net: nfc: fix races in nfc_llcp_sock_get() and nfc_llcp_sock_get_sn()

Sili Luo reported a race in nfc_llcp_sock_get(), leading to UAF.

Getting a reference on the socket found in a lookup while
holding a lock should happen before releasing the lock.

nfc_llcp_sock_get_sn() has a similar problem.

Finally nfc_llcp_recv_snl() needs to make sure the socket
found by nfc_llcp_sock_from_sn() does not disappear.

Fixes: 8f50020e ("NFC: LLCP late binding")
Reported-by: Sili Luo <rootlab@huawei.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Link: https://lore.kernel.org/r/20231009123110.3735515-1-edumazet@google.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

net/nfc/llcp_core.c

@@ -203,17 +203,13 @@ static struct nfc_llcp_sock *nfc_llcp_sock_get(struct nfc_llcp_local *local,
 
 		if (tmp_sock->ssap == ssap && tmp_sock->dsap == dsap) {
 			llcp_sock = tmp_sock;
+			sock_hold(&llcp_sock->sk);
 			break;
 		}
 	}
 
 	read_unlock(&local->sockets.lock);
 
-	if (llcp_sock == NULL)
-		return NULL;
-
-	sock_hold(&llcp_sock->sk);
-
 	return llcp_sock;
 }
 
@@ -346,7 +342,8 @@ static int nfc_llcp_wks_sap(const char *service_name, size_t service_name_len)
 
 static
 struct nfc_llcp_sock *nfc_llcp_sock_from_sn(struct nfc_llcp_local *local,
-					    const u8 *sn, size_t sn_len)
+					    const u8 *sn, size_t sn_len,
+					    bool needref)
 {
 	struct sock *sk;
 	struct nfc_llcp_sock *llcp_sock, *tmp_sock;
@@ -382,6 +379,8 @@ struct nfc_llcp_sock *nfc_llcp_sock_from_sn(struct nfc_llcp_local *local,
 
 		if (memcmp(sn, tmp_sock->service_name, sn_len) == 0) {
 			llcp_sock = tmp_sock;
+			if (needref)
+				sock_hold(&llcp_sock->sk);
 			break;
 		}
 	}
@@ -423,7 +422,8 @@ u8 nfc_llcp_get_sdp_ssap(struct nfc_llcp_local *local,
 		 * to this service name.
 		 */
 		if (nfc_llcp_sock_from_sn(local, sock->service_name,
-					  sock->service_name_len) != NULL) {
+					  sock->service_name_len,
+					  false) != NULL) {
 			mutex_unlock(&local->sdp_lock);
 
 			return LLCP_SAP_MAX;
@@ -824,16 +824,7 @@ static struct nfc_llcp_sock *nfc_llcp_connecting_sock_get(struct nfc_llcp_local
 static struct nfc_llcp_sock *nfc_llcp_sock_get_sn(struct nfc_llcp_local *local,
 						  const u8 *sn, size_t sn_len)
 {
-	struct nfc_llcp_sock *llcp_sock;
-
-	llcp_sock = nfc_llcp_sock_from_sn(local, sn, sn_len);
-
-	if (llcp_sock == NULL)
-		return NULL;
-
-	sock_hold(&llcp_sock->sk);
-
-	return llcp_sock;
+	return nfc_llcp_sock_from_sn(local, sn, sn_len, true);
 }
 
 static const u8 *nfc_llcp_connect_sn(const struct sk_buff *skb, size_t *sn_len)
@@ -1298,7 +1289,8 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local,
 			}
 
 			llcp_sock = nfc_llcp_sock_from_sn(local, service_name,
-							  service_name_len);
+							  service_name_len,
+							  true);
 			if (!llcp_sock) {
 				sap = 0;
 				goto add_snl;
@@ -1318,6 +1310,7 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local,
 
 				if (sap == LLCP_SAP_MAX) {
 					sap = 0;
+					nfc_llcp_sock_put(llcp_sock);
 					goto add_snl;
 				}
 
@@ -1335,6 +1328,7 @@ static void nfc_llcp_recv_snl(struct nfc_llcp_local *local,
 
 			pr_debug("%p %d\n", llcp_sock, sap);
 
+			nfc_llcp_sock_put(llcp_sock);
 add_snl:
 			sdp = nfc_llcp_build_sdres_tlv(tid, sap);
 			if (sdp == NULL)