On 29/11/19 19:01, Dr. David Alan Gilbert wrote:
>> It's not entirely trivial because fsdev-proxy-helper wants to keep the
>> effective set and clear the permitted set; in libcap-ng you can only
^^^^^
(Wrong, this is "modify" the permitted set. The permitted set is
already cleared by setresuid/setresgid).
>> apply both sets at once, and you cannot choose only one of them in
>> capng_clear/capng_get_caps_process. But it's doable, I'll take a look.
> I'm having some difficulties making the same conversion for virtiofsd;
> all it wants to do is drop (and later recover) CAP_FSETID
> from it's effective set; so I'm calling capng_get_caps_process
> (it used to be cap_get_proc). While libcap survives just using the
> capget syscall, libcap-ng wants to read /proc/<TID>/status - and
> that's a problem because we're in a sandbox without /proc mounted
> at that point.
The state of libcap-ng persists after capng_apply. So you can just call
capng_update({CAP_ADD,CAP_DROP}) followed by capng_apply.
Does virtiofsd have to do uid/gid dances like virtfs-proxy-helper?
Thanks,
Paolo
