From: Waiman Long <longman@redhat.com>
Date: Tue, 2 Sep 2025 18:15:37 +0000 (-0400)
Subject: cgroup/cpuset: Prevent NULL pointer access in free_tmpmasks()
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=e117ff1129daa7d63536833f39285e50ad52379d;p=users%2Fhch%2Fmisc.git

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@quicinc.com>
Closes: https://lore.kernel.org/lkml/20250902-cpuset-free-on-condition-v1-1-f46ffab53eac@quicinc.com/
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---

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);