[Bug 1475337] Re: grub-probe can't probe large logical volumes (LVM)

[Steve Langasek]

The Precise Pangolin has reached end of life, so this bug will not be
fixed for that release

** Changed in: grub2 (Ubuntu Precise)
       Status: Confirmed => Won't Fix

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https://bugs.launchpad.net/bugs/1475337

Title:
  grub-probe can't probe large logical volumes (LVM)

Status in grub:
  Unknown
Status in grub2 package in Ubuntu:
  Fix Released
Status in grub2 source package in Precise:
  Won't Fix

Bug description:
  Hi,

  I've had a problem when using the `grub-probe` binary to probe large
  LVM partitions (for example, a 1.5 TB partition).

  This problem was discovered/tested in an Ubuntu 12.04.5.

  When trying to probe these large LVM partitions, we get erros like:

      $ grub-probe -vvv /PATH/TO/MY/LVM
      [...]
      grub-core/kern/disk.c:494: Read out of range: sector 0x0 (out of disk).
      [...]
      grub-probe: error: unknown filesystem.

  This bug seems like this one:
  https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1027363

  So, a debug the problem and I discovered that the problem occurs due
  to an inappropriate multiplication in the file grub-core/disk/lvm.c:

      lv->size += seg->extent_count * vg->extent_size;

  The lv->size var is an unsigned 64-bits integer. However, the next two
  vars are respectively an unsigned int and an int. As the result of
  (unsigned int) * (int) is an integer, it's very easy to get a
  multiplication overflow (in my case, the result of the multiplication
  was zero -> lv->size = 0, resulting in the "out of disk" error).

  So, I'm proposing a patch for this bug (file lvm_big_size.patch, to be
  applied after all Debian patched):

      Index: grub2-1.99/grub-core/disk/lvm.c
      ===================================================================
      --- grub2-1.99.orig/grub-core/disk/lvm.c	2011-04-18 21:16:16.000000000 +0000
      +++ grub2-1.99/grub-core/disk/lvm.c	2015-07-16 03:05:41.624035502 +0000
       -629,7 +629,8 @@
             goto lvs_segment_fail;
           p += sizeof("type = \"") - 1;

      -		  lv->size += seg->extent_count * vg->extent_size;
      +		  lv->size += ((grub_uint64_t) seg->extent_count
      +				* (grub_uint64_t) vg->extent_size);

           if (grub_memcmp (p, "striped\"",
              sizeof ("striped\"") - 1) == 0)

  I have already tested this patch using the following commands and it
  worked:

      quilt push -a
      DEB_BUILD_OPTIONS=nocheck fakeroot debian/rules build/grub-coreboot

  I'm attaching this patch.

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