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

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Date:	Thu, 15 Sep 2011 14:29:22 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Vasiliy Kulikov <segoon@...nwall.com>
Cc:	Pavel Machek <pavel@....cz>, 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>,
	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 Thu, Sep 15, 2011 at 01:27:57PM +0400, Vasiliy Kulikov wrote:
...
> 
> > in case two of them has a mapping shared, we map
> >    the memory by the 1st one and then open its /proc/$pid/map_files/address file and
> >    map it by the 2nd task.
> 
> How can you restore a set of processes in case they share an RW mapping
> as RW in both tasks if you deny opening /proc/$pid/map_files/$address as W?

I can read the link first to figure out the file path and re-open it as rw via
path itself (which implies the restorer still must have enough rights to open
it as rw).

> 
> > Using /proc/$pid/maps for this is quite inconvenient since it brings repeatable
> > re-reading and reparsing for this text file which slows down restore procesure
> > significantly. Also as being pointed in (3) it is a way easier to use top level
> > shared mapping in children as /proc/$pid/map_files/address when needed.
> [...]
> > v14: (by Vasiliy Kulikov)
> >  - for security reason the links are created with FMODE_READ mode
> >    only even if the former file has FMODE_WRITE
> >  - proc_map_files_lookup fails on any non-read-only queries.
> 
> Do you have a PoC of the dumper?  At least without the restorer.  If we
> see an implementation of map_files/ user we probably identify what
> operation it needs and what security restrictions we have to define.

Yeah, i'll ping you the link (while beign trying various approaches
the code end up in being a pure mess, so until all cleaned up and
works as expected i'll not public it).

	Cyrill
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