Cross-domain signal injection via exec_id overflow

Integer overflow in the Linux kernel before 5.6.5 allows local users to send arbitrary signals to parent processes across security domains. The 32-bit exec_id field in include/linux/sched.h can wrap, defeating do_notify_parent security-domain checks and permitting a child to signal a parent process. Exploitation requires local low-privilege execution and sufficient elapsed time for the counter to overflow; reported consequences include crashing targeted applications, with no demonstrated kernel takeover.