Re: [PATCH bpf-next 4/4] bpf, sockmap: Fix double uncharge the mem of sk_msg

[wangyufen <wangyufen@huawei.com>]

在 2022/3/1 12:11, John Fastabend 写道:
> Wang Yufen wrote:
>> If tcp_bpf_sendmsg is running during a tear down operation, psock may be
>> freed.
>>
>> tcp_bpf_sendmsg()
>>   tcp_bpf_send_verdict()
>>    sk_msg_return()
>>    tcp_bpf_sendmsg_redir()
>>     unlikely(!psock))
>>     sk_msg_free()
>>
>> The mem of msg has been uncharged in tcp_bpf_send_verdict() by
>> sk_msg_return(), so we need to use sk_msg_free_nocharge while psock
>> is null.
>>
>> This issue can cause the following info:
>> WARNING: CPU: 0 PID: 2136 at net/ipv4/af_inet.c:155 inet_sock_destruct+0x13c/0x260
>> Call Trace:
>>   <TASK>
>>   __sk_destruct+0x24/0x1f0
>>   sk_psock_destroy+0x19b/0x1c0
>>   process_one_work+0x1b3/0x3c0
>>   worker_thread+0x30/0x350
>>   ? process_one_work+0x3c0/0x3c0
>>   kthread+0xe6/0x110
>>   ? kthread_complete_and_exit+0x20/0x20
>>   ret_from_fork+0x22/0x30
>>   </TASK>
>>
>> Fixes: 604326b41a6f ("bpf, sockmap: convert to generic sk_msg interface")
>> Signed-off-by: Wang Yufen <wangyufen@huawei.com>
>> ---
>>   net/ipv4/tcp_bpf.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/net/ipv4/tcp_bpf.c b/net/ipv4/tcp_bpf.c
>> index 1f0364e06619..03c037d2a055 100644
>> --- a/net/ipv4/tcp_bpf.c
>> +++ b/net/ipv4/tcp_bpf.c
>> @@ -139,7 +139,7 @@ int tcp_bpf_sendmsg_redir(struct sock *sk, struct sk_msg *msg,
>>   	int ret;
>>   
>>   	if (unlikely(!psock)) {
>> -		sk_msg_free(sk, msg);
>> +		sk_msg_free_nocharge(sk, msg);
>>   		return 0;
>>   	}
>>   	ret = ingress ? bpf_tcp_ingress(sk, psock, msg, bytes, flags) :
> Did you consider simply returning an error code here? This would then
> trigger the sk_msg_free_nocharge in the error path of __SK_REDIRECT
> and would have the side effect of throwing an error up to user space.
> This would be a slight change in behavior from user side but would
> look the same as an error if the redirect on the socket threw an
> error so I think it would be OK.

Yes, I think it would be better to return -EPIPE,  will do in v2.

Thanks.

>
> Thanks,
> John
> .