Re: [RFC][PATCH 6/7][v4] SI_USER: Masquerade si_pid when crossing pid ns boundary

Oleg Nesterov
2008-12-24T15:45:22Z

On 12/24, Sukadev Bhattiprolu wrote:
>
> +static void masquerade_si_pid(struct task_struct *t, siginfo_t *info)
> +{
> + if (is_si_special(info) || SI_FROMKERNEL(info))
> + return;
> +
> + /*
> + * When crossing pid namespace boundary, SI_USER signal can only
> + * go from ancestor to descendant ns but not the other way. So,
> + * just ->si_pid to 0 since, the sender will not have a pid in
> + * the receiver's namespace.
> + */
> + if (info->si_code == SI_USER)
> + info->si_pid = 0;
> +}
> +
> static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
> int group)
> {
> @@ -946,6 +974,8 @@ static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
> break;
> default:
> copy_siginfo(&q->info, info);
> + if (from_ancestor_ns)
> + masquerade_si_pid(t, &q->info);
> break;
> }
> } else if (!is_si_special(info)) {
> @@ -2343,7 +2373,7 @@ sys_kill(pid_t pid, int sig)
> info.si_signo = sig;
> info.si_errno = 0;
> info.si_code = SI_USER;
> - info.si_pid = task_tgid_vnr(current);
> + info.si_pid = 0; /* masquerade in send_signal() */
> info.si_uid = current_uid();

Can't understand this patch. First of all, it looks wrong. Looks like
we never set .si_pid != 0 when the signal is set by sys_kill() ?

But more importantly, unless I missed something, this patch is unnecessary
complication.

We call masquerade_si_pid() only when from_ancestor_ns == T, this is correct.
But this means that (!is_si_special(info) && SI_FROMUSER(info)) == T, why
do we re-check in masquerade_si_pid() ?

And why can't we just do

default:
copy_siginfo(&q->info, info);
if (from_ancestor_ns)
info->si_pid = 0;

? Why should we check SI_USER and change sys_kill() ?

see also the comment for the next 7/7 patch.

Oleg.