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