disk/lvm: GRUB fails to detect LVM volumes due to an incorrect computation of mda_end

When handling a regular LVM volume, GRUB can fail with the message:

  error: disk `lvmid/******-****-****-****-****-****-****/******-****-****-****-****-****-******' not found.

If the condition which triggers this exists, grub-probe will report the
error mentioned above. Similarly, the GRUB boot code will fail to detect
LVM volumes, resulting in a failure to boot off of LVM disks/partitions.
The condition can be created on any LVM VG by an LVM configuration change,
so any system with /boot on LVM can become unbootable at "any" time (after
any LVM configuration change).

The problem is caused by an incorrect computation of mda_end in disk/lvm.c,
when the metadata area wraps around. Apparently, this can start happening at
around 220 metadata changes to the VG.

Fixes: 879c4a834 (lvm: Fix two more potential data-dependent alloc overflows)
Fixes: https://savannah.gnu.org/bugs/?61620

Signed-off-by: Rogier <rogier777@gmail.com>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Tested-By: Michael Chang <mchang@suse.com>

grub-core/disk/lvm.c

@@ -290,7 +290,7 @@ grub_lvm_detect (grub_disk_t disk,
 
   p = q = (char *)ptr;
 
-  if (grub_add ((grub_size_t)metadatabuf, (grub_size_t)mda_size, &ptr))
+  if (grub_add (ptr, (grub_size_t) grub_le_to_cpu64 (rlocn->size), &ptr))
     goto error_parsing_metadata;
 
   mda_end = (char *)ptr;