disk/lvm: Don't go beyond the end of the data we read from disk

We unconditionally trusted offset_xl from the LVM label header, even if
it told us that the PV header/disk locations were way off past the end
of the data we read from disk.

Require that the offset be sane, fixing an OOB read and crash.

Fixes: CID 314367, CID 314371
Signed-off-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Patch-Name: 2021-02-security/084-disk-lvm-Don-t-go-beyond-the-end-of-the-data-we-read-from-disk.patch

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index e1299a3486d3171a835c4825219fece114eababa..972b73f4d44e0c8c7322dec1b38a626d848ec908 100644 (file)
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -141,6 +141,20 @@ grub_lvm_detect (grub_disk_t disk,
       goto fail;
     }
 
+  /*
+   * We read a grub_lvm_pv_header and then 2 grub_lvm_disk_locns that
+   * immediately follow the PV header. Make sure we have space for both.
+   */
+  if (grub_le_to_cpu32 (lh->offset_xl) >=
+      GRUB_LVM_LABEL_SIZE - sizeof (struct grub_lvm_pv_header) -
+      2 * sizeof (struct grub_lvm_disk_locn))
+    {
+#ifdef GRUB_UTIL
+      grub_util_info ("LVM PV header/disk locations are beyond the end of the block");
+#endif
+      goto fail;
+    }
+
   pvh = (struct grub_lvm_pv_header *) (buf + grub_le_to_cpu32(lh->offset_xl));
 
   for (i = 0, j = 0; i < GRUB_LVM_ID_LEN; i++)