From mboxrd@z Thu Jan 1 00:00:00 1970 From: Amerigo Wang Subject: Re: [Patch v3] vfs: allow file truncations when both suid and write permissions set Date: Mon, 10 Aug 2009 10:30:06 +0800 Message-ID: <4A7F862E.9020501@redhat.com> References: <20090807100743.5822.90612.sendpatchset@localhost.localdomain> <1249675025.2694.15.camel@dhcp231-106.rdu.redhat.com> <87prb7v0dr.fsf@devron.myhome.or.jp> <1249677481.2694.22.camel@dhcp231-106.rdu.redhat.com> <87eirnqrbj.fsf@devron.myhome.or.jp> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Eric Paris , linux-kernel@vger.kernel.org, esandeen@redhat.com, eteo@redhat.com, linux-fsdevel@vger.kernel.org, akpm@linux-foundation.org, viro@zeniv.linux.org.uk, sds@tycho.nsa.gov, linux-security-module@vger.kernel.org To: OGAWA Hirofumi Return-path: In-Reply-To: <87eirnqrbj.fsf@devron.myhome.or.jp> Sender: linux-security-module-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org OGAWA Hirofumi wrote: > Eric Paris writes: > > >>>> 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 >>>> >>> BTW, Do you know why doesn't security modules fix the handling of >>> do_truncate() (i.e. ATTR_MODE | ATTR_SIZE). And why doesn't it allow to >>> pass ATTR_FORCE for it? >>> >> I'm not sure what you mean. I understood ATTR_FORCE to mean 'I am magic >> and get to override all security checks." Which is why nothing should >> ever be using ATTR_FORCE with things other than SUID. >> >> I guess we could somehow force logic into the LSM to make it only apply >> to SUID and friends but I'm not sure it buys us anything. >> > > Yes, I think it's good way. Don't we want to do the following? > > if (permission check of job) > return error; > if (do job at once) > return error; > > But currently way is, > > if (permission check of first part) > return error > if (do first part of job) > return error > if (permission check of second part) > return error > if (do second part of job) > return error > > So, if second part was error, we may want to undo the job of first part > in theory. But, to undo is just hard and strange. > Yeah, the problem is currently we don't have such wrappers, only notify_change(). :-/