linux-kernel - [PATCH] cgroup/cpuset: Prevent NULL pointer access in free

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Message-ID: <20250902181537.833102-1-longman@redhat.com>
Date: Tue,  2 Sep 2025 14:15:37 -0400
From: Waiman Long <longman@...hat.com>
To: Tejun Heo <tj@...nel.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Koutný <mkoutny@...e.com>
Cc: cgroups@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ashay Jaiswal <quic_ashayj@...cinc.com>,
	Chen Ridong <chenridong@...wei.com>,
	Waiman Long <longman@...hat.com>
Subject: [PATCH] cgroup/cpuset: Prevent NULL pointer access in free_tmpmasks()

Commit 5806b3d05165 ("cpuset: decouple tmpmasks and cpumasks freeing in
cgroup") separates out the freeing of tmpmasks into a new free_tmpmask()
helper but removes the NULL pointer check in the process. Unfortunately a
NULL pointer can be passed to free_tmpmasks() in cpuset_handle_hotplug()
if cpuset v1 is active. This can cause segmentation fault and crash
the kernel.

Fix that by adding the NULL pointer check to free_tmpmasks().

Fixes: 5806b3d05165 ("cpuset: decouple tmpmasks and cpumasks freeing in cgroup")
Reported-by: Ashay Jaiswal <quic_ashayj@...cinc.com>
Closes: https://lore.kernel.org/lkml/20250902-cpuset-free-on-condition-v1-1-f46ffab53eac@quicinc.com/
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/cgroup/cpuset.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index a78ccd11ce9b..c0c281a8860d 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -484,6 +484,9 @@ static inline int alloc_tmpmasks(struct tmpmasks *tmp)
  */
 static inline void free_tmpmasks(struct tmpmasks *tmp)
 {
+	if (!tmp)
+		return;
+
 	free_cpumask_var(tmp->new_cpus);
 	free_cpumask_var(tmp->addmask);
 	free_cpumask_var(tmp->delmask);
-- 
2.50.1