linux-kernel - Re: [PATCH v2 0/9] procfs: protect /proc/<pid>/* files with file->f

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Message-ID: <20131002143759.GA2966@dztty>
Date:	Wed, 2 Oct 2013 15:37:59 +0100
From:	Djalal Harouni <tixxdz@...ndz.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Kees Cook <keescook@...omium.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Serge E. Hallyn" <serge.hallyn@...ntu.com>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	David Rientjes <rientjes@...gle.com>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	tixxdz@...il.com
Subject: Re: [PATCH v2 0/9] procfs: protect /proc/<pid>/* files with
 file->f_cred

On Tue, Oct 01, 2013 at 06:40:41PM -0700, Andy Lutomirski wrote:
> On 10/01/2013 01:26 PM, Djalal Harouni wrote:
> > /proc/<pid>/* entries varies at runtime, appropriate permission checks
> > need to happen during each system call.
> > 
> > Currently some of these sensitive entries are protected by performing
> > the ptrace_may_access() check. However even with that the /proc file
> > descriptors can be passed to a more privileged process
> > (e.g. a suid-exec) which will pass the classic ptrace_may_access()
> > check. In general the ->open() call will be issued by an unprivileged
> > process while the ->read(),->write() calls by a more privileged one.
> > 
> > Example of these files are:
> > /proc/*/syscall, /proc/*/stack etc.
> > 
> > And any open(/proc/self/*) then suid-exec to read()/write() /proc/self/*
> > 
> > 
> > These files are protected during read() by the ptrace_may_access(),
> > however the file descriptor can be passed to a suid-exec which can be
> > used to read data and bypass ASLR. Of course this was discussed several
> > times on LKML.
> 
> Can you elaborate on what it is that you're fixing?  That is, can you
> give a concrete example of what process opens what file and passes the
> fd to what process?
Yes, the references were already given in this email:
https://lkml.org/lkml/2013/8/31/209

This has been discussed several times on lkml:
https://lkml.org/lkml/2013/8/28/544

https://lkml.org/lkml/2013/8/28/564 (check Kees's references)


> I'm having trouble following your description.
Process open a /proc file and pass the fd to a more privilaged process
that will pass the ptrace_may_access() check, while the original process
that opened that file should fail at the ptrace_may_access()


> --Andy
> 

-- 
Djalal Harouni
http://opendz.org
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