Re: [PATCH 4/4] nfc: Avoid endless loops caused by repeated llcp_sock_connect()(Internet mail)

[Xiaoming Ni <nixiaoming@huawei.com>]

On 2021/3/3 17:28, kiyin(尹亮) wrote:
> Hi xiaoming,
>    the path can only fix the endless loop problem. it can't fix the meaningless llcp_sock->service_name problem.
>    if we set llcp_sock->service_name to meaningless string, the connect will be failed. and sk->sk_state will not be LLCP_CONNECTED. then we can call llcp_sock_connect() many times. that leaks everything: llcp_sock->dev, llcp_sock->local, llcp_sock->ssap, llcp_sock->service_name...

I didn't find the code to modify sk->sk_state after a connect failure. 
Can you provide guidance?

Based on my understanding of the current code:
After llcp_sock_connect() is invoked using the meaningless service_name 
as the parameter, sk->sk_state is set to LLCP_CONNECTING. After that, no 
corresponding service responds to the request because the service_name 
is meaningless, the value of sk->sk_state remains unchanged.
Therefore, when llcp_sock_connect() is invoked again, resources such as 
llcp_sock->service_name are not repeatedly applied because sk_state is 
set to LLCP_CONNECTING.

In this way, the repeated invoking of llcp_sock_connect() does not 
repeatedly leak resources.

Thanks
Xiaoming Ni


> 
>> -----Original Message-----
>> From: Xiaoming Ni [mailto:nixiaoming@huawei.com]
>> Sent: Wednesday, March 3, 2021 2:17 PM
>> To: linux-kernel@vger.kernel.org; kiyin(尹亮) <kiyin@tencent.com>;
>> stable@vger.kernel.org; gregkh@linuxfoundation.org; sameo@linux.intel.com;
>> linville@tuxdriver.com; davem@davemloft.net; kuba@kernel.org;
>> mkl@pengutronix.de; stefan@datenfreihafen.org;
>> matthieu.baerts@tessares.net; netdev@vger.kernel.org
>> Cc: nixiaoming@huawei.com; wangle6@huawei.com; xiaoqian9@huawei.com
>> Subject: [PATCH 4/4] nfc: Avoid endless loops caused by repeated
>> llcp_sock_connect()(Internet mail)
>>
>> When sock_wait_state() returns -EINPROGRESS, "sk->sk_state" is
>> LLCP_CONNECTING. In this case, llcp_sock_connect() is repeatedly invoked,
>>   nfc_llcp_sock_link() will add sk to local->connecting_sockets twice.
>>   sk->sk_node->next will point to itself, that will make an endless loop  and
>> hang-up the system.
>> To fix it, check whether sk->sk_state is LLCP_CONNECTING in
>>   llcp_sock_connect() to avoid repeated invoking.
>>
>> fix CVE-2020-25673
>> Fixes: b4011239a08e ("NFC: llcp: Fix non blocking sockets connections")
>> Reported-by: "kiyin(尹亮)" <kiyin@tencent.com>
>> Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
>> Cc: <stable@vger.kernel.org> #v3.11
>> Signed-off-by: Xiaoming Ni <nixiaoming@huawei.com>
>> ---
>>   net/nfc/llcp_sock.c | 4 ++++
>>   1 file changed, 4 insertions(+)
>>
>> diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c index
>> 59172614b249..a3b46f888803 100644
>> --- a/net/nfc/llcp_sock.c
>> +++ b/net/nfc/llcp_sock.c
>> @@ -673,6 +673,10 @@ static int llcp_sock_connect(struct socket *sock,
>> struct sockaddr *_addr,
>>   		ret = -EISCONN;
>>   		goto error;
>>   	}
>> +	if (sk->sk_state == LLCP_CONNECTING) {
>> +		ret = -EINPROGRESS;
>> +		goto error;
>> +	}
>>
>>   	dev = nfc_get_device(addr->dev_idx);
>>   	if (dev == NULL) {
>> --
>> 2.27.0
>>
>