Call crextend() before copying old credentials to the new credentials
and replace crcopysafe by crcopy as crcopysafe is is not intended to be
safe in a threaded environment, it drops PROC_LOCK() in while() that
can lead to unexpected results, such as overwrite kernel memory.

In my POV crcopysafe() needs special attention. For now I do not see
any problems with this function, but who knows.

Submitted by: dchagin
Found by: trinity
Security: SA-16:04.linux