Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/directory v12

[Cyrill Gorcunov]

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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