linux-kernel - [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting ->real

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Date:   Sat, 7 Nov 2020 14:47:22 +0800
From:   Eddy Wu <itseddy0402@...il.com>
To:     oleg@...hat.com
Cc:     security@...nel.org, linux-kernel@...r.kernel.org,
        eddy_wu@...ndmicro.com
Subject: [PATCH] fork: fix copy_process(CLONE_PARENT) race with the exiting
 ->real_parent

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

diff --git a/kernel/fork.c b/kernel/fork.c
index da8d360fb032..7abda2a888a9 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -2142,14 +2142,9 @@ 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;
 	}
@@ -2193,9 +2188,14 @@ 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);
-- 
2.17.1