From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932591Ab3KIGvb (ORCPT ); Sat, 9 Nov 2013 01:51:31 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:33136 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932231Ab3KIGvR (ORCPT ); Sat, 9 Nov 2013 01:51:17 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Jiaxing Wang , Gu Zheng , Al Viro , Jonghwan Choi Subject: [PATCH 3.10 70/74] seq_file: always update file->f_pos in seq_lseek() Date: Fri, 8 Nov 2013 22:52:15 -0800 Message-Id: <20131109065118.388161189@linuxfoundation.org> X-Mailer: git-send-email 1.8.5.rc0.dirty In-Reply-To: <20131109065113.502217951@linuxfoundation.org> References: <20131109065113.502217951@linuxfoundation.org> User-Agent: quilt/0.60-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Gu Zheng commit 05e16745c0c471bba313961b605b6da3b21a853d upstream. This issue was first pointed out by Jiaxing Wang several months ago, but no further comments: https://lkml.org/lkml/2013/6/29/41 As we know pread() does not change f_pos, so after pread(), file->f_pos and m->read_pos become different. And seq_lseek() does not update file->f_pos if offset equals to m->read_pos, so after pread() and seq_lseek()(lseek to m->read_pos), then a subsequent read may read from a wrong position, the following program produces the problem: char str1[32] = { 0 }; char str2[32] = { 0 }; int poffset = 10; int count = 20; /*open any seq file*/ int fd = open("/proc/modules", O_RDONLY); pread(fd, str1, count, poffset); printf("pread:%s\n", str1); /*seek to where m->read_pos is*/ lseek(fd, poffset+count, SEEK_SET); /*supposed to read from poffset+count, but this read from position 0*/ read(fd, str2, count); printf("read:%s\n", str2); out put: pread: ck_netbios_ns 12665 read: nf_conntrack_netbios /proc/modules: nf_conntrack_netbios_ns 12665 0 - Live 0xffffffffa038b000 nf_conntrack_broadcast 12589 1 nf_conntrack_netbios_ns, Live 0xffffffffa0386000 So we always update file->f_pos to offset in seq_lseek() to fix this issue. Signed-off-by: Jiaxing Wang Signed-off-by: Gu Zheng Signed-off-by: Al Viro Cc: Jonghwan Choi Signed-off-by: Greg Kroah-Hartman --- fs/seq_file.c | 2 ++ 1 file changed, 2 insertions(+) --- a/fs/seq_file.c +++ b/fs/seq_file.c @@ -328,6 +328,8 @@ loff_t seq_lseek(struct file *file, loff m->read_pos = offset; retval = file->f_pos = offset; } + } else { + file->f_pos = offset; } } file->f_version = m->version;