CVE-2026-45859

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

netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

Ulrich reports a regression with nfqueue:

If an application did not set the 'F_GSO' capability flag and a gso

packet with an unconfirmed nf_conn entry is received all packets are

now dropped instead of queued, because the check happens after

skb_gso_segment(). In that case, we did have exclusive ownership

of the skb and its associated conntrack entry. The elevated use

count is due to skb_clone happening via skb_gso_segment().

Move the check so that its peformed vs. the aggregated packet.

Then, annotate the individual segments except the first one so we

can do a 2nd check at reinject time.

For the normal case, where userspace does in-order reinjects, this avoids

packet drops: first reinjected segment continues traversal and confirms

entry, remaining segments observe the confirmed entry.

While at it, simplify nf_ct_drop_unconfirmed(): We only care about

unconfirmed entries with a refcnt > 1, there is no need to special-case

dying entries.

This only happens with UDP. With TCP, the only unconfirmed packet will

be the TCP SYN, those aren't aggregated by GRO.

Next patch adds a udpgro test case to cover this scenario.