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Message-ID: <CA+55aFwdOgt=C52APPyvnAitcWNbzu-uXRi43m4bLS85oDgtqA@mail.gmail.com>
Date: Sat, 10 Mar 2012 16:01:09 -0800
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Djalal Harouni <tixxdz@...ndz.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 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?
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.
I would in general suggest strongly against using exec_id for anything
that involves files. It isn't designed for that, it's designed for the
whole "check the parent exec_id" thing for ptrace, where that whole
"pass things around to another process" approach doesn't work.
Linus
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