1/*
2 * Copyright (C) 2007 David Malone <dwmalone@FreeBSD.org>
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 *	$FreeBSD$
27 */
28
29#define ACCEPT_FILTER_MOD
30
31#include <sys/param.h>
32#include <sys/kernel.h>
33#include <sys/mbuf.h>
34#include <sys/module.h>
35#include <sys/signalvar.h>
36#include <sys/sysctl.h>
37#include <sys/socketvar.h>
38
39/* check for full DNS request */
40static int sohasdns(struct socket *so, void *arg, int waitflag);
41
42struct packet {
43	struct mbuf *m;		/* Current mbuf. */
44	struct mbuf *n;		/* nextpkt mbuf. */
45	unsigned long moff;	/* Offset of the beginning of m. */
46	unsigned long offset;	/* Which offset we are working at. */
47	unsigned long len;	/* The number of bytes we have to play with. */
48};
49
50#define DNS_OK 0
51#define DNS_WAIT -1
52#define DNS_RUN -2
53
54/* check we can skip over various parts of DNS request */
55static int skippacket(struct sockbuf *sb);
56
57static struct accept_filter accf_dns_filter = {
58	"dnsready",
59	sohasdns,
60	NULL,
61	NULL
62};
63
64static moduledata_t accf_dns_mod = {
65	"accf_dns",
66	accept_filt_generic_mod_event,
67	&accf_dns_filter
68};
69
70DECLARE_MODULE(accf_dns, accf_dns_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
71
72static int
73sohasdns(struct socket *so, void *arg, int waitflag)
74{
75	struct sockbuf *sb = &so->so_rcv;
76
77	/* If the socket is full, we're ready. */
78	if (sb->sb_cc >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
79		goto ready;
80
81	/* Check to see if we have a request. */
82	if (skippacket(sb) == DNS_WAIT)
83		return (SU_OK);
84
85ready:
86	return (SU_ISCONNECTED);
87}
88
89#define GET8(p, val) do { \
90	if (p->offset < p->moff) \
91		return DNS_RUN; \
92	while (p->offset >= p->moff + p->m->m_len) { \
93		p->moff += p->m->m_len; \
94		p->m = p->m->m_next; \
95		if (p->m == NULL) { \
96			p->m = p->n; \
97			p->n = p->m->m_nextpkt; \
98		} \
99		if (p->m == NULL) \
100			return DNS_WAIT; \
101	} \
102	val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
103	p->offset++; \
104	} while (0)
105
106#define GET16(p, val) do { \
107	unsigned int v0, v1; \
108	GET8(p, v0); \
109	GET8(p, v1); \
110	val = v0 * 0x100 + v1; \
111	} while (0)
112
113static int
114skippacket(struct sockbuf *sb) {
115	unsigned long packlen;
116	struct packet q, *p = &q;
117
118	if (sb->sb_cc < 2)
119		return DNS_WAIT;
120
121	q.m = sb->sb_mb;
122	q.n = q.m->m_nextpkt;
123	q.moff = 0;
124	q.offset = 0;
125	q.len = sb->sb_cc;
126
127	GET16(p, packlen);
128	if (packlen + 2 > q.len)
129		return DNS_WAIT;
130
131	return DNS_OK;
132}
133