[PATCH 7/7][v7] proc: Show SIG_DFL signals to init as "ignored" signals

[Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>]

From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Sat, 17 Jan 2009 09:26:26 -0800
Subject: [PATCH 7/7][v7] proc: Show SIG_DFL signals to init as "ignored" signals

Init processes ignore SIG_DFL signals unless they are from an ancestor
namespace.  Ensure /proc/pid/status correcly reports these signals.

Values for "normal" /bin/bash from /proc/pid/status:

	SigIgn: 0000000000384004
	SigCgt: 000000004b813efb

	Signals 9, 16, 19 etc are neither ignored nor caught

/bin/bash as container-init, Status viewed from outside container:

	SigIgn: 0000000000384004
	SigCgt: 000000004b813efb

	(same as 'normal')

/bin/bash as container-init, Status viewed from inside container:

	SigIgn: ffffffffb47ec104
	SigCgt: 000000004b813efb

	All "uncaught" signals, including SIGKILL(9) SIGSTOP(19) are ignored.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---
 fs/proc/array.c |   18 +++++++++++++++++-
 1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 7e4877d..16e39db 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -228,15 +228,31 @@ static void render_sigset_t(struct seq_file *m, const char *header,
 	seq_printf(m, "\n");
 }
 
+static int is_unkillable(struct task_struct *p)
+{
+	if (!(p->signal->flags & SIGNAL_UNKILLABLE))
+		return 0;
+
+	/* If caller is an ancestor, we are not unkillable */
+	if (task_pid_nr_ns(current, task_active_pid_ns(p)) <= 0)
+		return 0;
+
+	return 1;
+}
+
 static void collect_sigign_sigcatch(struct task_struct *p, sigset_t *ign,
 				    sigset_t *catch)
 {
 	struct k_sigaction *k;
 	int i;
+	int unkillable;
+	
+	unkillable = is_unkillable(p);
 
 	k = p->sighand->action;
 	for (i = 1; i <= _NSIG; ++i, ++k) {
-		if (k->sa.sa_handler == SIG_IGN)
+		if (k->sa.sa_handler == SIG_IGN ||
+				(k->sa.sa_handler == SIG_DFL && unkillable))
 			sigaddset(ign, i);
 		else if (k->sa.sa_handler != SIG_DFL)
 			sigaddset(catch, i);
-- 
1.5.2.5