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

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

quoted

-----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) <redacted>;
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)" <redacted>
Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
Cc: <redacted> #v3.11
Signed-off-by: Xiaoming Ni <redacted>
---
  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