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

[Xiaoming Ni]

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)" <ki...@tencent.com>
Link: https://www.openwall.com/lists/oss-security/2020/11/01/1
Cc: <sta...@vger.kernel.org> #v3.11
Signed-off-by: Xiaoming Ni <nixiaom...@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