[PATCH 4.4 78/86] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

[Greg Kroah-Hartman]

From: Eddy Wu <itseddy0...@gmail.com>

commit b4e00444cab4c3f3fec876dc0cccc8cbb0d1a948 upstream.

current->group_leader->exit_signal may change during copy_process() if
current->real_parent exits.

Move the assignment inside tasklist_lock to avoid the race.

Signed-off-by: Eddy Wu <eddy...@trendmicro.com>
Acked-by: Oleg Nesterov <o...@redhat.com>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 kernel/fork.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1539,14 +1539,9 @@ static struct task_struct *copy_process(
        /* ok, now we should be set up.. */
        p->pid = pid_nr(pid);
        if (clone_flags & CLONE_THREAD) {
-               p->exit_signal = -1;
                p->group_leader = current->group_leader;
                p->tgid = current->tgid;
        } else {
-               if (clone_flags & CLONE_PARENT)
-                       p->exit_signal = current->group_leader->exit_signal;
-               else
-                       p->exit_signal = (clone_flags & CSIGNAL);
                p->group_leader = p;
                p->tgid = p->pid;
        }
@@ -1591,9 +1586,14 @@ static struct task_struct *copy_process(
        if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) {
                p->real_parent = current->real_parent;
                p->parent_exec_id = current->parent_exec_id;
+               if (clone_flags & CLONE_THREAD)
+                       p->exit_signal = -1;
+               else
+                       p->exit_signal = current->group_leader->exit_signal;
        } else {
                p->real_parent = current;
                p->parent_exec_id = current->self_exec_id;
+               p->exit_signal = (clone_flags & CSIGNAL);
        }
 
        spin_lock(&current->sighand->siglock);