[PATCH 03/12] pid: get ppid pid_t of task in init_pid_ns safely

[Richard Guy Briggs]

Added the functions
        task_ppid()
        task_ppid_nr_ns()
        task_ppid_nr_init_ns()
to safely abstract the lookup of the PPID (real_parent's tgid) of a process,
including rcu locking, in any required pid namespace.  This provides an
alternative to sys_getppid(), which is relative to the child process' pid
namespace.

(informed by ebiederman's 6c621b7e)
Cc: stable at vger.kernel.org
Cc: Eric W. Biederman <ebiederm at xmission.com>
Signed-off-by: Richard Guy Briggs <rgb at redhat.com>
---
 include/linux/sched.h |   23 +++++++++++++++++++++++
 1 files changed, 23 insertions(+), 0 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d722490..ec04090 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1448,6 +1448,11 @@ static inline struct pid *task_session(struct task_struct *task)
 	return task->group_leader->pids[PIDTYPE_SID].pid;
 }
 
+static inline struct pid *task_ppid(struct task_struct *task)
+{
+	return task_tgid(rcu_dereference(current->real_parent));
+}
+
 struct pid_namespace;
 
 /*
@@ -1496,6 +1501,24 @@ static inline pid_t task_tgid_vnr(struct task_struct *tsk)
 }
 
 
+static inline pid_t task_ppid_nr_ns(struct task_struct *tsk,
+					struct pid_namespace *ns)
+{
+	pid_t pid;
+
+	rcu_read_lock();
+	pid = pid_nr_ns(task_ppid(current), ns);
+	rcu_read_unlock();
+
+	return pid;
+}
+
+static inline pid_t task_ppid_nr_init_ns(struct task_struct *tsk)
+{
+	return task_ppid_nr_ns(tsk, &init_pid_ns);
+}
+
+
 static inline pid_t task_pgrp_nr_ns(struct task_struct *tsk,
 					struct pid_namespace *ns)
 {
-- 
1.7.1