1 /* 2 * Copyright (C) 2007 David Malone <dwmalone@FreeBSD.org> 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 24 * SUCH DAMAGE. 25 * 26 * $FreeBSD$ 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 struct packet { 43 struct mbuf *m; /* Current mbuf. */ 44 struct mbuf *n; /* nextpkt mbuf. */ 45 unsigned long moff; /* Offset of the beginning of m. */ 46 unsigned long offset; /* Which offset we are working at. */ 47 unsigned long len; /* The number of bytes we have to play with. */ 48 }; 49 50 #define DNS_OK 0 51 #define DNS_WAIT -1 52 #define DNS_RUN -2 53 54 /* check we can skip over various parts of DNS request */ 55 static int skippacket(struct sockbuf *sb); 56 57 static struct accept_filter accf_dns_filter = { 58 "dnsready", 59 sohasdns, 60 NULL, 61 NULL 62 }; 63 64 static moduledata_t accf_dns_mod = { 65 "accf_dns", 66 accept_filt_generic_mod_event, 67 &accf_dns_filter 68 }; 69 70 DECLARE_MODULE(accf_dns, accf_dns_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE); 71 72 static int 73 sohasdns(struct socket *so, void *arg, int waitflag) 74 { 75 struct sockbuf *sb = &so->so_rcv; 76 77 /* If the socket is full, we're ready. */ 78 if (sb->sb_cc >= sb->sb_hiwat || sb->sb_mbcnt >= sb->sb_mbmax) 79 goto ready; 80 81 /* Check to see if we have a request. */ 82 if (skippacket(sb) == DNS_WAIT) 83 return (SU_OK); 84 85 ready: 86 return (SU_ISCONNECTED); 87 } 88 89 #define GET8(p, val) do { \ 90 if (p->offset < p->moff) \ 91 return DNS_RUN; \ 92 while (p->offset >= p->moff + p->m->m_len) { \ 93 p->moff += p->m->m_len; \ 94 p->m = p->m->m_next; \ 95 if (p->m == NULL) { \ 96 p->m = p->n; \ 97 p->n = p->m->m_nextpkt; \ 98 } \ 99 if (p->m == NULL) \ 100 return DNS_WAIT; \ 101 } \ 102 val = *(mtod(p->m, unsigned char *) + (p->offset - p->moff)); \ 103 p->offset++; \ 104 } while (0) 105 106 #define GET16(p, val) do { \ 107 unsigned int v0, v1; \ 108 GET8(p, v0); \ 109 GET8(p, v1); \ 110 val = v0 * 0x100 + v1; \ 111 } while (0) 112 113 static int 114 skippacket(struct sockbuf *sb) { 115 unsigned long packlen; 116 struct packet q, *p = &q; 117 118 if (sb->sb_cc < 2) 119 return DNS_WAIT; 120 121 q.m = sb->sb_mb; 122 q.n = q.m->m_nextpkt; 123 q.moff = 0; 124 q.offset = 0; 125 q.len = sb->sb_cc; 126 127 GET16(p, packlen); 128 if (packlen + 2 > q.len) 129 return DNS_WAIT; 130 131 return DNS_OK; 132 } 133