Linux Kernel 6.19.5 and 6.18.15: What the New Netfilter Tweaks Mean for Your PC
The newest point releases bring a small but noticeable tweak to the nf_tables subsystem. If you rely on iptables‑compatible firewalls, the added .abort_skip_removal flag can shave a few milliseconds off rule deletions when a pipapo set backend is in play. This article explains why that matters, how to confirm the kernel is really applied, and what to do if the change triggers an unexpected block.
Why the netfilter change matters
Pablo Neira‑Ayuso’s patch introduces a flag that tells the pipapo set backend to ignore element removal during an abort sequence. In practice, that means the kernel no longer walks a red‑black tree looking for items it will discard anyway; instead it builds a compact array and bails out early. Users who have built custom nftables sets with heavy churn (for example, dynamic blocklists fed by fail2ban) have reported a modest latency drop during mass deletions. The trade‑off is that only pipapo currently uses the shortcut, so other set types continue to follow the old, slower path.
How to verify you’re running a patched kernel
The easiest way to check the version is to open a terminal and type uname -r. A fresh install of 6.19.5 will show “6.19.5‑generic” (or similar) while an upgraded 6.18.15 will display “6.18.15‑lts”. If the output matches one of those strings, the kernel includes the netfilter changes because they were merged into the mainline tree before the release tags. For a deeper dive, grep abort_skip_removal /proc/kallsyms will return an address if the symbol made it into the running image.
Practical steps after upgrading
After flashing the new kernel, reboot and let the system settle for a few minutes before testing firewall rules. A good sanity check is to add a temporary rule that drops traffic from a known IP, then delete it while watching journalctl -f for any nf_tables warnings. If the abort path works as intended, there should be no “failed to remove element” messages. Should an error appear, rolling back to the previous kernel via the GRUB menu is safer than trying to patch the running system.
When to hold back
Not every PC needs the micro‑optimisation that pipapo offers. Home users with static rule sets rarely notice the slowdown, and the extra code path introduces a tiny surface for regressions. If a machine runs a critical service that depends on deterministic firewall behaviour, waiting a couple of weeks until downstream distributions have vetted the change is sensible. In environments where custom nftables scripts are heavily used—think hobbyist IDS setups or container firewalls—the performance gain can be worth the early adoption.
Linux kernel 6.19.5 released
Linux kernel version 6.19.5 is now available:
Full source: https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.19.5.tar.xz
Patch: https://cdn.kernel.org/pub/linux/kernel/v6.x/patch-6.19.5.xz
PGP Signature: https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.19.5.tar.sign
You can view the summary of the changes at the following URL:
https://git.kernel.org/stable/ds/v6.19.5/v6.19.4
Linux kernel 6.18.15 released
Linux kernel version 6.18.15 is now available:
Full source: https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.18.15.tar.xz
Patch: https://cdn.kernel.org/pub/linux/kernel/v6.x/patch-6.18.15.xz
PGP Signature: https://cdn.kernel.org/pub/linux/kernel/v6.x/linux-6.18.15.tar.sign
You can view the summary of the changes at the following URL:
https://git.kernel.org/stable/ds/v6.18.15/v6.18.14
