proc_fork_connector: a lockless ->real_parent usage is not safe

proc_fork_connector() uses ->real_parent lockless.  This is not safe if
copy_process() was called with CLONE_THREAD or CLONE_PARENT, in this case
the parent != current can go away at any moment.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Vladimir Zapolskiy <vzapolskiy@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Evgeniy Polyakov <johnpol@2ka.mipt.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 2 deletions

diff --git a/drivers/connector/cn_proc.c b/drivers/connector/cn_proc.c
index 3ee1fdb31ea7..e55814bc0d06 100644
--- a/drivers/connector/cn_proc.c
+++ b/drivers/connector/cn_proc.c
@@ -57,6 +57,7 @@ void proc_fork_connector(struct task_struct *task)
         struct proc_event *ev;
         __u8 buffer[CN_PROC_MSG_SIZE];
         struct timespec ts;
+        struct task_struct *parent;
 
         if (atomic_read(&proc_event_num_listeners) < 1)
                 return;
@@ -67,8 +68,11 @@ void proc_fork_connector(struct task_struct *task)
         ktime_get_ts(&ts); /* get high res monotonic timestamp */
         put_unaligned(timespec_to_ns(&ts), (__u64 *)&ev->timestamp_ns);
         ev->what = PROC_EVENT_FORK;
-        ev->event_data.fork.parent_pid = task->real_parent->pid;
-        ev->event_data.fork.parent_tgid = task->real_parent->tgid;
+        rcu_read_lock();
+        parent = rcu_dereference(task->real_parent);
+        ev->event_data.fork.parent_pid = parent->pid;
+        ev->event_data.fork.parent_tgid = parent->tgid;
+        rcu_read_unlock();
         ev->event_data.fork.child_pid = task->pid;
         ev->event_data.fork.child_tgid = task->tgid;