diff options
Diffstat (limited to 'networking/dnsd.c')
| -rw-r--r-- | networking/dnsd.c | 380 |
1 files changed, 380 insertions, 0 deletions
diff --git a/networking/dnsd.c b/networking/dnsd.c new file mode 100644 index 0000000..e8dcb40 --- /dev/null +++ b/networking/dnsd.c @@ -0,0 +1,380 @@ +/* vi: set sw=4 ts=4: */ +/* + * Mini DNS server implementation for busybox + * + * Copyright (C) 2005 Roberto A. Foglietta (me@roberto.foglietta.name) + * Copyright (C) 2005 Odd Arild Olsen (oao at fibula dot no) + * Copyright (C) 2003 Paul Sheer + * + * Licensed under GPLv2 or later, see file LICENSE in this tarball for details. + * + * Odd Arild Olsen started out with the sheerdns [1] of Paul Sheer and rewrote + * it into a shape which I believe is both easier to understand and maintain. + * I also reused the input buffer for output and removed services he did not + * need. [1] http://threading.2038bug.com/sheerdns/ + * + * Some bugfix and minor changes was applied by Roberto A. Foglietta who made + * the first porting of oao' scdns to busybox also. + */ + +#include "libbb.h" +#include <syslog.h> + +//#define DEBUG 1 +#define DEBUG 0 + +enum { + MAX_HOST_LEN = 16, // longest host name allowed is 15 + IP_STRING_LEN = 18, // .xxx.xxx.xxx.xxx\0 + +//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN + MAX_NAME_LEN = (IP_STRING_LEN + 13), + +/* Cannot get bigger packets than 512 per RFC1035 + In practice this can be set considerably smaller: + Length of response packet is header (12B) + 2*type(4B) + 2*class(4B) + + ttl(4B) + rlen(2B) + r (MAX_NAME_LEN =21B) + + 2*querystring (2 MAX_NAME_LEN= 42B), all together 90 Byte +*/ + MAX_PACK_LEN = 512, + + DEFAULT_TTL = 30, // increase this when not testing? + + REQ_A = 1, + REQ_PTR = 12 +}; + +struct dns_head { // the message from client and first part of response mag + uint16_t id; + uint16_t flags; + uint16_t nquer; // accepts 0 + uint16_t nansw; // 1 in response + uint16_t nauth; // 0 + uint16_t nadd; // 0 +}; +struct dns_prop { + uint16_t type; + uint16_t class; +}; +struct dns_entry { // element of known name, ip address and reversed ip address + struct dns_entry *next; + char ip[IP_STRING_LEN]; // dotted decimal IP + char rip[IP_STRING_LEN]; // length decimal reversed IP + char name[MAX_HOST_LEN]; +}; + +static struct dns_entry *dnsentry; +static uint32_t ttl = DEFAULT_TTL; + +static const char *fileconf = "/etc/dnsd.conf"; + +// Must match getopt32 call +#define OPT_daemon (option_mask32 & 0x10) +#define OPT_verbose (option_mask32 & 0x20) + + +/* + * Convert host name from C-string to dns length/string. + */ +static void convname(char *a, uint8_t *q) +{ + int i = (q[0] == '.') ? 0 : 1; + for (; i < MAX_HOST_LEN-1 && *q; i++, q++) + a[i] = tolower(*q); + a[0] = i - 1; + a[i] = 0; +} + +/* + * Insert length of substrings instead of dots + */ +static void undot(uint8_t * rip) +{ + int i = 0, s = 0; + while (rip[i]) + i++; + for (--i; i >= 0; i--) { + if (rip[i] == '.') { + rip[i] = s; + s = 0; + } else s++; + } +} + +/* + * Read hostname/IP records from file + */ +static void dnsentryinit(void) +{ + char *token[2]; + parser_t *parser; + struct dns_entry *m, *prev; + + prev = dnsentry = NULL; + parser = config_open(fileconf); + while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) { + unsigned a, b, c, d; + /* + * Assumes all host names are lower case only + * Hostnames with more than one label are not handled correctly. + * Presently the dot is copied into name without + * converting to a length/string substring for that label. + */ +// if (!token[1] || sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4) + if (sscanf(token[1], ".%u.%u.%u.%u"+1, &a, &b, &c, &d) != 4) + continue; + + m = xzalloc(sizeof(*m)); + /*m->next = NULL;*/ + sprintf(m->ip, ".%u.%u.%u.%u"+1, a, b, c, d); + sprintf(m->rip, ".%u.%u.%u.%u", d, c, b, a); + undot((uint8_t*)m->rip); + convname(m->name, (uint8_t*)token[0]); + + if (OPT_verbose) + fprintf(stderr, "\tname:%s, ip:%s\n", &(m->name[1]), m->ip); + + if (prev == NULL) + dnsentry = m; + else + prev->next = m; + prev = m; + } + config_close(parser); +} + +/* + * Look query up in dns records and return answer if found + * qs is the query string, first byte the string length + */ +static int table_lookup(uint16_t type, uint8_t * as, uint8_t * qs) +{ + int i; + struct dns_entry *d = dnsentry; + + do { +#if DEBUG + char *p,*q; + q = (char *)&(qs[1]); + p = &(d->name[1]); + fprintf(stderr, "\n%s: %d/%d p:%s q:%s %d", + __FUNCTION__, (int)strlen(p), (int)(d->name[0]), + p, q, (int)strlen(q)); +#endif + if (type == REQ_A) { /* search by host name */ + for (i = 1; i <= (int)(d->name[0]); i++) + if (tolower(qs[i]) != d->name[i]) + break; + if (i > (int)(d->name[0]) || + (d->name[0] == 1 && d->name[1] == '*')) { + strcpy((char *)as, d->ip); +#if DEBUG + fprintf(stderr, " OK as:%s\n", as); +#endif + return 0; + } + } else if (type == REQ_PTR) { /* search by IP-address */ + if ((d->name[0] != 1 || d->name[1] != '*') && + !strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) { + strcpy((char *)as, d->name); + return 0; + } + } + d = d->next; + } while (d); + return -1; +} + +/* + * Decode message and generate answer + */ +static int process_packet(uint8_t *buf) +{ + uint8_t answstr[MAX_NAME_LEN + 1]; + struct dns_head *head; + struct dns_prop *qprop; + uint8_t *from, *answb; + uint16_t outr_rlen; + uint16_t outr_flags; + uint16_t flags; + int lookup_result, type, packet_len; + int querystr_len; + + answstr[0] = '\0'; + + head = (struct dns_head *)buf; + if (head->nquer == 0) { + bb_error_msg("no queries"); + return -1; + } + + if (head->flags & 0x8000) { + bb_error_msg("ignoring response packet"); + return -1; + } + + from = (void *)&head[1]; // start of query string +//FIXME: strlen of untrusted data??! + querystr_len = strlen((char *)from) + 1 + sizeof(struct dns_prop); + answb = from + querystr_len; // where to append answer block + + outr_rlen = 0; + outr_flags = 0; + + qprop = (struct dns_prop *)(answb - 4); + type = ntohs(qprop->type); + + // only let REQ_A and REQ_PTR pass + if (!(type == REQ_A || type == REQ_PTR)) { + goto empty_packet; /* we can't handle the query type */ + } + + if (ntohs(qprop->class) != 1 /* class INET */ ) { + outr_flags = 4; /* not supported */ + goto empty_packet; + } + /* we only support standard queries */ + + if ((ntohs(head->flags) & 0x7800) != 0) + goto empty_packet; + + // We have a standard query + bb_info_msg("%s", (char *)from); + lookup_result = table_lookup(type, answstr, from); + if (lookup_result != 0) { + outr_flags = 3 | 0x0400; // name do not exist and auth + goto empty_packet; + } + if (type == REQ_A) { // return an address + struct in_addr a; // NB! its "struct { unsigned __long__ s_addr; }" + uint32_t v32; + if (!inet_aton((char*)answstr, &a)) { //dotted dec to long conv + outr_flags = 1; /* Frmt err */ + goto empty_packet; + } + v32 = a.s_addr; /* in case long != int */ + memcpy(answstr, &v32, 4); + outr_rlen = 4; // uint32_t IP + } else + outr_rlen = strlen((char *)answstr) + 1; // a host name + outr_flags |= 0x0400; /* authority-bit */ + // we have an answer + head->nansw = htons(1); + + // copy query block to answer block + memcpy(answb, from, querystr_len); + answb += querystr_len; + + // and append answer rr +// FIXME: unaligned accesses?? + *(uint32_t *) answb = htonl(ttl); + answb += 4; + *(uint16_t *) answb = htons(outr_rlen); + answb += 2; + memcpy(answb, answstr, outr_rlen); + answb += outr_rlen; + + empty_packet: + + flags = ntohs(head->flags); + // clear rcode and RA, set responsebit and our new flags + flags |= (outr_flags & 0xff80) | 0x8000; + head->flags = htons(flags); + head->nauth = head->nadd = 0; + head->nquer = htons(1); + + packet_len = answb - buf; + return packet_len; +} + +/* + * Exit on signal + */ +static void interrupt(int sig) +{ + /* unlink("/var/run/dnsd.lock"); */ + bb_error_msg("interrupt, exiting\n"); + kill_myself_with_sig(sig); +} + +int dnsd_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE; +int dnsd_main(int argc UNUSED_PARAM, char **argv) +{ + const char *listen_interface = "0.0.0.0"; + char *sttl, *sport; + len_and_sockaddr *lsa, *from, *to; + unsigned lsa_size; + int udps; + uint16_t port = 53; + /* Paranoid sizing: querystring x2 + ttl + outr_rlen + answstr */ + /* I'd rather see process_packet() fixed instead... */ + uint8_t buf[MAX_PACK_LEN * 2 + 4 + 2 + (MAX_NAME_LEN+1)]; + + getopt32(argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport); + //if (option_mask32 & 0x1) // -i + //if (option_mask32 & 0x2) // -c + if (option_mask32 & 0x4) // -t + ttl = xatou_range(sttl, 1, 0xffffffff); + if (option_mask32 & 0x8) // -p + port = xatou_range(sport, 1, 0xffff); + + if (OPT_verbose) { + bb_info_msg("listen_interface: %s", listen_interface); + bb_info_msg("ttl: %d, port: %d", ttl, port); + bb_info_msg("fileconf: %s", fileconf); + } + + if (OPT_daemon) { + bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv); + openlog(applet_name, LOG_PID, LOG_DAEMON); + logmode = LOGMODE_SYSLOG; + } + + dnsentryinit(); + + signal(SIGINT, interrupt); + bb_signals(0 + /* why? + (1 << SIGPIPE) */ + + (1 << SIGHUP) +#ifdef SIGTSTP + + (1 << SIGTSTP) +#endif +#ifdef SIGURG + + (1 << SIGURG) +#endif + , SIG_IGN); + + lsa = xdotted2sockaddr(listen_interface, port); + udps = xsocket(lsa->u.sa.sa_family, SOCK_DGRAM, 0); + xbind(udps, &lsa->u.sa, lsa->len); + socket_want_pktinfo(udps); /* needed for recv_from_to to work */ + lsa_size = LSA_LEN_SIZE + lsa->len; + from = xzalloc(lsa_size); + to = xzalloc(lsa_size); + + bb_info_msg("Accepting UDP packets on %s", + xmalloc_sockaddr2dotted(&lsa->u.sa)); + + while (1) { + int r; + /* Try to get *DEST* address (to which of our addresses + * this query was directed), and reply from the same address. + * Or else we can exhibit usual UDP ugliness: + * [ip1.multihomed.ip2] <= query to ip1 <= peer + * [ip1.multihomed.ip2] => reply from ip2 => peer (confused) */ + memcpy(to, lsa, lsa_size); + r = recv_from_to(udps, buf, MAX_PACK_LEN + 1, 0, &from->u.sa, &to->u.sa, lsa->len); + if (r < 12 || r > MAX_PACK_LEN) { + bb_error_msg("invalid packet size"); + continue; + } + if (OPT_verbose) + bb_info_msg("Got UDP packet"); + buf[r] = '\0'; /* paranoia */ + r = process_packet(buf); + if (r <= 0) + continue; + send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len); + } + return 0; +} |