Re: [RFC PATCH] Implement /proc/pid/kill

From: Oleg Nesterov
Date: Wed Oct 31 2018 - 11:10:13 EST

On 10/31, Daniel Colascione wrote:
> > perhaps it would be simpler to do
> >
> > my_cred = override_creds(file->f_cred);
> > kill_pid(...);
> > revert_creds(my_cred);
> Thanks for the suggestion. That looks neat, but it's not quite enough.
> The problem is that check_kill_permission looks for
> same_thread_group(current, t) _before_ checking kill_of_by_cred,

Yes, you are right.

Looks like kill_pid_info_as_cred() can find another user, but probably
it needs some changes with or without /proc/pid/kill ...

> There's another problem though: say we open /proc/pid/5/kill *, with
> proc 5 being an ordinary unprivileged process, e.g., the shell. At
> open(2) time, the access check passes. Now suppose PID 5 execve(2)s
> into a setuid process. The kill FD is still open, so the kill FD's
> holder can send a signal

Confused... why? kill_ok_by_cred() should fail?