Should process run under chroot(8) still see mounts on the original system?

[Teske, Devin]

On Jul 23, 2013, at 4:31 PM, Mateusz Guzik wrote:

> On Tue, Jul 23, 2013 at 04:17:02PM -0700, Yuri wrote:
>> Currently, mount directories as shown by mount(8) command and
>> /compat/linux/dev/mounts from linprocfs(5) still show the original
>> mount points as other non-chrooted processes see.
>> So, when some program run under chroot tries to read the mount
>> points and do something with them it would likely fail because those
>> paths aren't what the process actually sees in its file system.
>> 
>> There are two situations: one when the process was started already
>> chrooted (like with command chroot(8)), and another one is when
>> process calls chroot(2) itself. Currently system seems to not
>> differentiate between these two cases.
>> 
>> It looks reasonable to automatically modify mount(8) and
>> linprocfs(5) results when the process has been started already
>> chrooted and this process is (practically) always unaware of chroot.
>> So that when chroot was in place when execve(2), kernel could set
>> the boolean flag and later adjust mount directories accordingly.
>> 
> 
> While changing the code to do what you propose would not be that
> difficult, I don't see the point. In cases like this you can simply
> jail(2) and there you go (or at least this should work just fine).
> 
> Of course then you may have some unnecessary separation but that I
> believe can be simply worked out if it turns out to be problematic.
> 

What the OP wants is implemented for jails via the sysctl ``knob'' "security.jail.enforce_statfs"

It can have one of three values.

0 = show nothing from the base in jailed df(1) output
2 = show everything from the base in jailed df(1) output

What you want sounds like the number in-between:

1 = show only mount points from the base that appear within the jail *and* make the jailed df(1) output show a modified path that is rooted in said jail
-- 
Devin

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