[PATCH net] nfc: llcp: fix -ENOMEM on connect with zero-length service name

["Ömer Mete Kaya" <omermetekaya0@gmail.com>]

When service_name_len is 0, kmemdup() returns ZERO_SIZE_PTR which
passes the NULL check, causing nfc_llcp_send_connect() to attempt
building a zero-length service name TLV and fail with -ENOMEM.

Fix by setting service_name to NULL directly when service_name_len is 0.

Fixes: d646960f7986 ("NFC: Initial LLCP support")
Signed-off-by: Ömer Mete Kaya <omermetekaya0@gmail.com>
---
 net/nfc/llcp_sock.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/net/nfc/llcp_sock.c b/net/nfc/llcp_sock.c
index 5558d8a4d48b..220cd38e253c 100644
--- a/net/nfc/llcp_sock.c
+++ b/net/nfc/llcp_sock.c
@@ -734,12 +734,16 @@ static int llcp_sock_connect(struct socket *sock, struct sockaddr_unsized *_addr
 	llcp_sock->service_name_len = min_t(unsigned int,
 					    addr->service_name_len,
 					    NFC_LLCP_MAX_SERVICE_NAME);
-	llcp_sock->service_name = kmemdup(addr->service_name,
-					  llcp_sock->service_name_len,
-					  GFP_KERNEL);
-	if (!llcp_sock->service_name) {
-		ret = -ENOMEM;
-		goto sock_llcp_release;
+	if (llcp_sock->service_name_len == 0) {
+		llcp_sock->service_name = NULL;
+	} else {
+		llcp_sock->service_name = kmemdup(addr->service_name,
+						  llcp_sock->service_name_len,
+						  GFP_KERNEL);
+		if (!llcp_sock->service_name) {
+			ret = -ENOMEM;
+			goto sock_llcp_release;
+		}
 	}
 
 	nfc_llcp_sock_link(&local->connecting_sockets, sk);
-- 
2.55.0