| 1 | /* vi: set sw=4 ts=4: */
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| 2 | /*
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| 3 | * Mini DNS server implementation for busybox
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| 4 | *
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| 5 | * Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name)
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| 6 | * Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no)
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| 7 | * Copyright (C) 2003 Paul Sheer
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| 8 | *
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| 9 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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| 10 | *
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| 11 | * Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote
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| 12 | * it into a shape which I believe is both easier to understand and maintain.
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| 13 | * I also reused the input buffer for output and removed services he did not
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| 14 | * need. [1] http://threading.2038bug.com/sheerdns/
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| 15 | *
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| 16 | * Some bugfix and minor changes was applied by Roberto A. Foglietta who made
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| 17 | * the first porting of oao' scdns to busybox also.
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| 18 | */
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| 19 |
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| 20 | //usage:#define dnsd_trivial_usage
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| 21 | //usage: "[-dvs] [-c CONFFILE] [-t TTL_SEC] [-p PORT] [-i ADDR]"
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| 22 | //usage:#define dnsd_full_usage "\n\n"
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| 23 | //usage: "Small static DNS server daemon\n"
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| 24 | //usage: "\n -c FILE Config file"
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| 25 | //usage: "\n -t SEC TTL"
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| 26 | //usage: "\n -p PORT Listen on PORT"
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| 27 | //usage: "\n -i ADDR Listen on ADDR"
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| 28 | //usage: "\n -d Daemonize"
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| 29 | //usage: "\n -v Verbose"
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| 30 | //usage: "\n -s Send successful replies only. Use this if you want"
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| 31 | //usage: "\n to use /etc/resolv.conf with two nameserver lines:"
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| 32 | //usage: "\n nameserver DNSD_SERVER"
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| 33 | //usage: "\n nameserver NORMAL_DNS_SERVER"
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| 34 |
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| 35 | #include "libbb.h"
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| 36 | #include <syslog.h>
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| 37 |
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| 38 | //#define DEBUG 1
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| 39 | #define DEBUG 0
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| 40 |
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| 41 | enum {
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| 42 | /* can tweak this */
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| 43 | DEFAULT_TTL = 120,
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| 44 |
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| 45 | /* cannot get bigger packets than 512 per RFC1035. */
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| 46 | MAX_PACK_LEN = 512,
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| 47 | IP_STRING_LEN = sizeof(".xxx.xxx.xxx.xxx"),
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| 48 | MAX_NAME_LEN = IP_STRING_LEN - 1 + sizeof(".in-addr.arpa"),
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| 49 | REQ_A = 1,
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| 50 | REQ_PTR = 12,
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| 51 | };
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| 52 |
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| 53 | /* the message from client and first part of response msg */
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| 54 | struct dns_head {
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| 55 | uint16_t id;
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| 56 | uint16_t flags;
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| 57 | uint16_t nquer;
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| 58 | uint16_t nansw;
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| 59 | uint16_t nauth;
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| 60 | uint16_t nadd;
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| 61 | };
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| 62 | /* Structure used to access type and class fields.
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| 63 | * They are totally unaligned, but gcc 4.3.4 thinks that pointer of type uint16_t*
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| 64 | * is 16-bit aligned and replaces 16-bit memcpy (in move_from_unaligned16 macro)
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| 65 | * with aligned halfword access on arm920t!
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| 66 | * Oh well. Slapping PACKED everywhere seems to help: */
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| 67 | struct type_and_class {
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| 68 | uint16_t type PACKED;
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| 69 | uint16_t class PACKED;
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| 70 | } PACKED;
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| 71 | /* element of known name, ip address and reversed ip address */
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| 72 | struct dns_entry {
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| 73 | struct dns_entry *next;
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| 74 | uint32_t ip;
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| 75 | char rip[IP_STRING_LEN]; /* length decimal reversed IP */
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| 76 | char name[1];
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| 77 | };
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| 78 |
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| 79 | #define OPT_verbose (option_mask32 & 1)
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| 80 | #define OPT_silent (option_mask32 & 2)
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| 81 |
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| 82 |
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| 83 | /*
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| 84 | * Insert length of substrings instead of dots
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| 85 | */
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| 86 | static void undot(char *rip)
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| 87 | {
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| 88 | int i = 0;
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| 89 | int s = 0;
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| 90 |
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| 91 | while (rip[i])
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| 92 | i++;
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| 93 | for (--i; i >= 0; i--) {
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| 94 | if (rip[i] == '.') {
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| 95 | rip[i] = s;
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| 96 | s = 0;
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| 97 | } else {
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| 98 | s++;
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| 99 | }
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| 100 | }
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| 101 | }
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| 102 |
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| 103 | /*
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| 104 | * Read hostname/IP records from file
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| 105 | */
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| 106 | static struct dns_entry *parse_conf_file(const char *fileconf)
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| 107 | {
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| 108 | char *token[2];
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| 109 | parser_t *parser;
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| 110 | struct dns_entry *m, *conf_data;
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| 111 | struct dns_entry **nextp;
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| 112 |
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| 113 | conf_data = NULL;
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| 114 | nextp = &conf_data;
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| 115 |
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| 116 | parser = config_open(fileconf);
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| 117 | while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) {
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| 118 | struct in_addr ip;
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| 119 | uint32_t v32;
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| 120 |
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| 121 | if (inet_aton(token[1], &ip) == 0) {
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| 122 | bb_error_msg("error at line %u, skipping", parser->lineno);
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| 123 | continue;
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| 124 | }
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| 125 |
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| 126 | if (OPT_verbose)
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| 127 | bb_error_msg("name:%s, ip:%s", token[0], token[1]);
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| 128 |
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| 129 | /* sizeof(*m) includes 1 byte for m->name[0] */
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| 130 | m = xzalloc(sizeof(*m) + strlen(token[0]) + 1);
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| 131 | /*m->next = NULL;*/
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| 132 | *nextp = m;
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| 133 | nextp = &m->next;
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| 134 |
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| 135 | m->name[0] = '.';
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| 136 | strcpy(m->name + 1, token[0]);
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| 137 | undot(m->name);
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| 138 | m->ip = ip.s_addr; /* in network order */
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| 139 | v32 = ntohl(m->ip);
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| 140 | /* inverted order */
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| 141 | sprintf(m->rip, ".%u.%u.%u.%u",
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| 142 | (uint8_t)(v32),
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| 143 | (uint8_t)(v32 >> 8),
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| 144 | (uint8_t)(v32 >> 16),
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| 145 | (v32 >> 24)
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| 146 | );
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| 147 | undot(m->rip);
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| 148 | }
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| 149 | config_close(parser);
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| 150 | return conf_data;
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| 151 | }
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| 152 |
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| 153 | /*
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| 154 | * Look query up in dns records and return answer if found.
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| 155 | */
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| 156 | static char *table_lookup(struct dns_entry *d,
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| 157 | uint16_t type,
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| 158 | char* query_string)
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| 159 | {
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| 160 | while (d) {
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| 161 | unsigned len = d->name[0];
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| 162 | /* d->name[len] is the last (non NUL) char */
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| 163 | #if DEBUG
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| 164 | char *p, *q;
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| 165 | q = query_string + 1;
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| 166 | p = d->name + 1;
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| 167 | fprintf(stderr, "%d/%d p:%s q:%s %d\n",
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| 168 | (int)strlen(p), len,
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| 169 | p, q, (int)strlen(q)
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| 170 | );
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| 171 | #endif
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| 172 | if (type == htons(REQ_A)) {
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| 173 | /* search by host name */
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| 174 | if (len != 1 || d->name[1] != '*') {
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| 175 | /* we are lax, hope no name component is ever >64 so that length
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| 176 | * (which will be represented as 'A','B'...) matches a lowercase letter.
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| 177 | * Actually, I think false matches are hard to construct.
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| 178 | * Example.
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| 179 | * [31] len is represented as '1', [65] as 'A', [65+32] as 'a'.
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| 180 | * [65] <65 same chars>[31]<31 same chars>NUL
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| 181 | * [65+32]<65 same chars>1 <31 same chars>NUL
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| 182 | * This example seems to be the minimal case when false match occurs.
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| 183 | */
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| 184 | if (strcasecmp(d->name, query_string) != 0)
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| 185 | goto next;
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| 186 | }
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| 187 | return (char *)&d->ip;
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| 188 | #if DEBUG
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| 189 | fprintf(stderr, "Found IP:%x\n", (int)d->ip);
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| 190 | #endif
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| 191 | return 0;
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| 192 | }
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| 193 | /* search by IP-address */
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| 194 | if ((len != 1 || d->name[1] != '*')
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| 195 | /* we assume (do not check) that query_string
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| 196 | * ends in ".in-addr.arpa" */
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| 197 | && strncmp(d->rip, query_string, strlen(d->rip)) == 0
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| 198 | ) {
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| 199 | #if DEBUG
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| 200 | fprintf(stderr, "Found name:%s\n", d->name);
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| 201 | #endif
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| 202 | return d->name;
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| 203 | }
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| 204 | next:
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| 205 | d = d->next;
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| 206 | }
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| 207 |
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| 208 | return NULL;
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| 209 | }
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| 210 |
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| 211 | /*
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| 212 | * Decode message and generate answer
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| 213 | */
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| 214 | /* RFC 1035
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| 215 | ...
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| 216 | Whenever an octet represents a numeric quantity, the left most bit
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| 217 | in the diagram is the high order or most significant bit.
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| 218 | That is, the bit labeled 0 is the most significant bit.
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| 219 | ...
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| 220 |
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| 221 | 4.1.1. Header section format
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| 222 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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| 223 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 224 | | ID |
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| 225 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 226 | |QR| OPCODE |AA|TC|RD|RA| 0 0 0| RCODE |
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| 227 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 228 | | QDCOUNT |
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| 229 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 230 | | ANCOUNT |
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| 231 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 232 | | NSCOUNT |
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| 233 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 234 | | ARCOUNT |
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| 235 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 236 | ID 16 bit random identifier assigned by querying peer.
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| 237 | Used to match query/response.
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| 238 | QR message is a query (0), or a response (1).
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| 239 | OPCODE 0 standard query (QUERY)
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| 240 | 1 inverse query (IQUERY)
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| 241 | 2 server status request (STATUS)
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| 242 | AA Authoritative Answer - this bit is valid in responses.
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| 243 | Responding name server is an authority for the domain name
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| 244 | in question section. Answer section may have multiple owner names
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| 245 | because of aliases. The AA bit corresponds to the name which matches
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| 246 | the query name, or the first owner name in the answer section.
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| 247 | TC TrunCation - this message was truncated.
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| 248 | RD Recursion Desired - this bit may be set in a query and
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| 249 | is copied into the response. If RD is set, it directs
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| 250 | the name server to pursue the query recursively.
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| 251 | Recursive query support is optional.
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| 252 | RA Recursion Available - this be is set or cleared in a
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| 253 | response, and denotes whether recursive query support is
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| 254 | available in the name server.
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| 255 | RCODE Response code.
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| 256 | 0 No error condition
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| 257 | 1 Format error
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| 258 | 2 Server failure - server was unable to process the query
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| 259 | due to a problem with the name server.
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| 260 | 3 Name Error - meaningful only for responses from
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| 261 | an authoritative name server. The referenced domain name
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| 262 | does not exist.
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| 263 | 4 Not Implemented.
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| 264 | 5 Refused.
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| 265 | QDCOUNT number of entries in the question section.
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| 266 | ANCOUNT number of records in the answer section.
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| 267 | NSCOUNT number of records in the authority records section.
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| 268 | ARCOUNT number of records in the additional records section.
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| 269 |
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| 270 | 4.1.2. Question section format
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| 271 |
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| 272 | The section contains QDCOUNT (usually 1) entries, each of this format:
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| 273 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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| 274 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 275 | / QNAME /
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| 276 | / /
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| 277 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 278 | | QTYPE |
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| 279 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 280 | | QCLASS |
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| 281 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 282 | QNAME a domain name represented as a sequence of labels, where
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| 283 | each label consists of a length octet followed by that
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| 284 | number of octets. The domain name terminates with the
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| 285 | zero length octet for the null label of the root. Note
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| 286 | that this field may be an odd number of octets; no
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| 287 | padding is used.
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| 288 | QTYPE a two octet type of the query.
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| 289 | 1 a host address [REQ_A const]
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| 290 | 2 an authoritative name server
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| 291 | 3 a mail destination (Obsolete - use MX)
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| 292 | 4 a mail forwarder (Obsolete - use MX)
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| 293 | 5 the canonical name for an alias
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| 294 | 6 marks the start of a zone of authority
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| 295 | 7 a mailbox domain name (EXPERIMENTAL)
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| 296 | 8 a mail group member (EXPERIMENTAL)
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| 297 | 9 a mail rename domain name (EXPERIMENTAL)
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| 298 | 10 a null RR (EXPERIMENTAL)
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| 299 | 11 a well known service description
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| 300 | 12 a domain name pointer [REQ_PTR const]
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| 301 | 13 host information
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| 302 | 14 mailbox or mail list information
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| 303 | 15 mail exchange
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| 304 | 16 text strings
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| 305 | 0x1c IPv6?
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| 306 | 252 a request for a transfer of an entire zone
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| 307 | 253 a request for mailbox-related records (MB, MG or MR)
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| 308 | 254 a request for mail agent RRs (Obsolete - see MX)
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| 309 | 255 a request for all records
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| 310 | QCLASS a two octet code that specifies the class of the query.
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| 311 | 1 the Internet
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| 312 | (others are historic only)
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| 313 | 255 any class
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| 314 |
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| 315 | 4.1.3. Resource Record format
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| 316 |
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| 317 | The answer, authority, and additional sections all share the same format:
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| 318 | a variable number of resource records, where the number of records
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| 319 | is specified in the corresponding count field in the header.
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| 320 | Each resource record has this format:
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| 321 | 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
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| 322 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 323 | / /
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| 324 | / NAME /
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| 325 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 326 | | TYPE |
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| 327 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 328 | | CLASS |
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| 329 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 330 | | TTL |
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| 331 | | |
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| 332 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 333 | | RDLENGTH |
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| 334 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--|
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| 335 | / RDATA /
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| 336 | / /
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| 337 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 338 | NAME a domain name to which this resource record pertains.
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| 339 | TYPE two octets containing one of the RR type codes. This
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| 340 | field specifies the meaning of the data in the RDATA field.
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| 341 | CLASS two octets which specify the class of the data in the RDATA field.
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| 342 | TTL a 32 bit unsigned integer that specifies the time interval
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| 343 | (in seconds) that the record may be cached.
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| 344 | RDLENGTH a 16 bit integer, length in octets of the RDATA field.
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| 345 | RDATA a variable length string of octets that describes the resource.
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| 346 | The format of this information varies according to the TYPE
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| 347 | and CLASS of the resource record.
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| 348 | If the TYPE is A and the CLASS is IN, it's a 4 octet IP address.
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| 349 |
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| 350 | 4.1.4. Message compression
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| 351 |
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| 352 | In order to reduce the size of messages, domain names coan be compressed.
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| 353 | An entire domain name or a list of labels at the end of a domain name
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| 354 | is replaced with a pointer to a prior occurance of the same name.
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| 355 |
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| 356 | The pointer takes the form of a two octet sequence:
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| 357 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 358 | | 1 1| OFFSET |
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| 359 | +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| 360 | The first two bits are ones. This allows a pointer to be distinguished
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| 361 | from a label, since the label must begin with two zero bits because
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| 362 | labels are restricted to 63 octets or less. The OFFSET field specifies
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| 363 | an offset from the start of the message (i.e., the first octet
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| 364 | of the ID field in the domain header).
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| 365 | A zero offset specifies the first byte of the ID field, etc.
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| 366 | Domain name in a message can be represented as either:
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| 367 | - a sequence of labels ending in a zero octet
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| 368 | - a pointer
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| 369 | - a sequence of labels ending with a pointer
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| 370 | */
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| 371 | static int process_packet(struct dns_entry *conf_data,
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| 372 | uint32_t conf_ttl,
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| 373 | uint8_t *buf)
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| 374 | {
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| 375 | struct dns_head *head;
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| 376 | struct type_and_class *unaligned_type_class;
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| 377 | const char *err_msg;
|
|---|
| 378 | char *query_string;
|
|---|
| 379 | char *answstr;
|
|---|
| 380 | uint8_t *answb;
|
|---|
| 381 | uint16_t outr_rlen;
|
|---|
| 382 | uint16_t outr_flags;
|
|---|
| 383 | uint16_t type;
|
|---|
| 384 | uint16_t class;
|
|---|
| 385 | int query_len;
|
|---|
| 386 |
|
|---|
| 387 | head = (struct dns_head *)buf;
|
|---|
| 388 | if (head->nquer == 0) {
|
|---|
| 389 | bb_error_msg("packet has 0 queries, ignored");
|
|---|
| 390 | return 0; /* don't reply */
|
|---|
| 391 | }
|
|---|
| 392 | if (head->flags & htons(0x8000)) { /* QR bit */
|
|---|
| 393 | bb_error_msg("response packet, ignored");
|
|---|
| 394 | return 0; /* don't reply */
|
|---|
| 395 | }
|
|---|
| 396 | /* QR = 1 "response", RCODE = 4 "Not Implemented" */
|
|---|
| 397 | outr_flags = htons(0x8000 | 4);
|
|---|
| 398 | err_msg = NULL;
|
|---|
| 399 |
|
|---|
| 400 | /* start of query string */
|
|---|
| 401 | query_string = (void *)(head + 1);
|
|---|
| 402 | /* caller guarantees strlen is <= MAX_PACK_LEN */
|
|---|
| 403 | query_len = strlen(query_string) + 1;
|
|---|
| 404 | /* may be unaligned! */
|
|---|
| 405 | unaligned_type_class = (void *)(query_string + query_len);
|
|---|
| 406 | query_len += sizeof(*unaligned_type_class);
|
|---|
| 407 | /* where to append answer block */
|
|---|
| 408 | answb = (void *)(unaligned_type_class + 1);
|
|---|
| 409 |
|
|---|
| 410 | /* OPCODE != 0 "standard query"? */
|
|---|
| 411 | if ((head->flags & htons(0x7800)) != 0) {
|
|---|
| 412 | err_msg = "opcode != 0";
|
|---|
| 413 | goto empty_packet;
|
|---|
| 414 | }
|
|---|
| 415 | move_from_unaligned16(class, &unaligned_type_class->class);
|
|---|
| 416 | if (class != htons(1)) { /* not class INET? */
|
|---|
| 417 | err_msg = "class != 1";
|
|---|
| 418 | goto empty_packet;
|
|---|
| 419 | }
|
|---|
| 420 | move_from_unaligned16(type, &unaligned_type_class->type);
|
|---|
| 421 | if (type != htons(REQ_A) && type != htons(REQ_PTR)) {
|
|---|
| 422 | /* we can't handle this query type */
|
|---|
| 423 | //TODO: happens all the time with REQ_AAAA (0x1c) requests - implement those?
|
|---|
| 424 | err_msg = "type is !REQ_A and !REQ_PTR";
|
|---|
| 425 | goto empty_packet;
|
|---|
| 426 | }
|
|---|
| 427 |
|
|---|
| 428 | /* look up the name */
|
|---|
| 429 | answstr = table_lookup(conf_data, type, query_string);
|
|---|
| 430 | #if DEBUG
|
|---|
| 431 | /* Shows lengths instead of dots, unusable for !DEBUG */
|
|---|
| 432 | bb_error_msg("'%s'->'%s'", query_string, answstr);
|
|---|
| 433 | #endif
|
|---|
| 434 | outr_rlen = 4;
|
|---|
| 435 | if (answstr && type == htons(REQ_PTR)) {
|
|---|
| 436 | /* returning a host name */
|
|---|
| 437 | outr_rlen = strlen(answstr) + 1;
|
|---|
| 438 | }
|
|---|
| 439 | if (!answstr
|
|---|
| 440 | || (unsigned)(answb - buf) + query_len + 4 + 2 + outr_rlen > MAX_PACK_LEN
|
|---|
| 441 | ) {
|
|---|
| 442 | /* QR = 1 "response"
|
|---|
| 443 | * AA = 1 "Authoritative Answer"
|
|---|
| 444 | * RCODE = 3 "Name Error" */
|
|---|
| 445 | err_msg = "name is not found";
|
|---|
| 446 | outr_flags = htons(0x8000 | 0x0400 | 3);
|
|---|
| 447 | goto empty_packet;
|
|---|
| 448 | }
|
|---|
| 449 |
|
|---|
| 450 | /* Append answer Resource Record */
|
|---|
| 451 | memcpy(answb, query_string, query_len); /* name, type, class */
|
|---|
| 452 | answb += query_len;
|
|---|
| 453 | move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl));
|
|---|
| 454 | answb += 4;
|
|---|
| 455 | move_to_unaligned16((uint16_t *)answb, htons(outr_rlen));
|
|---|
| 456 | answb += 2;
|
|---|
| 457 | memcpy(answb, answstr, outr_rlen);
|
|---|
| 458 | answb += outr_rlen;
|
|---|
| 459 |
|
|---|
| 460 | /* QR = 1 "response",
|
|---|
| 461 | * AA = 1 "Authoritative Answer",
|
|---|
| 462 | * TODO: need to set RA bit 0x80? One user says nslookup complains
|
|---|
| 463 | * "Got recursion not available from SERVER, trying next server"
|
|---|
| 464 | * "** server can't find HOSTNAME"
|
|---|
| 465 | * RCODE = 0 "success"
|
|---|
| 466 | */
|
|---|
| 467 | if (OPT_verbose)
|
|---|
| 468 | bb_error_msg("returning positive reply");
|
|---|
| 469 | outr_flags = htons(0x8000 | 0x0400 | 0);
|
|---|
| 470 | /* we have one answer */
|
|---|
| 471 | head->nansw = htons(1);
|
|---|
| 472 |
|
|---|
| 473 | empty_packet:
|
|---|
| 474 | if ((outr_flags & htons(0xf)) != 0) { /* not a positive response */
|
|---|
| 475 | if (OPT_verbose) {
|
|---|
| 476 | bb_error_msg("%s, %s",
|
|---|
| 477 | err_msg,
|
|---|
| 478 | OPT_silent ? "dropping query" : "sending error reply"
|
|---|
| 479 | );
|
|---|
| 480 | }
|
|---|
| 481 | if (OPT_silent)
|
|---|
| 482 | return 0;
|
|---|
| 483 | }
|
|---|
| 484 | head->flags |= outr_flags;
|
|---|
| 485 | head->nauth = head->nadd = 0;
|
|---|
| 486 | head->nquer = htons(1); // why???
|
|---|
| 487 |
|
|---|
| 488 | return answb - buf;
|
|---|
| 489 | }
|
|---|
| 490 |
|
|---|
| 491 | int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
|
|---|
| 492 | int dnsd_main(int argc UNUSED_PARAM, char **argv)
|
|---|
| 493 | {
|
|---|
| 494 | const char *listen_interface = "0.0.0.0";
|
|---|
| 495 | const char *fileconf = "/etc/dnsd.conf";
|
|---|
| 496 | struct dns_entry *conf_data;
|
|---|
| 497 | uint32_t conf_ttl = DEFAULT_TTL;
|
|---|
| 498 | char *sttl, *sport;
|
|---|
| 499 | len_and_sockaddr *lsa, *from, *to;
|
|---|
| 500 | unsigned lsa_size;
|
|---|
| 501 | int udps, opts;
|
|---|
| 502 | uint16_t port = 53;
|
|---|
| 503 | /* Ensure buf is 32bit aligned (we need 16bit, but 32bit can't hurt) */
|
|---|
| 504 | uint8_t buf[MAX_PACK_LEN + 1] ALIGN4;
|
|---|
| 505 |
|
|---|
| 506 | opts = getopt32(argv, "vsi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport);
|
|---|
| 507 | //if (opts & (1 << 0)) // -v
|
|---|
| 508 | //if (opts & (1 << 1)) // -s
|
|---|
| 509 | //if (opts & (1 << 2)) // -i
|
|---|
| 510 | //if (opts & (1 << 3)) // -c
|
|---|
| 511 | if (opts & (1 << 4)) // -t
|
|---|
| 512 | conf_ttl = xatou_range(sttl, 1, 0xffffffff);
|
|---|
| 513 | if (opts & (1 << 5)) // -p
|
|---|
| 514 | port = xatou_range(sport, 1, 0xffff);
|
|---|
| 515 | if (opts & (1 << 6)) { // -d
|
|---|
| 516 | bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
|
|---|
| 517 | openlog(applet_name, LOG_PID, LOG_DAEMON);
|
|---|
| 518 | logmode = LOGMODE_SYSLOG;
|
|---|
| 519 | }
|
|---|
| 520 |
|
|---|
| 521 | conf_data = parse_conf_file(fileconf);
|
|---|
| 522 |
|
|---|
| 523 | lsa = xdotted2sockaddr(listen_interface, port);
|
|---|
| 524 | udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
|
|---|
| 525 | xbind(udps, &lsa->u.sa, lsa->len);
|
|---|
| 526 | socket_want_pktinfo(udps); /* needed for recv_from_to to work */
|
|---|
| 527 | lsa_size = LSA_LEN_SIZE + lsa->len;
|
|---|
| 528 | from = xzalloc(lsa_size);
|
|---|
| 529 | to = xzalloc(lsa_size);
|
|---|
| 530 |
|
|---|
| 531 | {
|
|---|
| 532 | char *p = xmalloc_sockaddr2dotted(&lsa->u.sa);
|
|---|
| 533 | bb_error_msg("accepting UDP packets on %s", p);
|
|---|
| 534 | free(p);
|
|---|
| 535 | }
|
|---|
| 536 |
|
|---|
| 537 | while (1) {
|
|---|
| 538 | int r;
|
|---|
| 539 | /* Try to get *DEST* address (to which of our addresses
|
|---|
| 540 | * this query was directed), and reply from the same address.
|
|---|
| 541 | * Or else we can exhibit usual UDP ugliness:
|
|---|
| 542 | * [ip1.multihomed.ip2] <= query to ip1 <= peer
|
|---|
| 543 | * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
|
|---|
| 544 | memcpy(to, lsa, lsa_size);
|
|---|
| 545 | r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
|
|---|
| 546 | if (r < 12 || r > MAX_PACK_LEN) {
|
|---|
| 547 | bb_error_msg("packet size %d, ignored", r);
|
|---|
| 548 | continue;
|
|---|
| 549 | }
|
|---|
| 550 | if (OPT_verbose)
|
|---|
| 551 | bb_error_msg("got UDP packet");
|
|---|
| 552 | buf[r] = '\0'; /* paranoia */
|
|---|
| 553 | r = process_packet(conf_data, conf_ttl, buf);
|
|---|
| 554 | if (r <= 0)
|
|---|
| 555 | continue;
|
|---|
| 556 | send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len);
|
|---|
| 557 | }
|
|---|
| 558 | return 0;
|
|---|
| 559 | }
|
|---|
