CVE-2026-98000 to CVE-2026-98999

4 CVEs with public proof-of-concept exploits.

• CVE-2026-982561 PoCsignal: Prevent exec() race
• CVE-2026-9826019 PoCsexec: Cleanup POSIX timers right after de_thread()
• CVE-2026-983851 PoCsched/cache: Decouple sched_cache_group from mm to fix UAF
• CVE-2026-984326 PoCsipv4: free inet_opt and ireq_opt after an RCU grace period