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 */
40 static int sohasdns(struct socket *so, void *arg, int waitflag);
41
42 ACCEPT_FILTER_DEFINE(accf_dns, "dnsready", sohasdns, NULL, NULL, 1);
43
44 struct 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 */
57 static int skippacket(struct sockbuf *sb);
58
59 static int
sohasdns(struct socket * so,void * arg,int waitflag)60 sohasdns(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
72 ready:
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
100 static int
skippacket(struct sockbuf * sb)101 skippacket(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