Fix Thread DHCPv6-client memory leak (ARMmbed#1808)

Thread DHCPv6-client is leaking memory if DHCP message sending fails.
Release allocated server and message payload to fix the memory leak.

Author: Arto Kinnunen

source/6LoWPAN/Thread/thread_dhcpv6_client.c

@@ -190,16 +190,19 @@ int thread_dhcp_client_get_global_address(int8_t interface, uint8_t dhcp_addr[st
     }
 
     srv_data_ptr = libdhcvp6_nontemporalAddress_server_data_allocate(interface, dhcp_client.libDhcp_instance, mac64, DHCPV6_DUID_HARDWARE_EUI64_TYPE, prefix, dhcp_addr);
+    if (!srv_data_ptr) {
+        tr_error("OOM srv_data_ptr");
+        return -1;
+    }
 
     payload_len = libdhcpv6_solication_message_length(DHCPV6_DUID_HARDWARE_EUI64_TYPE, true, 0);
     payload_ptr = ns_dyn_mem_temporary_alloc(payload_len);
-
-    if (payload_ptr == NULL || srv_data_ptr == NULL) {
-        ns_dyn_mem_free(payload_ptr);
+    if (!payload_ptr) {
         libdhcvp6_nontemporalAddress_server_data_free(srv_data_ptr);
-        tr_error("Out of memory");
+        tr_error("OOM payload_ptr");
         return -1;
     }
+
     dhcp_client.global_address_cb = error_cb; //TODO Only supporting one instance globaly if we need more for different instances needs code.
     srv_data_ptr->GlobalAddress = true;
     // Build solicit
@@ -214,7 +217,13 @@ int thread_dhcp_client_get_global_address(int8_t interface, uint8_t dhcp_addr[st
 
     // send solicit
     srv_data_ptr->transActionId = dhcp_service_send_req(dhcp_client.service_instance, 0, srv_data_ptr , dhcp_addr, payload_ptr, payload_len, dhcp_solicit_resp_cb);
-    return srv_data_ptr->transActionId ? 0 : -1;
+    if (srv_data_ptr->transActionId == 0) {
+        ns_dyn_mem_free(payload_ptr);
+        libdhcvp6_nontemporalAddress_server_data_free(srv_data_ptr);
+        return -1;
+    }
+
+    return 0;
 }
 
 void thread_dhcp_client_global_address_renew(int8_t interface)

source/libDHCPv6/dhcp_service_api.c

@@ -458,7 +458,7 @@ uint32_t dhcp_service_send_req(uint16_t instance_id, uint8_t options, void *ptr,
     msg_tr_ptr = dhcp_tr_create();
 
     if (msg_tr_ptr == NULL || srv_ptr == NULL || msg_ptr == NULL || receive_resp_cb == NULL || msg_len < 5) {
-        tr_error("request sending failed");
+        tr_error("Request sending failed");
         return 0;
     }