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

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Date:	Tue, 01 Oct 2013 18:40:41 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Djalal Harouni <tixxdz@...ndz.org>
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 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?

I'm having trouble following your description.

--Andy

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