pid: get pid_t ppid of task in init_pid_ns

Added the functions task_ppid_nr_ns() and task_ppid_nr() to abstract the lookup
of the PPID (real_parent's pid_t) of a process, including rcu locking, in the
arbitrary and init_pid_ns.
This provides an alternative to sys_getppid(), which is relative to the child
process' pid namespace.

(informed by ebiederman's 6c621b7e)
Cc: stable@vger.kernel.org
Cc: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Richard Guy Briggs <rgb@redhat.com>

1 files changed, 19 insertions, 1 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 53f97eb8dbc7..116e301fb13f 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1561,6 +1561,24 @@ static inline pid_t task_tgid_vnr(struct task_struct *tsk)
 }
 
 
+static int pid_alive(const struct task_struct *p);
+static inline pid_t task_ppid_nr_ns(const struct task_struct *tsk, struct pid_namespace *ns)
+{
+        pid_t pid = 0;
+
+        rcu_read_lock();
+        if (pid_alive(tsk))
+                pid = task_tgid_nr_ns(rcu_dereference(tsk->real_parent), ns);
+        rcu_read_unlock();
+
+        return pid;
+}
+
+static inline pid_t task_ppid_nr(const 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)
 {
@@ -1600,7 +1618,7 @@ static inline pid_t task_pgrp_nr(struct task_struct *tsk)
  *
  * Return: 1 if the process is alive. 0 otherwise.
  */
-static inline int pid_alive(struct task_struct *p)
+static inline int pid_alive(const struct task_struct *p)
 {
         return p->pids[PIDTYPE_PID].pid != NULL;
 }