signals: SI_USER: Masquerade si_pid when crossing pid ns boundary

When sending a signal to a descendant namespace, set ->si_pid to 0 since
the sender does not have a pid in the receiver's namespace.

Note:
	- If rt_sigqueueinfo() sets si_code to SI_USER when sending a
	  signal across a pid namespace boundary, the value in ->si_pid
	  will be cleared to 0.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/signal.c b/kernel/signal.c
index ba3da25..d803473 100644 (file)
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -883,6 +883,8 @@ static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
                        break;
                default:
                        copy_siginfo(&q->info, info);
+                       if (from_ancestor_ns)
+                               q->info.si_pid = 0;
                        break;
                }
        } else if (!is_si_special(info)) {