mirror of
https://github.com/sheumann/hush.git
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382 lines
9.6 KiB
C
382 lines
9.6 KiB
C
/* vi: set sw=4 ts=4: */
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/*
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* Mini DNS server implementation for busybox
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*
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* Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name)
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* Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no)
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* Copyright (C) 2003 Paul Sheer
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*
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* Licensed under GPLv2 or later, see file LICENSE in this tarball for details.
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*
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* Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote
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* it into a shape which I believe is both easier to understand and maintain.
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* I also reused the input buffer for output and removed services he did not
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* need. [1] http://threading.2038bug.com/sheerdns/
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*
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* Some bugfix and minor changes was applied by Roberto A. Foglietta who made
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* the first porting of oao' scdns to busybox also.
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*/
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#include "libbb.h"
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#include <syslog.h>
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//#define DEBUG 1
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#define DEBUG 0
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enum {
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MAX_HOST_LEN = 16, // longest host name allowed is 15
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IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0
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//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
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MAX_NAME_LEN = (IP_STRING_LEN + 13),
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/* Cannot get bigger packets than 512 per RFC1035
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In practice this can be set considerably smaller:
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Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) +
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ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) +
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2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte
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*/
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MAX_PACK_LEN = 512,
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DEFAULT_TTL = 30, // increase this when not testing?
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REQ_A = 1,
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REQ_PTR = 12
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};
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struct dns_head { // the message from client and first part of response mag
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uint16_t id;
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uint16_t flags;
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uint16_t nquer; // accepts 0
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uint16_t nansw; // 1 in response
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uint16_t nauth; // 0
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uint16_t nadd; // 0
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};
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struct dns_prop {
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uint16_t type;
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uint16_t class;
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};
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struct dns_entry { // element of known name, ip address and reversed ip address
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struct dns_entry *next;
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char ip[IP_STRING_LEN]; // dotted decimal IP
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char rip[IP_STRING_LEN]; // length decimal reversed IP
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char name[MAX_HOST_LEN];
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};
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static struct dns_entry *dnsentry;
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static uint32_t ttl = DEFAULT_TTL;
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static const char *fileconf = "/etc/dnsd.conf";
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// Must match getopt32 call
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#define OPT_daemon (option_mask32 & 0x10)
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#define OPT_verbose (option_mask32 & 0x20)
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/*
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* Convert host name from C-string to dns length/string.
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*/
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static void convname(char *a, uint8_t *q)
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{
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int i = (q[0] == '.') ? 0 : 1;
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for (; i < MAX_HOST_LEN-1 && *q; i++, q++)
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a[i] = tolower(*q);
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a[0] = i - 1;
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a[i] = 0;
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}
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/*
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* Insert length of substrings instead of dots
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*/
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static void undot(uint8_t * rip)
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{
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int i = 0, s = 0;
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while (rip[i])
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i++;
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for (--i; i >= 0; i--) {
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if (rip[i] == '.') {
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rip[i] = s;
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s = 0;
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} else s++;
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}
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}
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/*
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* Read hostname/IP records from file
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*/
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static void dnsentryinit(void)
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{
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parser_t *parser;
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struct dns_entry *m, *prev;
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prev = dnsentry = NULL;
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parser = config_open(fileconf);
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if (parser) {
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char *token[2];
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while (config_read(parser, token, 2, 0, "# \t", 0)) {
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unsigned int a,b,c,d;
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/*
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* Assumes all host names are lower case only
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* Hostnames with more than one label are not handled correctly.
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* Presently the dot is copied into name without
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* converting to a length/string substring for that label.
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*/
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if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4)
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continue;
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m = xzalloc(sizeof(*m));
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/*m->next = NULL;*/
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sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d);
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sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a);
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undot((uint8_t*)m->rip);
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convname(m->name, (uint8_t*)token[0]);
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if (OPT_verbose)
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fprintf(stderr, "\tname:%s, ip:%s\n", &(m->name[1]), m->ip);
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if (prev == NULL)
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dnsentry = m;
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else
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prev->next = m;
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prev = m;
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}
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config_close(parser);
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}
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}
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/*
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* Look query up in dns records and return answer if found
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* qs is the query string, first byte the string length
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*/
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static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs)
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{
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int i;
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struct dns_entry *d = dnsentry;
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do {
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#if DEBUG
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char *p,*q;
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q = (char *)&(qs[1]);
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p = &(d->name[1]);
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fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d",
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__FUNCTION__, (int)strlen(p), (int)(d->name[0]),
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p, q, (int)strlen(q));
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#endif
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if (type == REQ_A) { /* search by host name */
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for (i = 1; i <= (int)(d->name[0]); i++)
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if (tolower(qs[i]) != d->name[i])
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break;
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if (i > (int)(d->name[0]) ||
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(d->name[0] == 1 && d->name[1] == '*')) {
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strcpy((char *)as, d->ip);
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#if DEBUG
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fprintf(stderr, " OK as:%s\n", as);
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#endif
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return 0;
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}
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} else if (type == REQ_PTR) { /* search by IP-address */
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if ((d->name[0] != 1 || d->name[1] != '*') &&
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!strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) {
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strcpy((char *)as, d->name);
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return 0;
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}
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}
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d = d->next;
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} while (d);
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return -1;
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}
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/*
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* Decode message and generate answer
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*/
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static int process_packet(uint8_t *buf)
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{
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uint8_t answstr[MAX_NAME_LEN + 1];
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struct dns_head *head;
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struct dns_prop *qprop;
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uint8_t *from, *answb;
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uint16_t outr_rlen;
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uint16_t outr_flags;
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uint16_t flags;
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int lookup_result, type, packet_len;
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int querystr_len;
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answstr[0] = '\0';
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head = (struct dns_head *)buf;
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if (head->nquer == 0) {
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bb_error_msg("no queries");
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return -1;
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}
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if (head->flags & 0x8000) {
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bb_error_msg("ignoring response packet");
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return -1;
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}
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from = (void *)&head[1]; // start of query string
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//FIXME: strlen of untrusted data??!
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querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop);
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answb = from + querystr_len; // where to append answer block
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outr_rlen = 0;
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outr_flags = 0;
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qprop = (struct dns_prop *)(answb - 4);
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type = ntohs(qprop->type);
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// only let REQ_A and REQ_PTR pass
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if (!(type == REQ_A || type == REQ_PTR)) {
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goto empty_packet; /* we can't handle the query type */
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}
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if (ntohs(qprop->class) != 1 /* class INET */ ) {
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outr_flags = 4; /* not supported */
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goto empty_packet;
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}
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/* we only support standard queries */
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if ((ntohs(head->flags) & 0x7800) != 0)
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goto empty_packet;
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// We have a standard query
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bb_info_msg("%s", (char *)from);
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lookup_result = table_lookup(type, answstr, from);
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if (lookup_result != 0) {
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outr_flags = 3 | 0x0400; // name do not exist and auth
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goto empty_packet;
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}
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if (type == REQ_A) { // return an address
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struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }"
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uint32_t v32;
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if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv
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outr_flags = 1; /* Frmt err */
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goto empty_packet;
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}
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v32 = a.s_addr; /* in case long != int */
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memcpy(answstr, &v32, 4);
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outr_rlen = 4; // uint32_t IP
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} else
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outr_rlen = strlen((char *)answstr) + 1; // a host name
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outr_flags |= 0x0400; /* authority-bit */
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// we have an answer
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head->nansw = htons(1);
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// copy query block to answer block
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memcpy(answb, from, querystr_len);
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answb += querystr_len;
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// and append answer rr
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// FIXME: unaligned accesses??
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*(uint32_t *) answb = htonl(ttl);
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answb += 4;
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*(uint16_t *) answb = htons(outr_rlen);
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answb += 2;
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memcpy(answb, answstr, outr_rlen);
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answb += outr_rlen;
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empty_packet:
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flags = ntohs(head->flags);
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// clear rcode and RA, set responsebit and our new flags
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flags |= (outr_flags & 0xff80) | 0x8000;
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head->flags = htons(flags);
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head->nauth = head->nadd = 0;
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head->nquer = htons(1);
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packet_len = answb - buf;
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return packet_len;
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}
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/*
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* Exit on signal
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*/
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static void interrupt(int sig)
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{
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/* unlink("/var/run/dnsd.lock"); */
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bb_error_msg("interrupt, exiting\n");
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kill_myself_with_sig(sig);
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}
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int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
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int dnsd_main(int argc UNUSED_PARAM, char **argv)
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{
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const char *listen_interface = "0.0.0.0";
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char *sttl, *sport;
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len_and_sockaddr *lsa, *from, *to;
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unsigned lsa_size;
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int udps;
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uint16_t port = 53;
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/* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */
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/* I'd rather see process_packet() fixed instead... */
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uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)];
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getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
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//if (option_mask32 & 0x1) // -i
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//if (option_mask32 & 0x2) // -c
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if (option_mask32 & 0x4) // -t
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ttl = xatou_range(sttl, 1, 0xffffffff);
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if (option_mask32 & 0x8) // -p
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port = xatou_range(sport, 1, 0xffff);
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if (OPT_verbose) {
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bb_info_msg("listen_interface: %s", listen_interface);
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bb_info_msg("ttl: %d, port: %d", ttl, port);
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bb_info_msg("fileconf: %s", fileconf);
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}
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if (OPT_daemon) {
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bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv);
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openlog(applet_name, LOG_PID, LOG_DAEMON);
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logmode = LOGMODE_SYSLOG;
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}
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dnsentryinit();
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signal(SIGINT, interrupt);
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bb_signals(0
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/* why? + (1 << SIGPIPE) */
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+ (1 << SIGHUP)
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#ifdef SIGTSTP
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+ (1 << SIGTSTP)
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#endif
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#ifdef SIGURG
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+ (1 << SIGURG)
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#endif
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, SIG_IGN);
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lsa = xdotted2sockaddr(listen_interface, port);
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udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0);
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xbind(udps, &lsa->u.sa, lsa->len);
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socket_want_pktinfo(udps); /* needed for recv_from_to to work */
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lsa_size = LSA_LEN_SIZE + lsa->len;
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from = xzalloc(lsa_size);
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to = xzalloc(lsa_size);
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bb_info_msg("Accepting UDP packets on %s",
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xmalloc_sockaddr2dotted(&lsa->u.sa));
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while (1) {
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int r;
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/* Try to get *DEST* address (to which of our addresses
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* this query was directed), and reply from the same address.
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* Or else we can exhibit usual UDP ugliness:
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* [ip1.multihomed.ip2] <= query to ip1 <= peer
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* [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */
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memcpy(to, lsa, lsa_size);
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r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len);
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if (r < 12 || r > MAX_PACK_LEN) {
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bb_error_msg("invalid packet size");
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continue;
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}
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if (OPT_verbose)
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bb_info_msg("Got UDP packet");
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buf[r] = '\0'; /* paranoia */
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r = process_packet(buf);
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if (r <= 0)
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continue;
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send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len);
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}
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return 0;
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}
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