Fix memory leaks in pioc_w network driver

Fixes a leak in `get_default_device_name()`, if the driver if stopped the memory
holding the device name is never free'd. This could be especially problematic if
the driver is stopped and restarted multiple times, as may be the case with a
battery powered device.

Fixes a potential memory leak of `psk` used for the ap if the given `psk` is
invalid due to not meeting the minimum size requirement.

Signed-off-by: Winford <winford@object.stream>

src/platforms/rp2040/src/lib/networkdriver.c

@@ -39,6 +39,7 @@
 #pragma GCC diagnostic pop
 
 #define PORT_REPLY_SIZE (TUPLE_SIZE(2) + REF_SIZE)
+#define DEFAULT_HOSTNAME_SIZE (strlen("atomvm-") + 12 + 1)
 
 static const char *const ap_atom = ATOM_STR("\x2", "ap");
 static const char *const ap_channel_atom = ATOM_STR("\xA", "ap_channel");
@@ -253,25 +254,22 @@ static term start_sta(term sta_config, GlobalContext *global)
     return OK_ATOM;
 }
 
-static char *get_default_device_name()
+// param should be pointer to malloc'd destination to copy device hostname
+// return ok atom or error as atom
+static term get_default_device_name(char *name)
 {
     uint8_t mac[6];
-    // Device name is used for AP mode. It seems the interface parameter is
-    // ignored and both interfaces have the same MAC address.
+    // Device name is used for AP mode ssid (if undefined), and for the
+    // default dhcp_hostname on both interfaces. It seems the interface
+    // parameter is ignored and both interfaces have the same MAC address.
     int err = cyw43_wifi_get_mac(&cyw43_state, CYW43_ITF_AP, mac);
     if (err) {
-        return NULL;
+        return globalcontext_make_atom(global, ATOM_STR("\x10", "device_mac_error"));
     }
 
-    size_t buf_size = strlen("atomvm-") + 12 + 1;
-    char *buf = malloc(buf_size);
-    if (IS_NULL_PTR(buf)) {
-        return NULL;
-    }
-    snprintf(buf, buf_size,
+    snprintf(name, buf_size,
         "atomvm-%02x%02x%02x%02x%02x%02x", mac[0], mac[1], mac[2], mac[3], mac[4], mac[5]);
-    return buf;
-}
+    return OK_ATOM;
 
 static void network_driver_do_cyw43_assoc(GlobalContext *glb)
 {
@@ -390,7 +388,15 @@ static term start_ap(term ap_config, GlobalContext *global)
     //
     char *ssid = NULL;
     if (term_is_invalid_term(ssid_term)) {
-        ssid = get_default_device_name();
+        ssid = malloc(DEFAULT_HOSTNAME_SIZE);
+        if (IS_NULL_PTR(ssid)) {
+            return OUT_OF_MEMORY_ATOM;
+        }
+        term error = get_default_device_name(ssid);
+        if (error != OK_ATOM) {
+            free(ssid);
+            return error;
+        }
     } else {
         int ok = 0;
         ssid = interop_term_to_string(ssid_term, &ok);
@@ -404,6 +410,7 @@ static term start_ap(term ap_config, GlobalContext *global)
         psk = interop_term_to_string(pass_term, &ok);
         if (strlen(psk) < 8) {
             free(ssid);
+            free(psk);
             return BADARG_ATOM;
         }
         if (!ok) {