From 5bed9f3f63f8f9d2b1758c24640cbf77b5377511 Mon Sep 17 00:00:00 2001 From: Kevin Mitchell Date: Fri, 14 Jan 2022 20:00:50 -0800 Subject: [PATCH] netfilter: conntrack: mark UDP zero checksum as CHECKSUM_UNNECESSARY The udp_error function verifies the checksum of incoming UDP packets if one is set. This has the desirable side effect of setting skb->ip_summed to CHECKSUM_COMPLETE, signalling that this verification need not be repeated further up the stack. Conversely, when the UDP checksum is empty, which is perfectly legal (at least inside IPv4), udp_error previously left no trace that the checksum had been deemed acceptable. This was a problem in particular for nf_reject_ipv4, which verifies the checksum in nf_send_unreach() before sending ICMP_DEST_UNREACH. It makes no accommodation for zero UDP checksums unless they are already marked as CHECKSUM_UNNECESSARY. This commit ensures packets with empty UDP checksum are marked as CHECKSUM_UNNECESSARY, which is explicitly recommended in skbuff.h. Signed-off-by: Kevin Mitchell Acked-by: Florian Westphal Signed-off-by: Pablo Neira Ayuso --- net/netfilter/nf_conntrack_proto_udp.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nf_conntrack_proto_udp.c b/net/netfilter/nf_conntrack_proto_udp.c index 3b516cffc779b..12f793d8fe0cb 100644 --- a/net/netfilter/nf_conntrack_proto_udp.c +++ b/net/netfilter/nf_conntrack_proto_udp.c @@ -63,8 +63,10 @@ static bool udp_error(struct sk_buff *skb, } /* Packet with no checksum */ - if (!hdr->check) + if (!hdr->check) { + skb->ip_summed = CHECKSUM_UNNECESSARY; return false; + } /* Checksum invalid? Ignore. * We skip checking packets on the outgoing path