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

[Rarylson Freitas]

More info:

The output of the "problematic" LV is:

$ lvs -o seg_size,vg_extent_size --units s --nosuffix \

> /dev/data/mail


SSize Ext
4294967296 8192

And if I do not specify the LV (output of all LVs):

$ lvs -o seg_size,vg_extent_size --units s --nosuffix
SSize Ext
1949696 8192
3221225472 8192
2147483648 8192
4294967296 8192
4294967296 8192
1050673152 8192
52428800 8192
52428800 8192
2147483648 8192
209715200 8192
10485760 8192
62914560 8192
41943040 8192
83886080 8192
10485760 8192
62914560 8192
1048576000 8192
1048576000 8192
97648640 8192

The problem only occurs when probing our biggest LV.

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

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

Status in grub2 package in Ubuntu:
  New

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.

  Additional info: I discovered that this bug already exists in the GRUB
  upstream (file grub-core/disk/lvm.c, line 466). I will also report
  after this bug for them.

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