From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933337AbZHGT5n (ORCPT ); Fri, 7 Aug 2009 15:57:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S933314AbZHGT5m (ORCPT ); Fri, 7 Aug 2009 15:57:42 -0400 Received: from mx2.redhat.com ([66.187.237.31]:59779 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933310AbZHGT5l (ORCPT ); Fri, 7 Aug 2009 15:57:41 -0400 Subject: Re: [Patch v3] vfs: allow file truncations when both suid and write permissions set From: Eric Paris To: Amerigo Wang Cc: linux-kernel@vger.kernel.org, esandeen@redhat.com, eteo@redhat.com, linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org, hirofumi@mail.parknet.co.jp, viro@zeniv.linux.org.uk In-Reply-To: <20090807100743.5822.90612.sendpatchset@localhost.localdomain> References: <20090807100743.5822.90612.sendpatchset@localhost.localdomain> Content-Type: text/plain Date: Fri, 07 Aug 2009 15:57:05 -0400 Message-Id: <1249675025.2694.15.camel@dhcp231-106.rdu.redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2009-08-07 at 06:05 -0400, Amerigo Wang wrote: > V2 -> V3: > Call notify_change() before clearing suid/sgid. > Thanks to OGAWA Hirofumi. > > V1 -> V2: > Introduce dentry_remove_suid(), and use it in do_truncate(). > Thanks to Eric Paris. > > > When suid is set and the non-owner user has write permission, > any writing into this file should be allowed and suid should be > removed after that. > > However, current kernel only allows writing without truncations, > when we do truncations on that file, we get EPERM. This is a bug. > > Steps to reproduce this bug: > > % ls -l rootdir/file1 > -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 > % echo h > rootdir/file1 > zsh: operation not permitted: rootdir/file1 > % ls -l rootdir/file1 > -rwsrwsrwx 1 root root 3 Jun 25 15:42 rootdir/file1 > % echo h >> rootdir/file1 > % ls -l rootdir/file1 > -rwxrwxrwx 1 root root 5 Jun 25 16:34 rootdir/file1 > > This patch fixes it. > > Signed-off-by: WANG Cong > Cc: Eric Sandeen > Cc: Eric Paris > Cc: Eugene Teo > Cc: Al Viro > Cc: hirofumi@mail.parknet.co.jp I was thinking about this and kept telling myself I was going to test v2 before I ack/nak. Clearly we shouldn't for the dropping of SUID if the process didn't have permission to change the ATTR_SIZE. Acked-by: Eric Paris