A local attacker using FreeBSD4. 3 design vulnerabilities to obtain system privilege-vulnerability warning-the black bar safety net

Found FreeBSD 4.3 there is a design on the vulnerability, which allows the user in the other processes inserted in the signal handlers to. The problem is in the rforkRFPROC|RFSIGSHARE, if the child process exec a setuid program, then the parent process set up a signal handlers, the signal handler...