Re: [PATCH -next] cgroup: fix uaf when proc_cpuset_show

[Markus Elfring]

> We found a refcount UAF bug as follows:
>
> BUG: KASAN: use-after-free in cgroup_path_ns+0x112/0x150
…

How do you think about to use a summary phrase like “Avoid use-after-free
in proc_cpuset_show()”?


> This is also reported by: https://syzkaller.appspot.com/bug?extid=9b1ff7be974a403aa4cd

Would you like to add any tags (like “Fixes”) accordingly?


…
> +++ b/kernel/cgroup/cpuset.c
…
> @@ -5052,9 +5053,28 @@ int proc_cpuset_show(struct seq_file *m, struct pid_namespace *ns,
>  		goto out;
>
>  	css = task_get_css(tsk, cpuset_cgrp_id);
> +	rcu_read_lock();
…
> +	rcu_read_unlock();
>  	retval = cgroup_path_ns(css->cgroup, buf, PATH_MAX,
>  				current->nsproxy->cgroup_ns);
…

Would you become interested to apply a statement like “guard(rcu_read_lock)();”?
https://elixir.bootlin.com/linux/v6.10-rc4/source/include/linux/cleanup.h#L133

Regards,
Markus