netfilter: conntrack: validate SCTP crc32c in PREROUTING

implement sctp_error to let nf_conntrack_in validate crc32c on the packet
transport header. Assign skb->ip_summed to CHECKSUM_UNNECESSARY and return
NF_ACCEPT in case of successful validation; otherwise, return -NF_ACCEPT to
let netfilter skip connection tracking, like other protocols do.

Besides preventing corrupted packets from matching conntrack entries, this
fixes functionality of REJECT target: it was not generating any ICMP upon
reception of SCTP packets, because it was computing RFC 1624 checksum on
the packet and systematically mismatching crc32c in the SCTP header.

Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

diff --git a/net/netfilter/nf_conntrack_proto_sctp.c b/net/netfilter/nf_conntrack_proto_sctp.c
index a0efde38da44742ccab5578f5d726afbf5758f41..44a647418948444842195564b3700524b6eaedd5 100644 (file)
--- a/net/netfilter/nf_conntrack_proto_sctp.c
+++ b/net/netfilter/nf_conntrack_proto_sctp.c
@@ -22,7 +22,9 @@
 #include <linux/seq_file.h>
 #include <linux/spinlock.h>
 #include <linux/interrupt.h>
+#include <net/sctp/checksum.h>
 
+#include <net/netfilter/nf_log.h>
 #include <net/netfilter/nf_conntrack.h>
 #include <net/netfilter/nf_conntrack_l4proto.h>
 #include <net/netfilter/nf_conntrack_ecache.h>
@@ -505,6 +507,34 @@ static bool sctp_new(struct nf_conn *ct, const struct sk_buff *skb,
        return true;
 }
 
+static int sctp_error(struct net *net, struct nf_conn *tpl, struct sk_buff *skb,
+                     unsigned int dataoff, enum ip_conntrack_info *ctinfo,
+                     u8 pf, unsigned int hooknum)
+{
+       const struct sctphdr *sh;
+       struct sctphdr _sctph;
+       const char *logmsg;
+
+       sh = skb_header_pointer(skb, dataoff, sizeof(_sctph), &_sctph);
+       if (!sh) {
+               logmsg = "nf_ct_sctp: short packet ";
+               goto out_invalid;
+       }
+       if (net->ct.sysctl_checksum && hooknum == NF_INET_PRE_ROUTING &&
+           skb->ip_summed == CHECKSUM_NONE) {
+               if (sh->checksum != sctp_compute_cksum(skb, dataoff)) {
+                       logmsg = "nf_ct_sctp: bad CRC ";
+                       goto out_invalid;
+               }
+               skb->ip_summed = CHECKSUM_UNNECESSARY;
+       }
+       return NF_ACCEPT;
+out_invalid:
+       if (LOG_INVALID(net, IPPROTO_SCTP))
+               nf_log_packet(net, pf, 0, skb, NULL, NULL, NULL, "%s", logmsg);
+       return -NF_ACCEPT;
+}
+
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
 
 #include <linux/netfilter/nfnetlink.h>
@@ -752,6 +782,7 @@ struct nf_conntrack_l4proto nf_conntrack_l4proto_sctp4 __read_mostly = {
        .packet                 = sctp_packet,
        .get_timeouts           = sctp_get_timeouts,
        .new                    = sctp_new,
+       .error                  = sctp_error,
        .me                     = THIS_MODULE,
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
        .to_nlattr              = sctp_to_nlattr,
@@ -786,6 +817,7 @@ struct nf_conntrack_l4proto nf_conntrack_l4proto_sctp6 __read_mostly = {
        .packet                 = sctp_packet,
        .get_timeouts           = sctp_get_timeouts,
        .new                    = sctp_new,
+       .error                  = sctp_error,
        .me                     = THIS_MODULE,
 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
        .to_nlattr              = sctp_to_nlattr,