[PATCH 2/4] signals: send_signal: use si_fromuser() to detect from_ancestor_ns

[Oleg Nesterov <oleg@redhat.com>]

Change send_signal() to use si_fromuser(). From now SEND_SIG_NOINFO
triggers the "from_ancestor_ns" check.

This fixes reparent_thread()->group_send_sig_info(pdeath_signal)
behaviour, before this patch send_signal() does not detect the
cross-namespace case when the child of the dying parent belongs
to the sub-namespace.

This patch can affect the behaviour of send_sig(), kill_pgrp() and
kill_pid() when the caller sends the signal to the sub-namespace
with "priv == 0" but surprisingly all callers seem to use them
correctly, including disassociate_ctty(on_exit).

Except: drivers/staging/comedi/drivers/addi-data/*.c incorrectly
use send_sig(priv => 0). But his is minor and should be fixed
anyway.

Reported-by: Daniel Lezcano <dlezcano@fr.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---

 kernel/signal.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

--- TTT_32/kernel/signal.c~FU_2_SEND_SIGNAL	2009-10-04 02:21:55.000000000 +0200
+++ TTT_32/kernel/signal.c	2009-10-04 03:09:44.000000000 +0200
@@ -928,9 +928,8 @@ static int send_signal(int sig, struct s
 	int from_ancestor_ns = 0;
 
 #ifdef CONFIG_PID_NS
-	if (!is_si_special(info) && SI_FROMUSER(info) &&
-			task_pid_nr_ns(current, task_active_pid_ns(t)) <= 0)
-		from_ancestor_ns = 1;
+	from_ancestor_ns = si_fromuser(info) &&
+			   !task_pid_nr_ns(current, task_active_pid_ns(t));
 #endif
 
 	return __send_signal(sig, info, t, group, from_ancestor_ns);