[RFT] nf_contrack_udp: handle packets with padding and hwchecksum
flat view
From: Stephen Hemminger <hidden>
Date: 2012-02-17 18:16:48
Also in:
netfilter-devel
If UDP packet with extra padding is received on a device that does hardware checksumming (but not checking) is processed by netfilter conntrack, it would generate a bogus warning about the checksum being incorrect. There were two possible solutions. The netfilter conntrack code could trim the packet, discarding the extra padding and adjusting the checksum. Or it can force regular non-offloaded checksum. This patch implements the latter on the principal that is better for firewall code to not modify the packet. Compile tested only; haven't been able to reproduce the problem yet. Signed-off-by: Stephen Hemminger <redacted> --- Patch against -net tree, after review/test it should go to stable as well.
--- a/net/netfilter/nf_conntrack_proto_udp.c 2012-01-10 10:57:00.407196614 -0800
+++ b/net/netfilter/nf_conntrack_proto_udp.c 2012-02-17 10:06:18.038472559 -0800@@ -125,12 +125,17 @@ static int udp_error(struct net *net, st * We skip checking packets on the outgoing path * because the checksum is assumed to be correct. * FIXME: Source route IP option packets --RR */ - if (net->ct.sysctl_checksum && hooknum == NF_INET_PRE_ROUTING && - nf_checksum(skb, hooknum, dataoff, IPPROTO_UDP, pf)) { - if (LOG_INVALID(net, IPPROTO_UDP)) - nf_log_packet(pf, 0, skb, NULL, NULL, NULL, - "nf_ct_udp: bad UDP checksum "); - return -NF_ACCEPT; + if (net->ct.sysctl_checksum && hooknum == NF_INET_PRE_ROUTING) { + /* Special case for hardware checksum offload with padding */ + if (skb->ip_summed == CHECKSUM_COMPLETE && udplen > ntohs(hdr->len)) + skb->ip_summed = CHECKSUM_NONE; + + if (nf_checksum(skb, hooknum, dataoff, IPPROTO_UDP, pf)) { + if (LOG_INVALID(net, IPPROTO_UDP)) + nf_log_packet(pf, 0, skb, NULL, NULL, NULL, + "nf_ct_udp: bad UDP checksum "); + return -NF_ACCEPT; + } } return NF_ACCEPT;