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

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Message-ID: <4E70D29D.20104@parallels.com>
Date:	Wed, 14 Sep 2011 20:13:17 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
CC:	Cyrill Gorcunov <gorcunov@...il.com>, Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm00@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"containers@...ts.osdl.org" <containers@...ts.osdl.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Kirill Shutemov <kirill@...temov.name>,
	James Bottomley <jbottomley@...allels.com>,
	Nathan Lynch <ntl@...ox.com>, Zan Lynx <zlynx@....org>,
	Daniel Lezcano <dlezcano@...ibm.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

> No, I mean something else.  Assume you have a task, which does the
> steps:
> 
> 1) opens some sensitive file as root.  This file is e.g. 0700.
> 
> 2) mmaps the file via opened fd, either RO or RW.
> 
> 3) closes fd.
> 
> 4) drops root.
> 
> Now it has a mapping of a privileged file, but cannot get fd of it
> anyhow.  With map_files/ he may open his own /proc/$$/map_files/, pass
> ptrace() check, and get fd of the privileged file.  He cannot explicitly
> open it as it is 0700, but he may open it via map_files/ and get RO/RW
> fd.
> 

What is the problem here - the fact that we have some file considered to
be private be open-able by somebody else, or the fact that we can truncate
the file being mapped?

If the fist issue stands, then it also stands for /proc/pid/fd and thus we
don't introduce the new problem.

If the second, then it's not a problem as mm can handle this already.

Thanks,
Pavel
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