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

[chenridong]

On 2024/6/22 21:45, Markus Elfring wrote:
> > 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?
Thank you for review, i will do that.
> …
> > +++ 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

We hope somebody could have another better solution.

Regards

Ridong