Re: [patch] unprivileged mounts update

[ebiederm@xmission.com (Eric W. Biederman)]

"Serge E. Hallyn" <serge@hallyn.com> writes:

> Quoting Eric W. Biederman (ebiederm@xmission.com):
>> 
>> Are there other permission checks that mount is doing that we
>> care about.
>
> Not mount itself, but in looking up /share/fa/root/home/fa,
> user fa doesn't have the rights to read /share, and by setting
> fsuid to fa and dropping CAP_DAC_READ_SEARCH the mount action fails.

Got it. 

I'm not certain this is actually a problem it may be a feature.
But it does fly in the face of the general principle of just
getting out of roots way so things can get done.

I think we can solve your basic problem by simply doing like:
chdir(/share); mount(.);  To simply avoid the permission problem.

The practical question is how much do we care.

> But the solution you outlined in your previous post would work around
> this perfectly.

If we are not using usual permissions which user do we use current->uid?
Or do we pass that user someplace?

>> > If it were really the equivalent then I could keep my capabilities :)
>> > after changing it.
>> 
>> We drop all capabilities after we change the euid.
>
> Not if we've done prctl(PR_SET_KEEPCAPS, 1)

Ah cap_clear doesn't do the obvious thing.

Eric