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

From: Oleg Nesterov
Date: Wed Oct 31 2018 - 11:49:38 EST

On 10/31, Daniel Colascione wrote:
> > Confused... why? kill_ok_by_cred() should fail?
> Not if we don't run it. :-) I thought you were proposing that we do
> *all* access checks in open() and let write() succeed unconditionally,

Ah, no ;)

> Anyway, I sent a v2 patch that I think closes the hole another way. In
> v2, we just require that the real user ID that opens a /proc/pid/kill
> file is the same one that writes to it. It successfully blocks the
> setuid attack above while preserving all the write-time permission
> checks and keeping the close correspondence between
> write()-on-proc-pid-kill-fd and kill(2). Can you think of any
> situation where this scheme breaks?

I see no problems...

but again, perhaps we should fix kill_pid_info_as_cred() and use it in
/proc/pid/kill? I dunno.