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Message-ID: <1784519.tIOlXC7y92@x2>
Date: Tue, 29 Apr 2014 18:18:58 -0400
From: Steve Grubb <sgrubb@...hat.com>
To: oss-security@...ts.openwall.com
Cc: Solar Designer <solar@...nwall.com>
Subject: Re: local privilege escalation due to capng_lock as used in seunshare
On Wednesday, April 30, 2014 02:12:22 AM Solar Designer wrote:
> On Tue, Apr 29, 2014 at 05:49:04PM -0400, Steve Grubb wrote:
> > On Tuesday, April 29, 2014 02:20:47 PM Andy Lutomirski wrote:
> > > if (setuid(getuid()) != 0)
> > >
> > > err(1, "setuid(getuid())");
> >
> > If you do not want the saved uid to be available, you need to use
> > setresuid. That removes it. I would classify this as a bug in the test
> > program.
>
> Not quite.
If the program was amended to use setresuid(), does the bug still exist?
-Steve
> Per POSIX.1-2001, setuid() "shall set the real user ID, effective user
> ID, and the saved set-user-ID of the calling process to uid" if the
> process has "appropriate privileges". On traditional Unix systems,
> without capabilities, running as root historically does constitute
> "appropriate privileges". If we want current systems to support safely
> running programs written for traditional Unix (including SUID root
> programs), which I think is taken for granted by many of us, we must not
> deviate from those semantics in dangerous ways. Any such deviation is a
> vulnerability in our current kernel code or configuration.
>
> Distributions must not ship with settings or programs that allow anyone
> other than an administrator to alter the definition of "appropriate
> privileges" in a way that, while compliant with this vague wording in
> POSIX, introduces a vulnerability for correct programs written for
> traditional Unix systems.
>
> What we have here is a reincarnation of:
>
> "Sendmail Workaround for Linux Capabilities Bug"
> https://www.sendmail.com/sm/open_source/security/security_docs/sendmail.8.10
> .1.LINUX-SECURITY.txt
>
> albeit in slightly different shape (not entirely in the kernel, but with
> a userland "helper").
>
> I think that sendmail-exposed vulnerability was in the kernel (not in
> sendmail), and I think the vulnerability Andy is reporting is in some
> distros (apparently, Red Hat's).
>
> Of course, it is possible that I have missed something important as I
> did not look into this issue closely, but the above is my current
> understanding based on Andy's message.
>
> Alexander
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