Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and make it readable

[Cyrill Gorcunov <gorcunov-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Mon, Jan 26, 2015 at 04:15:26PM -0800, Kees Cook wrote:
> >
> > akpm3:/usr/src/25> grep -r map_files Documentation
> 
> If akpm's comments weren't clear: this needs to be fixed. Everything
> in /proc should appear in Documentation.

I'll do that.

> > The 640708a2cff7f81 changelog says:
> >
> > :     This one behaves similarly to the /proc/<pid>/fd/ one - it contains
> > :     symlinks one for each mapping with file, the name of a symlink is
> > :     "vma->vm_start-vma->vm_end", the target is the file.  Opening a symlink
> > :     results in a file that point exactly to the same inode as them vma's one.
> > :
> > :     For example the ls -l of some arbitrary /proc/<pid>/map_files/
> > :
> > :      | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80403000-7f8f80404000 -> /lib64/libc-2.5.so
> > :      | lr-x------ 1 root root 64 Aug 26 06:40 7f8f8061e000-7f8f80620000 -> /lib64/libselinux.so.1
> > :      | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80826000-7f8f80827000 -> /lib64/libacl.so.1.1.0
> > :      | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a2f000-7f8f80a30000 -> /lib64/librt-2.5.so
> > :      | lr-x------ 1 root root 64 Aug 26 06:40 7f8f80a30000-7f8f80a4c000 -> /lib64/ld-2.5.so
> 
> How is mmap offset represented in this output?

We're printing vm_area_struct:[vm_start;vm_end] only.

> > afacit this info is also available in /proc/pid/maps, so things
> > shouldn't get worse if the /proc/pid/map_files permissions are at least
> > as restrictive as the /proc/pid/maps permissions.  Is that the case?
> > (Please add to changelog).
> 
> Both maps and map_files uses ptrace_may_access (via mm_acces) with
> PTRACE_MODE_READ, so I'm happy from a info leak perspective.
> 
> Are mount namespaces handled in this output?

Could you clarify this moment, i'm not sure i get it.

> 
> > 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?