linux-kernel - Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map

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Message-ID: <20150127072323.GI651@moon>
Date:	Tue, 27 Jan 2015 10:23:23 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Calvin Owens <calvinowens@...com>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Peter Feiner <pfeiner@...gle.com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Siddhesh Poyarekar <siddhesh.poyarekar@...il.com>,
	linux-kernel@...r.kernel.org, kernel-team@...com,
	Pavel Emelyanov <xemul@...nvz.org>, linux-api@...r.kernel.org,
	Kees Cook <keescook@...omium.org>
Subject: Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and
 make it readable

On Mon, Jan 26, 2015 at 10:50:23PM -0800, Andrew Morton wrote:
> On Tue, 27 Jan 2015 09:46:47 +0300 Cyrill Gorcunov <gorcunov@...il.com> wrote:
> 
> > > There's one other problem here: we're assuming that the map_files
> > > implementation doesn't have bugs.  If it does have bugs then relaxing
> > > permissions like this will create new vulnerabilities.  And the
> > > map_files implementation is surprisingly complex.  Is it bug-free?
> > 
> > I didn't find any bugs in map-files (and we use it for long time already)
> > so I think it is safe.
> 
> You've been using map_files the way it was supposed to be used so no,
> any bugs won't show up.  What happens if you don your evil black hat
> and use map_files in ways that weren't anticipated?  Attack it?

Hard to say, Andrew. If I found a way to exploit this feature for
bad purpose for sure I would patch it out. At the moment I don't
see any. Touching another process memory via file descriptor
allows one to modify its contents but you have to be granted
ptrace-may-access which i consider as enough for security.
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