The apparmor_setprocattr function in security/apparmor/lsm.c in the Linux kernel before 3.0 does not properly handle invalid parameters, which allows local users to cause a denial of service (NULL pointer dereference and OOPS) or possibly have unspecified other impact by writing to a /proc/#####/attr/current file.
http://ftp.osuosl.org/pub/linux/kernel/v3.0/ChangeLog-3.0
http://www.openwall.com/lists/oss-security/2011/10/17/6
https://github.com/torvalds/linux/commit/a5b2c5b2ad5853591a6cac6134cd0f599a720865