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Date: Sun, 11 Mar 2012 01:27:25 +0100
From: Djalal Harouni <tixxdz@...ndz.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
Andrew Morton <akpm@...ux-foundation.org>,
Al Viro <viro@...iv.linux.org.uk>,
Alexey Dobriyan <adobriyan@...il.com>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Vasiliy Kulikov <segoon@...nwall.com>,
Kees Cook <keescook@...omium.org>,
Solar Designer <solar@...nwall.com>,
WANG Cong <xiyou.wangcong@...il.com>,
James Morris <james.l.morris@...cle.com>,
Oleg Nesterov <oleg@...hat.com>,
linux-security-module@...r.kernel.org,
linux-fsdevel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>,
Greg KH <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...e.hu>,
Stephen Wilson <wilsons@...rt.ca>,
"Jason A. Donenfeld" <Jason@...c4.com>
Subject: Re: [PATCH 0/9] proc: protect /proc/<pid>/* files across execve
On Sat, Mar 10, 2012 at 04:01:09PM -0800, Linus Torvalds wrote:
> On Sat, Mar 10, 2012 at 3:25 PM, Djalal Harouni <tixxdz@...ndz.org> wrote:
> >
> > 1) Use the target exec_id to bind files to their exec_id task:
> >
> > For the REG files /proc/<pid>/{environ,pagemap,mem} we set the exec_id
> > of the proc_file_private to the target task, and we continue with
> > permission checks at open time, later on each read/write call the
> > permission checks are done + check the target exec_id if it equals the
> > exec_id of the proc_file_private that was set at open time, in other words
> > we bind the file to its task's exec_id, this way new exec programs can not
> > operate on the passed fd.
>
> So the exec_id approach was totally broken when it was used for
> /proc/<pid>/mem, is there any reason to believe it's a good idea now?
Yes the previously one was broken since it was not a global uniq exec_id,
it was designed for threads tracking.
The current one is a global exec_id with uniq IDs, incremented on each
do_execve_common() call.
> It's entirely predictable, and you can make the exec_id match by
> simply forking elsewhere and then passing the fd around using unix
> domain sockets, since the exec_id is just updated by incrementing a
> counter.
For the fork one yes exec_id will match but we have the permission
checks (ptrace) at each syscall, so even if two processes share the same
exec_id the ptrace check should fail.
Yes it's predictable, but I don't see how you could pass the fd to another
extern privileged process without failing at the exec_id check.
--
tixxdz
http://opendz.org
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