sockets: Fix socket_address_to_string() hostname truncation

We first snprintf() to a fixed buffer, then g_strdup() the result
*boggle*.

Worse, the size of the fixed buffer INET6_ADDRSTRLEN + 5 + 4 is bogus:
the 4 correctly accounts for '[', ']', ':' and '\0', but
INET6_ADDRSTRLEN is not a suitable limit for inet->host, and 5 is not
one for inet->port!  They are for host and port in *numeric* form
(exploiting that INET6_ADDRSTRLEN > INET_ADDRSTRLEN), but inet->host
can also be a hostname, and inet->port can be a service name, to be
resolved with getaddrinfo().

Fortunately, the only user so far is the "socket" network backend's
net_socket_connected(), which uses it to initialize a NetSocketState's
info_str[].  info_str[] has considerable more space: 256 instead of
55.  So the bug's impact appears to be limited to truncated "info
networks" with the "socket" network backend.

The fix is obvious: use g_strdup_printf().
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Message-Id: <1490268208-23368-1-git-send-email-armbru@redhat.com>
Reviewed-by: NPaolo Bonzini <pbonzini@redhat.com>

util/qemu-sockets.c

@@ -1307,19 +1307,14 @@ char *socket_address_to_string(struct SocketAddress *addr, Error **errp)
 {
     char *buf;
     InetSocketAddress *inet;
-    char host_port[INET6_ADDRSTRLEN + 5 + 4];
 
     switch (addr->type) {
     case SOCKET_ADDRESS_KIND_INET:
         inet = addr->u.inet.data;
         if (strchr(inet->host, ':') == NULL) {
-            snprintf(host_port, sizeof(host_port), "%s:%s", inet->host,
-                    inet->port);
-            buf = g_strdup(host_port);
+            buf = g_strdup_printf("%s:%s", inet->host, inet->port);
         } else {
-            snprintf(host_port, sizeof(host_port), "[%s]:%s", inet->host,
-                    inet->port);
-            buf = g_strdup(host_port);
+            buf = g_strdup_printf("[%s]:%s", inet->host, inet->port);
         }
         break;