Implement a simple check to see if a specified pid resides
in a specified pid namespace.  Generally we are smart enough
just to operate on single pid namespace and avoid this test.
However in the case of sending a signal to init we must check
to see if our sender is a child of init and so this test is needed.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
---
 include/linux/pid.h |    3 +++
 kernel/pid.c        |    6 ++++++
 2 files changed, 9 insertions(+), 0 deletions(-)

diff --git a/include/linux/pid.h b/include/linux/pid.h
index c4b56c0..e409cc5 100644
--- a/include/linux/pid.h
+++ b/include/linux/pid.h
@@ -156,6 +156,9 @@ static inline pid_t pid_nr(struct pid *pid)
 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns);
 pid_t pid_vnr(struct pid *pid);
 
+/* Test to see if pid is present in pid namespace ns */
+extern int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns);
+
 #define do_each_pid_task(pid, type, task)				\
 	do {								\
 		struct hlist_node *pos___;				\
diff --git a/kernel/pid.c b/kernel/pid.c
index a7ecfce..873c00f 100644
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -429,6 +429,12 @@ struct pid *find_get_pid(pid_t nr)
 	return pid;
 }
 
+int pid_in_pid_ns(struct pid *pid, struct pid_namespace *ns)
+{
+	return pid && ns && (ns->level <= pid->level) &&
+		pid->numbers[ns->level].ns == ns;
+}
+
 pid_t pid_nr_ns(struct pid *pid, struct pid_namespace *ns)
 {
 	struct upid *upid;
-- 
1.5.3.rc6.17.g1911

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