[PATCH] lvm: Grub2 fails to detect LVM volumes due to an incorrect computation of mda_end

[Glenn Washburn <development@efficientek.com>]

From: Rogier <rogier777@gmail.com>

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 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>
---
I have done no testing of this patch. I've only created a suitable patch
for review. This seems like a fairly serious issue that might one day bite
me, so I think it deserves a review.

Glenn
---
 grub-core/disk/lvm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 794248540cd3..8535d5a5863a 100644
--- a/grub-core/disk/lvm.c
+++ b/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;
-- 
2.34.1


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