linux-kernel - [PATCH] procfs: fix missing RCU protection when reading real_parent in do_task

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Message-ID: <20260127150450.2073236-1-alexjlzheng@tencent.com>
Date: Tue, 27 Jan 2026 23:04:50 +0800
From: alexjlzheng@...il.com
To: oleg@...hat.com,
	usamaarif642@...il.com,
	david@...nel.org,
	akpm@...ux-foundation.org,
	lorenzo.stoakes@...cle.com,
	alexjlzheng@...cent.com,
	mingo@...nel.org,
	ruippan@...cent.com
Cc: linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: [PATCH] procfs: fix missing RCU protection when reading real_parent in do_task_stat()

From: Jinliang Zheng <alexjlzheng@...cent.com>

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

  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!
      task_pid_ptr    <--- UAF!
      rcu_read_unlock

This fix adds proper RCU protection similar to getppid() in kernel/sys.c
which correctly uses rcu_dereference() when accessing current->real_parent.

Fixes: 06fffb1267c9 ("do_task_stat: don't take rcu_read_lock()")
Signed-off-by: Jinliang Zheng <alexjlzheng@...cent.com>
---
 fs/proc/array.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/proc/array.c b/fs/proc/array.c
index 42932f88141a..3c2eea2c551a 100644
--- a/fs/proc/array.c
+++ b/fs/proc/array.c
@@ -528,7 +528,9 @@ 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);
+		rcu_read_lock();
+		ppid = task_tgid_nr_ns(rcu_dereference(task->real_parent), ns);
+		rcu_read_unlock();
 		pgid = task_pgrp_nr_ns(task, ns);
 
 		unlock_task_sighand(task, &flags);
-- 
2.39.3