Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933610AbcJUJTp (ORCPT ); Fri, 21 Oct 2016 05:19:45 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:46908 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933558AbcJUJTf (ORCPT ); Fri, 21 Oct 2016 05:19:35 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Wei Fang , Christoph Hellwig , Dave Chinner , Al Viro , Andrew Morton , Linus Torvalds Subject: [PATCH 4.7 32/45] vfs,mm: fix a dead loop in truncate_inode_pages_range() Date: Fri, 21 Oct 2016 11:17:52 +0200 Message-Id: <20161021091428.971169669@linuxfoundation.org> X-Mailer: git-send-email 2.10.0 In-Reply-To: <20161021091427.214431885@linuxfoundation.org> References: <20161021091427.214431885@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2629 Lines: 82 4.7-stable 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 Signed-off-by: Greg Kroah-Hartman --- mm/filemap.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/mm/filemap.c +++ b/mm/filemap.c @@ -1609,6 +1609,10 @@ 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_SHIFT; prev_index = ra->prev_pos >> PAGE_SHIFT; prev_offset = ra->prev_pos & (PAGE_SIZE-1);