CVE-2026-72418: netfilter: nf_conncount: prevent connlimit drops for early confirmed ct

In the Linux kernel, the following vulnerability has been resolved:

netfilter: nfconncount: prevent connlimit drops for early confirmed ct

Commit 69894e5b4c5e ("netfilter: nftconnlimit: update the count if add was skipped") introduced a regression where packets for valid connections are dropped when using connlimit for soft-limiting scenarios.

The issue occurs when a new connection reuses a socket currently in the TIMEWAIT state. In this scenario, the connection tracking entry is evaluated as already confirmed. Previously, nfconncountadd() assumed that if a connection was confirmed and did not originate from the loopback interface, it should skip the addition and return -EEXIST.

Skipping the addition triggers a garbage collection run that cleans up the TIMEWAIT connection. Consequently, the active connection count drops to 0, which xtconnlimit mishandles, leading to the false rejection of the perfectly valid new connection.

Fix this by replacing the interface check with protocol-agnostic state checks. We now skip the tree insertion and preserve the lockless garbage collection optimization only if the connection is IPSASSURED. This allows early-confirmed setup packets (such as reused TIMEWAIT sockets or locally generated SYN-ACKs) to be properly evaluated and counted without falsely dropping. The goto checkconnections path is maintained to ensure these setup packets are deduplicated correctly.

This has been tested with slowhttptest and HTTP server configured locally to ensure we are not breaking soft-limiting scenarios for local or external connections. In addition, it was tested with a OVS zone limit too.