2.6 - RHSA-2015:2401

Problem Description:

Updated grub2 packages that fix one security issue, several bugs, and add one enhancement are now available for Red Hat Enterprise Linux 7.

Red Hat Product Security has rated this update as having Low security impact. A Common Vulnerability Scoring System (CVSS) base score, which gives a detailed severity rating, is available from the CVE link in the References section.

2. Relevant releases/architectures:

Red Hat Enterprise Linux Client (v. 7) - x86_64 Red Hat Enterprise Linux Client Optional (v. 7) - x86_64 Red Hat Enterprise Linux ComputeNode (v. 7) - x86_64 Red Hat Enterprise Linux ComputeNode Optional (v. 7) - x86_64 Red Hat Enterprise Linux Server (v. 7) - aarch64, ppc64, ppc64le, x86_64 Red Hat Enterprise Linux Server Optional (v. 7) - aarch64, x86_64 Red Hat Enterprise Linux Workstation (v. 7) - x86_64 Red Hat Enterprise Linux Workstation Optional (v. 7) - x86_64

3. Description:

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.

4. Solution:

Before applying this update, make sure all previously released errata relevant to your system have been applied.

For details on how to apply this update, refer to:

https://access.redhat.com/articles/11258

5. Bugs fixed (https://bugzilla.redhat.com/):

1001279 - grub2 can't boot new xfs CRC-capable disk format 1124074 - grub2-mkconfig wrong sorting 1125404 - [RHEL 7] grub2 improperly escapes spaces in kernel parameters 1148650 - no docs explaining what config path GRUB expects when netbooting 1177003 - yum reinstall kernel causes duplicate entry in grub menu 1211101 - grub2 fw_path variable is incorrect for x86 EFI network boot: too many path components stripped 1264103 - CVE-2015-5281 grub2: modules built in on EFI builds that allow loading arbitrary code, circumventing secure boot