Code: static bool dccp_new(struct nf_conn *ct, const struct sk_buff *skb,
		     unsigned int dataoff, unsigned int *timeouts)
{
	struct net *net = nf_ct_net(ct);
	struct dccp_net *dn;
	struct dccp_hdr _dh, *dh;
 	const char *msg;
 	u_int8_t state;
 
	dh = skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);
 	BUG_ON(dh == NULL);
 
 	state = dccp_state_table[CT_DCCP_ROLE_CLIENT][dh->dccph_type][CT_DCCP_NONE];
	switch (state) {
	default:
		dn = dccp_pernet(net);
		if (dn->dccp_loose == 0) {
			msg = "nf_ct_dccp: not picking up existing connection ";
			goto out_invalid;
		}
	case CT_DCCP_REQUEST:
		break;
	case CT_DCCP_INVALID:
		msg = "nf_ct_dccp: invalid state transition ";
		goto out_invalid;
	}

	ct->proto.dccp.role[IP_CT_DIR_ORIGINAL] = CT_DCCP_ROLE_CLIENT;
	ct->proto.dccp.role[IP_CT_DIR_REPLY] = CT_DCCP_ROLE_SERVER;
	ct->proto.dccp.state = CT_DCCP_NONE;
	ct->proto.dccp.last_pkt = DCCP_PKT_REQUEST;
	ct->proto.dccp.last_dir = IP_CT_DIR_ORIGINAL;
	ct->proto.dccp.handshake_seq = 0;
	return true;

out_invalid:
	if (LOG_INVALID(net, IPPROTO_DCCP))
		nf_log_packet(net, nf_ct_l3num(ct), 0, skb, NULL, NULL,
			      NULL, "%s", msg);
	return false;
}

Vulnerability Type: DoS Exec Code 
CWE ID: CWE-20
Summary: net/netfilter/nf_conntrack_proto_dccp.c in the Linux kernel through 3.13.6 uses a DCCP header pointer incorrectly, which allows remote attackers to cause a denial of service (system crash) or possibly execute arbitrary code via a DCCP packet that triggers a call to the (1) dccp_new, (2) dccp_packet, or (3) dccp_error function.
Commit Message: netfilter: nf_conntrack_dccp: fix skb_header_pointer API usages

Some occurences in the netfilter tree use skb_header_pointer() in
the following way ...

  struct dccp_hdr _dh, *dh;
  ...
  skb_header_pointer(skb, dataoff, sizeof(_dh), &dh);

... where dh itself is a pointer that is being passed as the copy
buffer. Instead, we need to use &_dh as the forth argument so that
we're copying the data into an actual buffer that sits on the stack.

Currently, we probably could overwrite memory on the stack (e.g.
with a possibly mal-formed DCCP packet), but unintentionally, as
we only want the buffer to be placed into _dh variable.

Fixes: 2bc780499aa3 ("[NETFILTER]: nf_conntrack: add DCCP protocol support")
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>