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netfilter: conntrack: validate SCTP crc32c in PREROUTING

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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>
This commit is contained in:
Davide Caratti 2017-01-02 13:29:41 +01:00 committed by Pablo Neira Ayuso
parent 300ae14946
commit cf6e007eef
1 changed files with 32 additions and 0 deletions
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32
net/netfilter/nf_conntrack_proto_sctp.c
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@ -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,