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


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