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.

Reported-by: Ulrich Weber <ulrich.weber@gmail.com>
Fixes: 7d8dc1c7be8d ("netfilter: nf_queue: drop packets with cloned unconfirmed conntracks")
Signed-off-by: Florian Westphal <fw@strlen.de>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/net/netfilter/nf_queue.h b/include/net/netfilter/nf_queue.h
index e6803831d6af..45eb26b2e95b 100644
--- a/include/net/netfilter/nf_queue.h
+++ b/include/net/netfilter/nf_queue.h
@@ -21,6 +21,7 @@ struct nf_queue_entry {
 	struct net_device	*physout;
 #endif
 	struct nf_hook_state	state;
+	bool			nf_ct_is_unconfirmed;
 	u16			size; /* sizeof(entry) + saved route keys */
 	u16			queue_num;