linux-kernel - Re: [PATCH] cgroup/cpuset: Prevent UAF in proc_cpuset

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Date: Sat, 22 Jun 2024 22:04:22 +0200
From: Markus Elfring <Markus.Elfring@....de>
To: Waiman Long <longman@...hat.com>, Chen Ridong <chenridong@...wei.com>,
 cgroups@...r.kernel.org, bpf@...r.kernel.org,
 Johannes Weiner <hannes@...xchg.org>, Tejun Heo <tj@...nel.org>,
 Zefan Li <lizefan.x@...edance.com>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cgroup/cpuset: Prevent UAF in proc_cpuset_show()

…
> +++ b/kernel/cgroup/cpuset.c
…
> @@ -5051,10 +5066,12 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
>  	if (!buf)
>  		goto out;
>
> +	mutex_lock(&cpuset_mutex);
>  	css = task_get_css(tsk, cpuset_cgrp_id);
>  	retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
>  				current->nsproxy->cgroup_ns);
>  	css_put(css);
> +	mutex_unlock(&cpuset_mutex);
…

Under which circumstances would you become interested to apply a statement
like “guard(mutex)(&cpuset_mutex);”?
https://elixir.bootlin.com/linux/v6.10-rc4/source/include/linux/mutex.h#L196

Regards,
Markus