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