Red Hat Bugzilla – Bug 653245
kernel: restrict unprivileged access to kernel syslog [rhel-6.1]
Last modified: 2015-01-04 18:00:04 EST
Description of problem: The kernel syslog contains debugging information that is often useful during exploitation of other vulnerabilities, such as kernel heap addresses. Rather than futilely attempt to sanitize hundreds (or thousands) of printk statements and simultaneously cripple useful debugging functionality, it is far simpler to create an option that prevents unprivileged users from reading the syslog. This patch, loosely based on grsecurity's GRKERNSEC_DMESG, creates the dmesg_restrict sysctl. When set to "0", the default, no restrictions are enforced. When set to "1", only users with CAP_SYS_ADMIN can read the kernel syslog via dmesg(8) or other mechanisms. Upstream commit: http://git.kernel.org/linus/eaf06b241b091357e72b76863ba16e89610d31bd
Patch(es) available on kernel-2.6.32-112.el6
Reproduced in 2.6.32-94.el6.x86_64 and verified in 2.6.32-109.el6.x86_64.
Technical note added. If any revisions are required, please edit the "Technical Notes" field accordingly. All revisions will be proofread by the Engineering Content Services team. New Contents: The kernel syslog contains debugging information that is often useful during exploitation of other vulnerabilities such as kernel heap addresses. With this update, a new CONFIG_SECURITY_DMESG_RESTRICT option has been added to config-generic-rhel which prevents unprivileged users from reading the kernel syslog. This option is by default turned off (0), which means no restrictions.
An advisory has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on therefore solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2011-0542.html