[PATCH 4.19 56/71] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

From: Greg Kroah-Hartman
Date: Mon Nov 09 2020 - 08:31:07 EST


From: Eddy Wu <itseddy0402@xxxxxxxxx>

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_wu@xxxxxxxxxxxxxx>
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

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

--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1965,14 +1965,9 @@ static __latent_entropy struct task_stru
/* 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;
}
@@ -2017,9 +2012,14 @@ static __latent_entropy struct task_stru
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);
}

klp_copy_process(p);