Function ng_tcpmss_rcvdata

freebsd/netgraph/ng_tcpmss.c:266–357

* Receive data on a hook, and hack MSS. * */

 *
 */
static int
ng_tcpmss_rcvdata(hook_p hook, item_p item)
{
	hpriv_p priv = NG_HOOK_PRIVATE(hook);
	struct mbuf *m = NULL;
	struct ip *ip;
	struct tcphdr *tcp;
	int iphlen, tcphlen, pktlen;
	int pullup_len = 0;
	int error = 0;

	/* Drop packets if filter is not configured on this hook. */
	if (priv->outHook == NULL)
		goto done;

	NGI_GET_M(item, m);

	/* Update stats on incoming hook. */
	pktlen = m->m_pkthdr.len;
	priv->stats.Octets += pktlen;
	priv->stats.Packets++;

	/* Check whether we configured to fix MSS. */
	if (priv->stats.maxMSS == 0)
		goto send;

#define	M_CHECK(length) do {					\
	pullup_len += length;					\
	if ((m)->m_pkthdr.len < pullup_len)			\
		goto send;					\
	if ((m)->m_len < pullup_len &&				\
	   (((m) = m_pullup((m), pullup_len)) == NULL))		\
		ERROUT(ENOBUFS);				\
	} while (0)

	/* Check mbuf packet size and arrange for IP header. */
	M_CHECK(sizeof(struct ip));
	ip = mtod(m, struct ip *);

	/* Check IP version. */
	if (ip->ip_v != IPVERSION)
		ERROUT(EINVAL);

	/* Check IP header length. */
	iphlen = ip->ip_hl << 2;
	if (iphlen < sizeof(struct ip) || iphlen > pktlen )
		ERROUT(EINVAL);

        /* Check if it is TCP. */
	if (!(ip->ip_p == IPPROTO_TCP))
		goto send;

	/* Check mbuf packet size and arrange for IP+TCP header */
	M_CHECK(iphlen - sizeof(struct ip) + sizeof(struct tcphdr));
	ip = mtod(m, struct ip *);
	tcp = (struct tcphdr *)((caddr_t )ip + iphlen);

	/* Check TCP header length. */