linux-kernel - Re: [PATCH V4] cgroup/cpuset: Prevent UAF in proc_cpuset

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Date: Sun, 30 Jun 2024 11:20:58 +0200
From: Markus Elfring <Markus.Elfring@....de>
To: Chen Ridong <chenridong@...wei.com>, cgroups@...r.kernel.org,
 Aditya Kali <adityakali@...gle.com>, Johannes Weiner <hannes@...xchg.org>,
 Michal Koutný <mkoutny@...e.com>,
 Serge Hallyn <sergeh@...nel.org>, Tejun Heo <tj@...nel.org>,
 Waiman Long <longman@...hat.com>, Zefan Li <lizefan.x@...edance.com>
Cc: LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4] cgroup/cpuset: Prevent UAF in proc_cpuset_show()

…
> +++ b/kernel/cgroup/cpuset.c
…
> @@ -5051,10 +5052,14 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
>  	if (!buf)
>  		goto out;
>
> -	css = task_get_css(tsk, cpuset_cgrp_id);
> -	retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
> -				current->nsproxy->cgroup_ns);
> -	css_put(css);
> +	rcu_read_lock();
> +	spin_lock_irq(&css_set_lock);
> +	css = task_css(tsk, cpuset_cgrp_id);
> +	retval = cgroup_path_ns_locked(css->cgroup, buf, PATH_MAX,
> +				       current->nsproxy->cgroup_ns);
> +	spin_unlock_irq(&css_set_lock);
> +	rcu_read_unlock();
…

Under which circumstances would you become interested to apply statements
like the following?

* guard(rcu)();
  https://elixir.bootlin.com/linux/v6.10-rc5/source/include/linux/rcupdate.h#L1093

* guard(spinlock_irq)(&css_set_lock);
  https://elixir.bootlin.com/linux/v6.10-rc5/source/include/linux/spinlock.h#L567


Regards,
Markus