Function ng_mppc_decompress

freebsd/netgraph/ng_mppc.c:625–836

* Decompress/decrypt packet and put the result in a new mbuf at *resultp. * The original mbuf is not free'd. */

 * The original mbuf is not free'd.
 */
static int
ng_mppc_decompress(node_p node, struct mbuf **datap)
{
	const priv_p priv = NG_NODE_PRIVATE(node);
	struct ng_mppc_dir *const d = &priv->recv;
	u_int16_t header, cc;
	u_int numLost;
	struct mbuf *m = *datap;

	/* We must own the mbuf chain exclusively to modify it. */
	m = m_unshare(m, M_NOWAIT);
	if (m == NULL)
		return (ENOMEM);

	/* Pull off header */
	if (m->m_pkthdr.len < MPPC_HDRLEN) {
		m_freem(m);
		return (EINVAL);
	}
	header = be16dec(mtod(m, void *));
	cc = (header & MPPC_CCOUNT_MASK);
	m_adj(m, MPPC_HDRLEN);

	/* Check for an unexpected jump in the sequence number */
	numLost = ((cc - d->cc) & MPPC_CCOUNT_MASK);

	/* If flushed bit set, we can always handle packet */
	if ((header & MPPC_FLAG_FLUSHED) != 0) {
#ifdef NETGRAPH_MPPC_COMPRESSION
		if (d->history != NULL)
			MPPC_InitDecompressionHistory(d->history);
#endif
#ifdef NETGRAPH_MPPC_ENCRYPTION
		if ((d->cfg.bits & MPPE_BITS) != 0) {
			u_int rekey;

			/* How many times are we going to have to re-key? */
			rekey = ((d->cfg.bits & MPPE_STATELESS) != 0) ?
			    numLost : (numLost / (MPPE_UPDATE_MASK + 1));
			if (rekey > mppe_max_rekey) {
			    if (mppe_block_on_max_rekey) {
				if (mppe_log_max_rekey) {
				    log(LOG_ERR, "%s: too many (%d) packets"
					" dropped, disabling node %p!\n",
					__func__, numLost, node);
				}
				priv->recv.cfg.enable = 0;
				goto failed;
			    } else {
				if (mppe_log_max_rekey) {
				    log(LOG_ERR, "%s: %d packets"
					" dropped, node %p\n",
					__func__, numLost, node);
				}
				goto failed;
			    }
			}