static ssize_t do_generic_file_read(stru > unsigned int prev_offset; > int error = 0; > > + if (unlikely(*ppos >= inode->i_sb->s_maxbytes)) > + return -EINVAL; > + iov_iter_truncate(iter, inode->i_sb->s_maxbytes); > + > index = *ppos >> PAGE_CACHE_SHIFT; > prev_index = ra->prev_pos >> PAGE_CACHE_SHIFT; > prev_offset = ra->prev_pos & (PAGE_CACHE_SIZE-1); >