linux-kernel - Re: [PATCH] Check files' signatures before doing suid/sgid [2/4]

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Date:	Thu, 21 Jun 2007 11:49:48 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Alexander Wuerstlein <snalwuer@....informatik.uni-erlangen.de>
Cc:	linux-kernel@...r.kernel.org, arw@....name
Subject: Re: [PATCH] Check files' signatures before doing suid/sgid [2/4]

On Thu, 2007-06-21 at 19:46 +0200, Alexander Wuerstlein wrote:
> On 070621 19:33, Arjan van de Ven <arjan@...radead.org> wrote:
> > On Thu, 2007-06-21 at 19:25 +0200, Alexander Wuerstlein wrote:
> > > On 070621 19:21, Arjan van de Ven <arjan@...radead.org> wrote:
> > > > On Thu, 2007-06-21 at 18:02 +0200, Alexander Wuerstlein wrote:
> > > > > Modified task_struct to hold a 'signed flag' which is set on exec(), inherited
> > > > > on fork() and checked during exec before giving the new process suid/sgid
> > > > > privileges.
> > > > > 
> > > > 
> > > > 
> > > > 
> > > > do you also check the signature of glibc and every other shared library
> > > > that the app uses (or dlopens)? if not.. the entire exercise is rather
> > > > pointless...
> > > 
> > > We do check that, that is patch [3/4].
> > > 
> > > Of course we can only check mmap-ed files, if there is no file like with JIT
> > > compilers we are out of luck.
> > 
> > or if the process uses read() not mmap().
> 
> If a process uses read() it needs some executable and writable memory. We do
> check for this in mprotect(). There is a problem with the i386-architecture,
> because it allows execution of any readable page (except with newer
> processors). But beyond that ugliness of i386, it should not be possible to
> execute anything without us noticing it (hopefully).

welcome to mprotect() where the app can just change the permissions

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
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