netfilter: nfnetlink_queue: do shared-unconfirmed check before segmentation

Overview

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.

Affected

• Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 79b713ef4261a8ead96af4703f89d0b5f25532e2
• Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 23901aa6b8a2f294c4b774436b4691f3ff863a8f
• Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < b740e7ddd7ca0dbfeafca3f5e52717206cf28524
• Linux >= 7d8dc1c7be8d3509e8f5164dd5df64c8e34d7eeb < 207b3ebacb6113acaaec0d171d5307032c690004
• Linux 6c4a0ba674f410ab99a30a16f32dac0ebfed5cd3
• Linux 6dcc8ba8a6074bb79040f502dc66ad23a58a1c86
• Linux 74e6eb7fd27ef1ccc68041dbc66e6d80d2e4a1a0
• Linux 025b3326c5c409b372d0103ad30f174e55adbd1b
• Linux >= 5.15.166 < 5.16
• Linux >= 6.1.107 < 6.2
• Linux >= 6.6.48 < 6.7
• Linux >= 6.10.7 < 6.11
• Linux 6.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.