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

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Message-ID: <3c51992e-a61a-4644-b7ac-1daa8ed0e06d@huaweicloud.com>
Date: Wed, 3 Sep 2025 08:39:18 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Waiman Long <longman@...hat.com>, 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>
Subject: Re: [PATCH] cgroup/cpuset: Prevent NULL pointer access in
 free_tmpmasks()



On 2025/9/3 2:15, Waiman Long wrote:
> 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);

Thank you, Longman and Ashay.

My apologies for missing the NULL pointer check, which led to this issue.
I have double-checked the free_cpuset function, and it does not receive a NULL pointer as input.

-- 
Best regards,
Ridong