[Bug 1511108] [NEW] Handle odd buffer lengths in checksum

[Linn Crosetto]

Public bug reported:

Buffers of odd length can be passed to the checksum, for example
signatures. This results in reading 1 byte beyond the buffer and can
produce an incorrect checksum if the extra byte is non-zero.

Attaching a patch changing csum_bytes() to prevent overflowing the
buffer, while taking the extra byte into account if the length is odd.
Tested with a UEFI binary containing an odd-length signature, and also
detach/attach on a binary signed with Microsoft signtool.

** Affects: sbsigntool (Ubuntu)
     Importance: Undecided
         Status: New

** Patch added: "0001-Handle-odd-buffer-lengths-in-checksum.patch"
   https://bugs.launchpad.net/bugs/1511108/+attachment/4507901/+files/0001-Handle-odd-buffer-lengths-in-checksum.patch

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https://bugs.launchpad.net/bugs/1511108

Title:
  Handle odd buffer lengths in checksum

Status in sbsigntool package in Ubuntu:
  New

Bug description:
  Buffers of odd length can be passed to the checksum, for example
  signatures. This results in reading 1 byte beyond the buffer and can
  produce an incorrect checksum if the extra byte is non-zero.

  Attaching a patch changing csum_bytes() to prevent overflowing the
  buffer, while taking the extra byte into account if the length is odd.
  Tested with a UEFI binary containing an odd-length signature, and also
  detach/attach on a binary signed with Microsoft signtool.

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