usb-mtp: add sanity checks on rootdir

Currently, we don't check if rootdir exists and is accessible.
Furthermore, a trailing slash results in a null "desc" string which
ends up in the share not visible in the guest. Add some simple
sanity checks for appropriate permissions. Also, bail out if the
user does not supply an absolute path.

Signed-off-by: Bandan Das <bsd@redhat.com>
Message-id: jpga7bto3on.fsf@linux.bootlegged.copy
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

diff --git a/hw/usb/dev-mtp.c b/hw/usb/dev-mtp.c
index 9846e4b5130be5068273353b7473666c3d1d1a88..7c07295519d33d13fd3755ea7e0ae18a436755ae 100644 (file)
--- a/hw/usb/dev-mtp.c
+++ b/hw/usb/dev-mtp.c
@@ -2038,26 +2038,36 @@ static void usb_mtp_realize(USBDevice *dev, Error **errp)
 {
     MTPState *s = USB_MTP(dev);
 
-    usb_desc_create_serial(dev);
-    usb_desc_init(dev);
-    QTAILQ_INIT(&s->objects);
-    if (s->desc == NULL) {
-        if (s->root == NULL) {
-            error_setg(errp, "usb-mtp: rootdir property must be configured");
-            return;
-        }
-        s->desc = strrchr(s->root, '/');
-        if (s->desc && s->desc[0]) {
-            s->desc = g_strdup(s->desc + 1);
-        } else {
-            s->desc = g_strdup("none");
-        }
+    if ((s->root == NULL) || !g_path_is_absolute(s->root)) {
+        error_setg(errp, "usb-mtp: rootdir must be configured and be an absolute path");
+        return;
     }
+
+    if (access(s->root, R_OK) != 0) {
+        error_setg(errp, "usb-mtp: rootdir does not exist/not readable");
+        return;
+    } else if (!s->readonly && access(s->root, W_OK) != 0) {
+        error_setg(errp, "usb-mtp: rootdir does not have write permissions");
+        return;
+    }
+
     /* Mark store as RW */
     if (!s->readonly) {
         s->flags |= (1 << MTP_FLAG_WRITABLE);
     }
 
+    if (s->desc == NULL) {
+        /*
+         * This does not check if path exists
+         * but we have the checks above
+         */
+        s->desc = g_path_get_basename(s->root);
+    }
+
+    usb_desc_create_serial(dev);
+    usb_desc_init(dev);
+    QTAILQ_INIT(&s->objects);
+
 }
 
 static const VMStateDescription vmstate_usb_mtp = {