[PATCH AUTOSEL 5.4 42/42] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real_parent

[Sasha Levin]

From: Eddy Wu <itseddy0402@xxxxxxxxx>

[ Upstream commit b4e00444cab4c3f3fec876dc0cccc8cbb0d1a948 ]

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: Sasha Levin <sashal@xxxxxxxxxx>
---
 kernel/fork.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/fork.c b/kernel/fork.c
index e3d5963d8c6f5..419fff8eb9e55 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2100,14 +2100,9 @@ static __latent_entropy 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 = args->exit_signal;
 		p->group_leader = p;
 		p->tgid = p->pid;
 	}
@@ -2152,9 +2147,14 @@ static __latent_entropy 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 = args->exit_signal;
 	}
 
 	klp_copy_process(p);
-- 
2.27.0