loopback: Do not automaticaly replace existing loopback dev, error instead

If there is a loopback device with the same name as the one to be created,
instead of closing the old one and replacing it with the new one, return an
error instead. If the loopback device was created, its probably being used
by something and just replacing it may cause GRUB to crash unexpectedly.
This fixes obvious problems like "loopback d (d)/somefile". Its not too
onerous to force the user to delete the loopback first with the "-d" switch.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

diff --git a/grub-core/disk/loopback.c b/grub-core/disk/loopback.c
index cdf9123fa57456a971f131788f3a3b0d34fc62be..41bebd14fe37f1e706e0030f64ffca9420a197e6 100644 (file)
--- a/grub-core/disk/loopback.c
+++ b/grub-core/disk/loopback.c
@@ -92,24 +92,16 @@ grub_cmd_loopback (grub_extcmd_context_t ctxt, int argc, char **args)
   if (argc < 2)
     return grub_error (GRUB_ERR_BAD_ARGUMENT, N_("filename expected"));
 
+  /* Check that a device with requested name does not already exist. */
+  for (newdev = loopback_list; newdev; newdev = newdev->next)
+    if (grub_strcmp (newdev->devname, args[0]) == 0)
+      return grub_error (GRUB_ERR_BAD_ARGUMENT, "device name already exists");
+
   file = grub_file_open (args[1], GRUB_FILE_TYPE_LOOPBACK
                         | GRUB_FILE_TYPE_NO_DECOMPRESS);
   if (! file)
     return grub_errno;
 
-  /* First try to replace the old device.  */
-  for (newdev = loopback_list; newdev; newdev = newdev->next)
-    if (grub_strcmp (newdev->devname, args[0]) == 0)
-      break;
-
-  if (newdev)
-    {
-      grub_file_close (newdev->file);
-      newdev->file = file;
-
-      return 0;
-    }
-
   /* Unable to replace it, make a new entry.  */
   newdev = grub_malloc (sizeof (struct grub_loopback));
   if (! newdev)