signals: zap_pid_ns_process() should use force_sig()

send_signal() assumes that signals with SEND_SIG_PRIV are generated from
within the same namespace.  So any nested container-init processes become
immune to the SIGKILL generated by kill_proc_info() in
zap_pid_ns_processes().

Use force_sig() in zap_pid_ns_processes() instead - force_sig() clears the
SIGNAL_UNKILLABLE flag ensuring the signal is processed by
container-inits.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Daniel Lezcano <daniel.lezcano@free.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 14 insertions, 1 deletions

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index fab8ea86fac3..2d1001b4858d 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -152,6 +152,7 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
 {
         int nr;
         int rc;
+        struct task_struct *task;
 
         /*
          * The last thread in the cgroup-init thread group is terminating.
@@ -169,7 +170,19 @@ void zap_pid_ns_processes(struct pid_namespace *pid_ns)
         read_lock(&tasklist_lock);
         nr = next_pidmap(pid_ns, 1);
         while (nr > 0) {
-                kill_proc_info(SIGKILL, SEND_SIG_PRIV, nr);
+                rcu_read_lock();
+
+                /*
+                 * Use force_sig() since it clears SIGNAL_UNKILLABLE ensuring
+                 * any nested-container's init processes don't ignore the
+                 * signal
+                 */
+                task = pid_task(find_vpid(nr), PIDTYPE_PID);
+                if (task)
+                        force_sig(SIGKILL, task);
+
+                rcu_read_unlock();
+
                 nr = next_pidmap(pid_ns, nr);
         }
         read_unlock(&tasklist_lock);