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: releng/12.0/sys/netinet/accf_dns.c 326272 2017-11-27 15:23:17Z pfg $
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 */
42 static int sohasdns(struct socket *so, void *arg, int waitflag);
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 struct accept_filter accf_dns_filter = {
60 "dnsready",
61 sohasdns,
62 NULL,
63 NULL
64 };
65
66 static moduledata_t accf_dns_mod = {
67 "accf_dns",
68 accept_filt_generic_mod_event,
69 &accf_dns_filter
70 };
71
72 DECLARE_MODULE(accf_dns, accf_dns_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE);
73
74 static int
75 sohasdns(struct socket *so, void *arg, int waitflag)
76 {
77 struct sockbuf *sb = &so->so_rcv;
78
79 /* If the socket is full, we're ready. */
80 if (sbused(sb) >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax)
81 goto ready;
82
83 /* Check to see if we have a request. */
84 if (skippacket(sb) == DNS_WAIT)
85 return (SU_OK);
86
87 ready:
88 return (SU_ISCONNECTED);
89 }
90
91 #define GET8(p, val) do { \
92 if (p->offset < p->moff) \
93 return DNS_RUN; \
94 while (p->offset >= p->moff + p->m->m_len) { \
95 p->moff += p->m->m_len; \
96 p->m = p->m->m_next; \
97 if (p->m == NULL) { \
98 p->m = p->n; \
99 p->n = p->m->m_nextpkt; \
100 } \
101 if (p->m == NULL) \
102 return DNS_WAIT; \
103 } \
104 val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \
105 p->offset++; \
106 } while (0)
107
108 #define GET16(p, val) do { \
109 unsigned int v0, v1; \
110 GET8(p, v0); \
111 GET8(p, v1); \
112 val = v0 * 0x100 + v1; \
113 } while (0)
114
115 static int
116 skippacket(struct sockbuf *sb) {
117 unsigned long packlen;
118 struct packet q, *p = &q;
119
120 if (sbavail(sb) < 2)
121 return DNS_WAIT;
122
123 q.m = sb->sb_mb;
124 q.n = q.m->m_nextpkt;
125 q.moff = 0;
126 q.offset = 0;
127 q.len = sbavail(sb);
128
129 GET16(p, packlen);
130 if (packlen + 2 > q.len)
131 return DNS_WAIT;
132
133 return DNS_OK;
134 }
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