pid namespaces: destroy pid namespace on init's death

Terminate all processes in a namespace when the reaper of the namespace is
exiting.  We do this by walking the pidmap of the namespace and sending
SIGKILL to all processes.

Signed-off-by: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Acked-by: Pavel Emelyanov <xemul@openvz.org>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 26 insertions, 1 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index d9e8e5ee9d7f..567909fd6be4 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -879,7 +879,32 @@ static inline void exit_child_reaper(struct task_struct *tsk)
         if (likely(tsk->group_leader != task_child_reaper(tsk)))
                 return;
 
-        panic("Attempted to kill init!");
+        if (tsk->nsproxy->pid_ns == &init_pid_ns)
+                panic("Attempted to kill init!");
+
+        /*
+         * @tsk is the last thread in the 'cgroup-init' and is exiting.
+         * Terminate all remaining processes in the namespace and reap them
+         * before exiting @tsk.
+         *
+         * Note that @tsk (last thread of cgroup-init) may not necessarily
+         * be the child-reaper (i.e main thread of cgroup-init) of the
+         * namespace i.e the child_reaper may have already exited.
+         *
+         * Even after a child_reaper exits, we let it inherit orphaned children,
+         * because, pid_ns->child_reaper remains valid as long as there is
+         * at least one living sub-thread in the cgroup init.
+
+         * This living sub-thread of the cgroup-init will be notified when
+         * a child inherited by the 'child-reaper' exits (do_notify_parent()
+         * uses __group_send_sig_info()). Further, when reaping child processes,
+         * do_wait() iterates over children of all living sub threads.
+
+         * i.e even though 'child_reaper' thread is listed as the parent of the
+         * orphaned children, any living sub-thread in the cgroup-init can
+         * perform the role of the child_reaper.
+         */
+        zap_pid_ns_processes(tsk->nsproxy->pid_ns);
 }
 
 fastcall NORET_TYPE void do_exit(long code)