leaseshelper: store server_duid as an allocated string

We either use the value from the environment variable, or learn it from
the existing lease file.

In the second case, the pointer would be pointing into the JSON object
of the first lease with a DUID, owned by leases_array, then
leases_array_new.

Always allocate the string instead, making obvious who should free the
string.

src/network/leaseshelper.c

@@ -122,7 +122,7 @@ main(int argc, char **argv)
     const char *interface = virGetEnvAllowSUID("DNSMASQ_INTERFACE");
     const char *exptime_tmp = virGetEnvAllowSUID("DNSMASQ_LEASE_EXPIRES");
     const char *hostname = virGetEnvAllowSUID("DNSMASQ_SUPPLIED_HOSTNAME");
-    const char *server_duid = virGetEnvAllowSUID("DNSMASQ_SERVER_DUID");
+    char *server_duid = NULL;
     long long currtime = 0;
     long long expirytime = 0;
     size_t i = 0;
@@ -210,6 +210,9 @@ main(int argc, char **argv)
         clientid = argv[2];
     }
 
+    if (VIR_STRDUP(server_duid, virGetEnvAllowSUID("DNSMASQ_SERVER_DUID")) < 0)
+        goto cleanup;
+
     if (virAsprintf(&custom_lease_file,
                     LOCALSTATEDIR "/lib/libvirt/dnsmasq/%s.status",
                     interface) < 0)
@@ -351,11 +354,11 @@ main(int argc, char **argv)
                     /* This is an ipv6 lease */
                     if ((server_duid_tmp
                          = virJSONValueObjectGetString(lease_tmp, "server-duid"))) {
-                        if (!server_duid) {
+                        if (!server_duid && VIR_STRDUP(server_duid, server_duid_tmp) < 0) {
                             /* Control reaches here when the 'action' is not for an
                              * ipv6 lease or, for some weird reason the env var
                              * DNSMASQ_SERVER_DUID wasn't set*/
-                            server_duid = server_duid_tmp;
+                            goto cleanup;
                         }
                     } else {
                         /* Inject server-duid into those ipv6 leases which
@@ -472,6 +475,7 @@ main(int argc, char **argv)
 
     VIR_FREE(pid_file);
     VIR_FREE(exptime);
+    VIR_FREE(server_duid);
     VIR_FREE(lease_entries);
     VIR_FREE(custom_lease_file);
     virJSONValueFree(lease_new);