fs/proc/base.c in the Linux kernel through 3.1 allows local users to obtain sensitive keystroke information via access to /proc/interrupts.
https://vigilance.fr/vulnerability/Linux-kernel-information-disclosure-about-keyboard-11131
https://security-tracker.debian.org/tracker/CVE-2011-4915
https://seclists.org/oss-sec/2011/q4/571
http://people.canonical.com/~ubuntu-security/cve/2011/CVE-2011-4915.html