[bug #45562] grub-probe can't probe large logical volumes (LVM)

[Rarylson Freitas]

URL:
  <http://savannah.gnu.org/bugs/?45562>

                 Summary: grub-probe can't probe large logical volumes (LVM)
                 Project: GNU GRUB
            Submitted by: rarylson
            Submitted on: Thu 16 Jul 2015 02:55:21 PM GMT
                Category: Disk &amp; Partition
                Severity: Major
                Priority: 5 - Normal
              Item Group: Software Error
                  Status: None
                 Privacy: Public
             Assigned to: None
         Originator Name: Rarylson Freitas
        Originator Email: address@hidden
             Open/Closed: Open
         Discussion Lock: Any
                 Release: 
                 Release: Git master
         Reproducibility: Every Time
         Planned Release: None

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Details:

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 was reported at:
https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1475337

However, as I discovered that the same problematic source code exists in the
upstream too, I'm creating this bug report here too.

Talking about the bug:

I 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 (it was created over the current commit
in Git, Master branch - commit ff3c20):

diff --git a/grub-core/disk/lvm.c b/grub-core/disk/lvm.c
index 7b265c7..4a39a5b 100644
--- a/grub-core/disk/lvm.c
+++ b/grub-core/disk/lvm.c
@@ -463,7 +463,8 @@ grub_lvm_detect (grub_disk_t disk,
                    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 only tested this patch in my Ubuntu server using the Debian patched code
(not the upstream code). So, I don't know if it works in the upstream code
too.


I'm attaching this patch too.



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File Attachments:


-------------------------------------------------------
Date: Thu 16 Jul 2015 02:55:21 PM GMT  Name: lvm_big_size_upstream.patch 
Size: 490B   By: rarylson

<http://savannah.gnu.org/bugs/download.php?file_id=34453>

    _______________________________________________________

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