qmp: 'add_client' actually expects sockets

Whether it is SPICE, VNC, D-Bus, or the socket chardev, they all
actually expect a socket kind or will fail in different ways at runtime.

Throw an error early if the given 'add_client' fd is not a socket, and
close it to avoid leaks.

This allows to replace the close() call with a more correct & portable
closesocket() version.

(this will allow importing sockets on Windows with a specialized command
in the following patch, while keeping the remaining monitor associated
sockets/add_client code & usage untouched)

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20230306122751.2355515-6-marcandre.lureau@redhat.com>

monitor/qmp-cmds.c

@@ -14,6 +14,7 @@
  */
 
 #include "qemu/osdep.h"
+#include "qemu/sockets.h"
 #include "monitor-internal.h"
 #include "monitor/qdev.h"
 #include "monitor/qmp-helpers.h"
@@ -139,6 +140,12 @@ void qmp_add_client(const char *protocol, const char *fdname,
         return;
     }
 
+    if (!fd_is_socket(fd)) {
+        error_setg(errp, "parameter @fdname must name a socket");
+        close(fd);
+        return;
+    }
+
     for (i = 0; i < ARRAY_SIZE(protocol_table); i++) {
         if (!strcmp(protocol, protocol_table[i].name)) {
             if (!protocol_table[i].add_client(fd, has_skipauth, skipauth,

qapi/misc.json

@@ -14,6 +14,9 @@
 # Allow client connections for VNC, Spice and socket based
 # character devices to be passed in to QEMU via SCM_RIGHTS.
 #
+# If the FD associated with @fdname is not a socket, the command will fail and
+# the FD will be closed.
+#
 # @protocol: protocol name. Valid names are "vnc", "spice", "@dbus-display" or
 #            the name of a character device (eg. from -chardev id=XXXX)
 #