net: lib: coap: fix potential null pointer

In coap_well_known_core_get(), move the null check for 'resource' before
applying pointer arithmetic ('resource + 1') to avoid undefined behavior
when 'resource == NULL'.

Signed-off-by: Gaetan Perrot <[email protected]>

Author: moonlight83340

subsys/net/lib/coap/coap_link_format.c

@@ -695,13 +695,15 @@ int coap_well_known_core_get(struct coap_resource *resource,
 			     struct coap_packet *response,
 			     uint8_t *data, uint16_t data_len)
 {
-	struct coap_resource *resources = resource + 1;
+	struct coap_resource *resources;
 	size_t resources_len = 0;
 
 	if (resource == NULL) {
 		return -EINVAL;
 	}
 
+	resources = resource + 1;
+
 	while (resources[resources_len].path) {
 		resources_len++;
 	}