[PATCH 6.6 150/283] procfs: fix missing RCU protection when reading real_parent in do_task_stat()

Sasha Levin
2026-02-28T18:09:15Z

From: Jinliang Zheng <alexjlzheng@tencent.com>

[ Upstream commit 76149d53502cf17ef3ae454ff384551236fba867 ]

When reading /proc/[pid]/stat, do_task_stat() accesses task->real_parent
without proper RCU protection, which leads to:

cpu 0 cpu 1
----- -----
do_task_stat
var = task->real_parent
release_task
call_rcu(delayed_put_task_struct)
task_tgid_nr_ns(var)
rcu_read_lock <--- Too late to protect task->real_parent!
task_pid_ptr <--- UAF!
rcu_read_unlock

This patch uses task_ppid_nr_ns() instead of task_tgid_nr_ns() to add
proper RCU protection for accessing task->real_parent.

Link: https://lkml.kernel.org/r/20260128083007.3173016-1-alexjlzheng@tencent.com
Fixes: 06fffb1267c9 ("do_task_stat: don't take rcu_read_lock()")
Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Mateusz Guzik <mjguzik@gmail.com>
Cc: ruippan <ruippan@tencent.com>
Cc: Usama Arif <usamaarif642@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/proc/array.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 5e4f7b411fbdb..363d9331216b9 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -531,7 +531,7 @@ static int do_task_stat(struct seq_file *m, struct pid_namespace *ns,
}

sid = task_session_nr_ns(task, ns);
- ppid = task_tgid_nr_ns(task->real_parent, ns);
+ ppid = task_ppid_nr_ns(task, ns);
pgid = task_pgrp_nr_ns(task, ns);

unlock_task_sighand(task, &flags);
--
2.51.0