A flaw possibility of race condition and incorrect initialization of the process id was found in the Linux kernel child/parent process identification handling while filtering signal handlers. A local attacker is able to abuse this flaw to bypass checks to send any signal to a privileged process.
https://security.netapp.com/advisory/ntap-20210513-0006/
https://github.com/torvalds/linux/commit/b4e00444cab4c3f3fec876dc0cccc8cbb0d1a948