Re: [RFC][PATCH 7/7][v4] SI_TKILL: Masquerade si_pid when crossing pid ns boundary

Oleg Nesterov
2008-12-24T15:57:27Z

On 12/24, Sukadev Bhattiprolu wrote:
>
> --- a/kernel/signal.c
> +++ b/kernel/signal.c
> @@ -2385,17 +2385,22 @@ static int do_tkill(pid_t tgid, pid_t pid, int sig)
> struct siginfo info;
> struct task_struct *p;
> unsigned long flags;
> + struct pid_namespace *ns;
>
> error = -ESRCH;
> info.si_signo = sig;
> info.si_errno = 0;
> info.si_code = SI_TKILL;
> - info.si_pid = task_tgid_vnr(current);
> info.si_uid = current_uid();
>
> rcu_read_lock();
> p = find_task_by_vpid(pid);
> if (p && (tgid <= 0 || task_tgid_vnr(p) == tgid)) {
> + ns = task_active_pid_ns(p);
> + if (ns)
> + info.si_pid = task_tgid_nr_ns(current, ns);
> + else
> + info.si_pid = task_tgid_vnr(current);

if ns == 0, "p" won't see the signal anyway, so all we need is

- info.si_pid = task_tgid_vnr(current);
+ info.si_pid = task_tgid_nr_ns(current, task_active_ns(p));

like we do in __do_notify().

But. this of course doesn't work for sys_kill(). Can't we change the helpers
which send SI_FROMUSER() signals so that they do not fill .si_pid at all?
Then send_signal() can do:

default:
copy_siginfo(&q->info, info);
info.si_pid = 0;
if (!from_ancestot_ns)
info.si_pid = task_tgid_nr_ns(current, ...);

?

Yes, we use "current". But we already used it in siginfo_from_ancestor_ns().

Oleg.