libxl: Do not trust backend for vtpm in getinfo (except uuid)

* Do not check the backend for existence.  We have already read the
  /libxl path so know that the vtpm exists (or is supposed to); if the
  backend doesn't exist then that must be the backend's doing.
* Get the frontend path from the /libxl directory.
* The frontend domid is the guest domid, and does not need to be read
  from xenstore (!)

We still attempt to read the uuid from the backend.  This will be
fixed in the next patch.

This is part of XSA-178.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 752dc58ecf64219d0df7765df6739ed61554c46b..223cfb0673277680b39c58943cc090fbdd9ea407 100644 (file)
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -2241,9 +2241,6 @@ int libxl_device_vtpm_getinfo(libxl_ctx *ctx,
     if (!vtpminfo->backend) {
         goto err;
     }
-    if(!libxl__xs_read(gc, XBT_NULL, vtpminfo->backend)) {
-       goto err;
-    }
 
     rc = libxl__backendpath_parse_domid(gc, vtpminfo->backend,
                                         &vtpminfo->backend_id);
@@ -2262,11 +2259,8 @@ int libxl_device_vtpm_getinfo(libxl_ctx *ctx,
     vtpminfo->rref = val ? strtoul(val, NULL, 10) : -1;
 
     vtpminfo->frontend = xs_read(ctx->xsh, XBT_NULL,
-          GCSPRINTF("%s/frontend", vtpminfo->backend), NULL);
-
-    val = libxl__xs_read(gc, XBT_NULL,
-          GCSPRINTF("%s/frontend-id", vtpminfo->backend));
-    vtpminfo->frontend_id = val ? strtoul(val, NULL, 10) : -1;
+          GCSPRINTF("%s/frontend", libxl_path), NULL);
+    vtpminfo->frontend_id = domid;
 
     val = libxl__xs_read(gc, XBT_NULL,
           GCSPRINTF("%s/uuid", vtpminfo->backend));