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 * $FreeBSD$ 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 */ 42 static int sohasdns(struct socket *so, void *arg, int waitflag); 43 44 ACCEPT_FILTER_DEFINE(accf_dns, "dnsready", sohasdns, NULL, NULL, 1); 45 46 struct 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 */ 59 static int skippacket(struct sockbuf *sb); 60 61 static int 62 sohasdns(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 74 ready: 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) 101 102 static int 103 skippacket(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