Function ah_massage_headers

freebsd/netipsec/xform_ah.c:260–525

* Massage IPv4/IPv6 headers for AH processing. */

 * Massage IPv4/IPv6 headers for AH processing.
 */
static int
ah_massage_headers(struct mbuf **m0, int proto, int skip, int alg, int out)
{
	struct mbuf *m = *m0;
	unsigned char *ptr;
	int off, count;

#ifdef INET
	struct ip *ip;
#endif /* INET */

#ifdef INET6
	struct ip6_ext *ip6e;
	struct ip6_hdr ip6;
	int ad, alloc, nxt, noff;
#endif /* INET6 */

	switch (proto) {
#ifdef INET
	case AF_INET:
		/*
		 * This is the least painful way of dealing with IPv4 header
		 * and option processing -- just make sure they're in
		 * contiguous memory.
		 */
		*m0 = m = m_pullup(m, skip);
		if (m == NULL) {
			DPRINTF(("%s: m_pullup failed\n", __func__));
			return ENOBUFS;
		}

		/* Fix the IP header */
		ip = mtod(m, struct ip *);
		if (V_ah_cleartos)
			ip->ip_tos = 0;
		ip->ip_ttl = 0;
		ip->ip_sum = 0;
		ip->ip_off = htons(0);

		ptr = mtod(m, unsigned char *);

		/* IPv4 option processing */
		for (off = sizeof(struct ip); off < skip;) {
			if (ptr[off] == IPOPT_EOL || ptr[off] == IPOPT_NOP ||
			    off + 1 < skip)
				;
			else {
				DPRINTF(("%s: illegal IPv4 option length for "
					"option %d\n", __func__, ptr[off]));

				m_freem(m);
				return EINVAL;
			}

			switch (ptr[off]) {
			case IPOPT_EOL:
				off = skip;  /* End the loop. */
				break;