Re: [patch 2/2] fs, proc: Introduce the /proc/<pid>/map_files/ directoryv12

[Pavel Emelyanov]

> 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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