Here is a new improved patch for verifying user access to string
passed in to kernel on write to /proc/irq/<pid>/smp_affinity.

The access_ok() but missing __get_user() on each byte earlier patch
has been replaced with a copy_from_user().

I have built it and verified that it handles write requests
as before, on an ia64 system (well - you can no longer pass
more than 14 spaces after the 'R' - tough).