(RHSA-2015:2401) Low: grub2 security, bug fix, and enhancement update

The grub2 packages provide version 2 of the Grand Unified Bootloader
(GRUB), a highly configurable and customizable bootloader with modular
architecture. The packages support a variety of kernel formats, file
systems, computer architectures, and hardware devices.

It was discovered that grub2 builds for EFI systems contained modules that
were not suitable to be loaded in a Secure Boot environment. An attacker
could use this flaw to circumvent the Secure Boot mechanisms and load
non-verified code. Attacks could use the boot menu if no password was set,
or the grub2 configuration file if the attacker has root privileges on the
system. (CVE-2015-5281)

This update also fixes the following bugs:

• In one of the earlier updates, GRUB2 was modified to escape forward slash
  (/) characters in several different places. In one of these places, the
  escaping was unnecessary and prevented certain types of kernel command-line
  arguments from being passed to the kernel correctly. With this update,
  GRUB2 no longer escapes the forward slash characters in the mentioned
  place, and the kernel command-line arguments work as expected. (BZ#1125404)

• Previously, GRUB2 relied on a timing mechanism provided by legacy
  hardware, but not by the Hyper-V Gen2 hypervisor, to calibrate its timer
  loop. This prevented GRUB2 from operating correctly on Hyper-V Gen2.
  This update modifies GRUB2 to use a different mechanism on Hyper-V Gen2 to
  calibrate the timing. As a result, Hyper-V Gen2 hypervisors now work as
  expected. (BZ#1150698)

• Prior to this update, users who manually configured GRUB2 to use the
  built-in GNU Privacy Guard (GPG) verification observed the following error
  on boot:

  alloc magic is broken at [addr]: [value] Aborted.

Consequently, the boot failed. The GRUB2 built-in GPG verification has been
modified to no longer free the same memory twice. As a result, the
mentioned error no longer occurs. (BZ#1167977)

• Previously, the system sometimes did not recover after terminating
  unexpectedly and failed to reboot. To fix this problem, the GRUB2 packages
  now enforce file synchronization when creating the GRUB2 configuration
  file, which ensures that the required configuration files are written to
  disk. As a result, the system now reboots successfully after crashing.
  (BZ#1212114)

• Previously, if an unconfigured network driver instance was selected and
  configured when the GRUB2 bootloader was loaded on a different instance,
  GRUB2 did not receive notifications of the Address Resolution Protocol
  (ARP) replies. Consequently, GRUB2 failed with the following error message:

  error: timeout: could not resolve hardware address.

With this update, GRUB2 selects the network driver instance from which it
was loaded. As a result, ARP packets are processed correctly. (BZ#1257475)

In addition, this update adds the following enhancement:

• Sorting of GRUB2 boot menu has been improved. GRUB2 now uses the
  rpmdevtools package to sort available kernels and the configuration file is
  being generated correctly with the most recent kernel version listed at the
  top. (BZ#1124074)

All grub2 users are advised to upgrade to these updated packages, which
contain backported patches to correct these issues and add this
enhancement.