linux-kernel - Re: [PATCH 8/9] proc: protect /proc/<pid>/{environ,pagemap} across execve

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Message-ID: <20120311170125.GA10787@dztty>
Date:	Sun, 11 Mar 2012 18:01:25 +0100
From:	Djalal Harouni <tixxdz@...ndz.org>
To:	Alexey Dobriyan <adobriyan@...il.com>
Cc:	linux-kernel@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	"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 8/9] proc: protect /proc/<pid>/{environ,pagemap} across
 execve

On Sun, Mar 11, 2012 at 11:05:23AM +0300, Alexey Dobriyan wrote:
> On Sun, Mar 11, 2012 at 12:25:18AM +0100, Djalal Harouni wrote:
> > The /proc/<pid>/{environ,pagemap} are sensitive files which must be
> > protected across execve to avoid information leaks.
> > 
> > These files are protected by attaching them to their task at open time by
> > saving the exec_id of the target task, this way in read we just compare
> > the target task's exec_id and the previously saved exec_id of the
> > proc_file_private struct, in other words we just bind these files to their
> > appropriate process image at open time. We do this since we are able to do
> > proper permission checks (ptrace) at each syscall, so we do not care about
> > the reader.
> > 
> > Another important rule is to set the exec_id of the target task before the
> > permission checks at open, this way we do not race against target task
> > execve, and it will be more effective if the exec_id check at read/write
> > times are delayed as much as possible to be sure that the target task do
> > not change during execve.
> > 
> > This patch adds the open file_operation to the
> > /proc/<pid>/{environ,pagemap} so we are able to set the exec_id of the
> > target task and to do the appropriate permission checks. The exec_id check
> > is done in the related read file_operation.
> 
> ->open is duplicated.
Right, I'll unify the code in a generic open function that does:
* alloc and setup proc_file_private (which includes the exec_id)
* ptrace check using mm_for_maps()
  unify only those who check PTRACE_MODE_READ
* save priv_file_proc.

This applies also to the release functions, I'll re-submit it.

Thanks Alexey.

-- 
tixxdz
http://opendz.org
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