linux-kernel - Re: [PATCH -next] cgroup: fix uaf when proc_cpuset

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Date: Mon, 24 Jun 2024 11:34:02 +0800
From: chenridong <chenridong@...wei.com>
To: Markus Elfring <Markus.Elfring@....de>, <cgroups@...r.kernel.org>,
	<bpf@...r.kernel.org>, Johannes Weiner <hannes@...xchg.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 -next] cgroup: fix uaf when proc_cpuset_show


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