libxl: Cleanup: Have libxl__alloc_vdev use /libxl

When allocating a vdev for a new disk, look in /libxl/device, rather
than the frontends directory in xenstore.

This is more in line with the other parts of libxl, which ought not to
trust frontends.  In this case, though, there is no security bug prior
to this patch because the frontend is the toolstack domain itself.

If libxl__alloc_vdev were ever changed to take a frontend domain
argument, this patch will fix a latent security bug.

This is a followup to XSA-175.

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

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 9ff08a5ffbe49b79d10c642cbd76ad14aabb7f3d..d5475ed7d8c03eec57939641c881fe3ad01c3bc3 100644 (file)
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -3105,7 +3105,7 @@ static char * libxl__alloc_vdev(libxl__gc *gc, void *get_vdev_user,
 {
     const char *blkdev_start = (const char *) get_vdev_user;
     int devid = 0, disk = 0, part = 0;
-    char *dompath = libxl__xs_get_dompath(gc, LIBXL_TOOLSTACK_DOMID);
+    char *libxl_dom_path = libxl__xs_libxl_path(gc, LIBXL_TOOLSTACK_DOMID);
 
     libxl__device_disk_dev_number(blkdev_start, &disk, &part);
     if (part != 0) {
@@ -3120,7 +3120,7 @@ static char * libxl__alloc_vdev(libxl__gc *gc, void *get_vdev_user,
             return NULL;
         if (libxl__xs_read(gc, t,
                     GCSPRINTF("%s/device/vbd/%d/backend",
-                        dompath, devid)) == NULL) {
+                        libxl_dom_path, devid)) == NULL) {
             if (errno == ENOENT)
                 return libxl__devid_to_vdev(gc, devid);
             else