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>
static int dccp_init_net(struct net *net, u_int16_t proto)
{
	struct dccp_net *dn = dccp_pernet(net);
	struct nf_proto_net *pn = &dn->pn;

	if (!pn->users) {
		/* default values */
		dn->dccp_loose = 1;
		dn->dccp_timeout[CT_DCCP_REQUEST]	= 2 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_RESPOND]	= 4 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_PARTOPEN]	= 4 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_OPEN]		= 12 * 3600 * HZ;
		dn->dccp_timeout[CT_DCCP_CLOSEREQ]	= 64 * HZ;
		dn->dccp_timeout[CT_DCCP_CLOSING]	= 64 * HZ;
		dn->dccp_timeout[CT_DCCP_TIMEWAIT]	= 2 * DCCP_MSL;
	}

	return dccp_kmemdup_sysctl_table(net, pn, dn);
}

static int dccp_init_net(struct net *net, u_int16_t proto)
{
	struct dccp_net *dn = dccp_pernet(net);
	struct nf_proto_net *pn = &dn->pn;

	if (!pn->users) {
		/* default values */
		dn->dccp_loose = 1;
		dn->dccp_timeout[CT_DCCP_REQUEST]	= 2 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_RESPOND]	= 4 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_PARTOPEN]	= 4 * DCCP_MSL;
		dn->dccp_timeout[CT_DCCP_OPEN]		= 12 * 3600 * HZ;
		dn->dccp_timeout[CT_DCCP_CLOSEREQ]	= 64 * HZ;
		dn->dccp_timeout[CT_DCCP_CLOSING]	= 64 * HZ;
		dn->dccp_timeout[CT_DCCP_TIMEWAIT]	= 2 * DCCP_MSL;
	}

	return dccp_kmemdup_sysctl_table(net, pn, dn);
}
