1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
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
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
42ACCEPT_FILTER_DEFINE(accf_dns, "dnsready", sohasdns, NULL, NULL, 1);
43
44struct packet {
45	struct mbuf *m;		/* Current mbuf. */
46	struct mbuf *n;		/* nextpkt mbuf. */
47	unsigned long moff;	/* Offset of the beginning of m. */
48	unsigned long offset;	/* Which offset we are working at. */
49	unsigned long len;	/* The number of bytes we have to play with. */
50};
51
52#define DNS_OK 0
53#define DNS_WAIT -1
54#define DNS_RUN -2
55
56/* check we can skip over various parts of DNS request */
57static int skippacket(struct sockbuf *sb);
58
59static int
60sohasdns(struct socket *so, void *arg, int waitflag)
61{
62	struct sockbuf *sb = &so->so_rcv;
63
64	/* If the socket is full, we're ready. */
65	if (sbused(sb) >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
66		goto ready;
67
68	/* Check to see if we have a request. */
69	if (skippacket(sb) == DNS_WAIT)
70		return (SU_OK);
71
72ready:
73	return (SU_ISCONNECTED);
74}
75
76#define GET8(p, val) do { \
77	if (p->offset < p->moff) \
78		return DNS_RUN; \
79	while (p->offset >= p->moff + p->m->m_len) { \
80		p->moff += p->m->m_len; \
81		p->m = p->m->m_next; \
82		if (p->m == NULL) { \
83			p->m = p->n; \
84			p->n = p->m->m_nextpkt; \
85		} \
86		if (p->m == NULL) \
87			return DNS_WAIT; \
88	} \
89	val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
90	p->offset++; \
91	} while (0)
92
93#define GET16(p, val) do { \
94	unsigned int v0, v1; \
95	GET8(p, v0); \
96	GET8(p, v1); \
97	val = v0 * 0x100 + v1; \
98	} while (0)
99
100static int
101skippacket(struct sockbuf *sb) {
102	unsigned long packlen;
103	struct packet q, *p = &q;
104
105	if (sbavail(sb) < 2)
106		return DNS_WAIT;
107
108	q.m = sb->sb_mb;
109	q.n = q.m->m_nextpkt;
110	q.moff = 0;
111	q.offset = 0;
112	q.len = sbavail(sb);
113
114	GET16(p, packlen);
115	if (packlen + 2 > q.len)
116		return DNS_WAIT;
117
118	return DNS_OK;
119}
120