Re: [SECURITY] FDs 0, 1, 2 for SUID/SGID programs

From: Remco Post (r.post@sara.nl)
Date: Tue Apr 23 2002 - 08:57:08 EST

Hi,

having thought about this problem for a day or so, I don't think this is
a kernel issue. One cannot simply solve typical userland problems in the
OS. The only proper way to solve this is for apps to check that fd 0 1 2
are open before they open any file or try to write to any of those fd's.
Maybe the code that is executed before main is called can perform these
checks, but certainly not a kernel...

Guess that from now on app developers will have to do even more checking
on their environment before they use it...

On Tue, 23 Apr 2002 14:02:39 +0200
"Alex Riesen" <Alexander.Riesen@synopsys.com> wrote:

> > is nothing specified when it comes to closed file descpriptors
> > across execve(), notably FD's 0, 1 and 2 are certainly not required
> > to be open across an execve() of a SUID/SGID applictaion. One could
> > argue that SUID/SGID apps that trust the file descriptors they
> > inherit across exec() are buggy.
> >
> > Having said that, there are a number of implementations of this type
> > of protection for the linux kernel stemming from the Openwall
> > project. If you are interested, see:
> >
> > http://www.openwall.com (CONFIG_SECURE_FD_0_1_2)
> > http://lsm.immunix.org (CONFIG_OWLSM_FD)
> > http://grsecurity.net (CONFIG_GRKERNSEC_FD)
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-- 
Met vriendelijke groeten,

Remco Post

SARA - Stichting Academisch Rekencentrum Amsterdam    http://www.sara.nl
High Performance Computing  Tel. +31 20 592 8008    Fax. +31 20 668 3167

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