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

Sukadev Bhattiprolu
2008-12-24T21:10:38Z

Oleg Nesterov [oleg@redhat.com] wrote:
| 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;

Grr, This needs to go. I started with a general function but then
got specific to SI_USER.

| > +
| > + /*
| > + * 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();

Yes, I will undo this...

|
| 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;

and go with this.

|
| ? Why should we check SI_USER and change sys_kill() ?
|
| see also the comment for the next 7/7 patch.
|
| Oleg.