linux-kernel - Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map

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Date:	Wed, 14 Sep 2011 15:39:12 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Pavel Machek <pavel@....cz>
Cc:	Andrew Morton <akpm00@...il.com>, linux-kernel@...r.kernel.org,
	containers@...ts.osdl.org, linux-fsdevel@...r.kernel.org,
	Kirill Shutemov <kirill@...temov.name>,
	Pavel Emelyanov <xemul@...allels.com>,
	James Bottomley <jbottomley@...allels.com>,
	Nathan Lynch <ntl@...ox.com>, Zan Lynx <zlynx@....org>,
	Daniel Lezcano <dlezcano@...ibm.com>,
	Vasiliy Kulikov <segoon@...nwall.com>,
	Tejun Heo <tj@...nel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Al Viro <viro@...IV.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/
 directory v12

On Wed, Sep 14, 2011 at 01:14:38PM +0200, Pavel Machek wrote:
> Hi!
> 
...
> > 
> > Pavel, I somehow lost. What exactly the security issue here? There are a few
> > patches from Vasiliy in -mm queue at moment. In particular one includes
> > .permission set for fd/ handling. So I've updated the map_files as well
> > (it's below). So please review and point me where the problem
> > is. Thanks!
> 
> AFAICT, this recreates existing problem with /proc/<pid>/fd (see
> discussion at 
> 
> http://www.securityfocus.com/archive/1/507386/30/0/threaded
> 
> ). It creates object that looks like symlink, but does not behave as
> one, and permissions of directories are not checked as they would be
> if it was a symlink.
> 
> 									Pavel

OK, so the problem is that we might return a path to the file mapped
even if the directory which consists the former file has its permission
changed, right? For example, lets say we have

| lr-x------ 1 cyrill cyrill 64 Sep 14 19:35 /proc/self/map_files/3d73a00000-3d73a1c000 -> /lib64/ld-2.5.so

and once /lib64 became unreadable we should not return the path to
3d73a00000-3d73a1c000 as well, that is what you mean, right?

	Cyrill
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