From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Daniel Axtens <dja@axtens.net>
Date: Fri, 22 Jan 2021 14:43:58 +1100
Subject: [PATCH] disk/lvm: Sanitize rlocn->offset to prevent wild read

rlocn->offset is read directly from disk and added to the metadatabuf
pointer to create a pointer to a block of metadata. It's a 64-bit
quantity so as long as you don't overflow you can set subsequent
pointers to point anywhere in memory.

Require that rlocn->offset fits within the metadata buffer size.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
---
 grub-core/disk/lvm.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 5fb1b69091c..7356ee83935 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -212,6 +212,14 @@ grub_lvm_detect (grub_disk_t disk,
     }
 
   rlocn = mdah->raw_locns;
+  if (grub_le_to_cpu64 (rlocn->offset) >= grub_le_to_cpu64 (mda_size))
+    {
+#ifdef GRUB_UTIL
+      grub_util_info ("metadata offset is beyond end of metadata area");
+#endif
+      goto fail2;
+    }
+
   if (grub_le_to_cpu64 (rlocn->offset) + grub_le_to_cpu64 (rlocn->size) >
       grub_le_to_cpu64 (mdah->size))
     {