netdev - Re: [PATCH net,v4] netlink: fix potential sleeping issue in mqueue_flush

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Date: Mon, 22 Jan 2024 19:10:37 +0800
From: shaozhengchao <shaozhengchao@...wei.com>
To: Pablo Neira Ayuso <pablo@...filter.org>
CC: <netdev@...r.kernel.org>, <davem@...emloft.net>, <edumazet@...gle.com>,
	<kuba@...nel.org>, <pabeni@...hat.com>, <horms@...nel.org>,
	<anjali.k.kulkarni@...cle.com>, <kuniyu@...zon.com>, <fw@...len.de>,
	<weiyongjun1@...wei.com>, <yuehaibing@...wei.com>
Subject: Re: [PATCH net,v4] netlink: fix potential sleeping issue in
 mqueue_flush_file



On 2024/1/22 16:56, Pablo Neira Ayuso wrote:
> On Mon, Jan 22, 2024 at 09:18:07AM +0800, Zhengchao Shao wrote:
>> I analyze the potential sleeping issue of the following processes:
>> Thread A                                Thread B
>> ...                                     netlink_create  //ref = 1
>> do_mq_notify                            ...
>>    sock = netlink_getsockbyfilp          ...     //ref = 2
>>    info->notify_sock = sock;             ...
>> ...                                     netlink_sendmsg
>> ...                                       skb = netlink_alloc_large_skb  //skb->head is vmalloced
>> ...                                       netlink_unicast
>> ...                                         sk = netlink_getsockbyportid //ref = 3
>> ...                                         netlink_sendskb
>> ...                                           __netlink_sendskb
>> ...                                             skb_queue_tail //put skb to sk_receive_queue
>> ...                                         sock_put //ref = 2
>> ...                                     ...
>> ...                                     netlink_release
>> ...                                       deferred_put_nlk_sk //ref = 1
>> mqueue_flush_file
>>    spin_lock
>>    remove_notification
>>      netlink_sendskb
>>        sock_put  //ref = 0
>>          sk_free
>>            ...
>>            __sk_destruct
>>              netlink_sock_destruct
>>                skb_queue_purge  //get skb from sk_receive_queue
>>                  ...
>>                  __skb_queue_purge_reason
>>                    kfree_skb_reason
>>                      __kfree_skb
>>                      ...
>>                      skb_release_all
>>                        skb_release_head_state
>>                          netlink_skb_destructor
>>                            vfree(skb->head)  //sleeping while holding spinlock
>>
>> In netlink_sendmsg, if the memory pointed to by skb->head is allocated by
>> vmalloc, and is put to sk_receive_queue queue, also the skb is not freed.
>> When the mqueue executes flush, the sleeping bug will occur. Use
>> vfree_atomic instead of vfree in netlink_skb_destructor to solve the issue.
> 
> mqueue notification is of NOTIFY_COOKIE_LEN size:
> 
> static int do_mq_notify(mqd_t mqdes, const struct sigevent *notification)
> {
>          [...]
>                  if (notification->sigev_notify == SIGEV_THREAD) {
>                          long timeo;
> 
>                          /* create the notify skb */
>                          nc = alloc_skb(NOTIFY_COOKIE_LEN, GFP_KERNEL);
>                          if (!nc)
>                                  return -ENOMEM;
> 
> Do you have a reproducer?
Hi Pablo:
	I donot have reproducer. I found the issue when running syz on
the 5.10 stable branch, but it only happened once. Then I analyzed the
mainline code and found the same issue.
	The sock can be obtained from the value of sigev_signo
transferred by the user in do_mq_notify. And the sock may be of type
netlink, and it is possible to allocate the head area using vmalloc.
Not only release the skb allocated in do_mq_notify, but also release
the skb allocated in netlink_sendmsg when put sock mqueue_flush_file.
What I missed?
Thank you.

Zhengchao Shao