signals: add from_ancestor_ns parameter to send_signal()

send_signal() (or its helper) needs to determine the pid namespace of the
sender.  But a signal sent via kill_pid_info_as_uid() comes from within
the kernel and send_signal() does not need to determine the pid namespace
of the sender.  So define a helper for send_signal() which takes an
additional parameter, 'from_ancestor_ns' and have kill_pid_info_as_uid()
use that helper directly.

The 'from_ancestor_ns' parameter will be used in a follow-on patch.
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>

kernel/signal.c

@@ -823,8 +823,8 @@ static inline int legacy_queue(struct sigpending *signals, int sig)
 	return (sig < SIGRTMIN) && sigismember(&signals->signal, sig);
 }
 
-static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
-			int group)
+static int __send_signal(int sig, struct siginfo *info, struct task_struct *t,
+			int group, int from_ancestor_ns)
 {
 	struct sigpending *pending;
 	struct sigqueue *q;
@@ -899,6 +899,12 @@ out_set:
 	return 0;
 }
 
+static int send_signal(int sig, struct siginfo *info, struct task_struct *t,
+			int group)
+{
+	return __send_signal(sig, info, t, group, 0);
+}
+
 int print_fatal_signals;
 
 static void print_fatal_signal(struct pt_regs *regs, int signr)
@@ -1143,7 +1149,7 @@ int kill_pid_info_as_uid(int sig, struct siginfo *info, struct pid *pid,
 	if (sig && p->sighand) {
 		unsigned long flags;
 		spin_lock_irqsave(&p->sighand->siglock, flags);
-		ret = __group_send_sig_info(sig, info, p);
+		ret = __send_signal(sig, info, p, 1, 0);
 		spin_unlock_irqrestore(&p->sighand->siglock, flags);
 	}
 out_unlock: