diff options
Diffstat (limited to 'release/src/router/busybox/networking/dnsd.c')
| -rw-r--r-- | release/src/router/busybox/networking/dnsd.c | 518 |
1 files changed, 518 insertions, 0 deletions
diff --git a/release/src/router/busybox/networking/dnsd.c b/release/src/router/busybox/networking/dnsd.c new file mode 100644 index 00000000..56ede3fc --- /dev/null +++ b/release/src/router/busybox/networking/dnsd.c @@ -0,0 +1,518 @@ +/* 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 { + /* can tweak this */ + DEFAULT_TTL = 120, + + /* cannot get bigger packets than 512 per RFC1035. */ + MAX_PACK_LEN = 512, + IP_STRING_LEN = sizeof(".xxx.xxx.xxx.xxx"), + MAX_NAME_LEN = IP_STRING_LEN - 1 + sizeof(".in-addr.arpa"), + REQ_A = 1, + REQ_PTR = 12, +}; + +/* the message from client and first part of response msg */ +struct dns_head { + uint16_t id; + uint16_t flags; + uint16_t nquer; + uint16_t nansw; + uint16_t nauth; + uint16_t nadd; +}; +struct dns_prop { + uint16_t type; + uint16_t class; +}; +/* element of known name, ip address and reversed ip address */ +struct dns_entry { + struct dns_entry *next; + uint32_t ip; + char rip[IP_STRING_LEN]; /* length decimal reversed IP */ + char name[1]; +}; + +#define OPT_verbose (option_mask32) + + +/* + * Insert length of substrings instead of dots + */ +static void undot(char *rip) +{ + int i = 0; + int 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 struct dns_entry *parse_conf_file(const char *fileconf) +{ + char *token[2]; + parser_t *parser; + struct dns_entry *m, *conf_data; + struct dns_entry **nextp; + + conf_data = NULL; + nextp = &conf_data; + + parser = config_open(fileconf); + while (config_read(parser, token, 2, 2, "# \t", PARSE_NORMAL)) { + struct in_addr ip; + uint32_t v32; + + if (inet_aton(token[1], &ip) == 0) { + bb_error_msg("error at line %u, skipping", parser->lineno); + continue; + } + + if (OPT_verbose) + bb_error_msg("name:%s, ip:%s", token[0], token[1]); + + /* sizeof(*m) includes 1 byte for m->name[0] */ + m = xzalloc(sizeof(*m) + strlen(token[0]) + 1); + /*m->next = NULL;*/ + *nextp = m; + nextp = &m->next; + + m->name[0] = '.'; + strcpy(m->name + 1, token[0]); + undot(m->name); + m->ip = ip.s_addr; /* in network order */ + v32 = ntohl(m->ip); + /* inverted order */ + sprintf(m->rip, ".%u.%u.%u.%u", + (uint8_t)(v32), + (uint8_t)(v32 >> 8), + (uint8_t)(v32 >> 16), + (v32 >> 24) + ); + undot(m->rip); + } + config_close(parser); + return conf_data; +} + +/* + * Look query up in dns records and return answer if found. + */ +static char *table_lookup(struct dns_entry *d, + uint16_t type, + char* query_string) +{ + while (d) { + unsigned len = d->name[0]; + /* d->name[len] is the last (non NUL) char */ +#if DEBUG + char *p, *q; + q = query_string + 1; + p = d->name + 1; + fprintf(stderr, "%d/%d p:%s q:%s %d\n", + (int)strlen(p), len, + p, q, (int)strlen(q) + ); +#endif + if (type == htons(REQ_A)) { + /* search by host name */ + if (len != 1 || d->name[1] != '*') { +/* we are lax, hope no name component is ever >64 so that length + * (which will be represented as 'A','B'...) matches a lowercase letter. + * Actually, I think false matches are hard to construct. + * Example. + * [31] len is represented as '1', [65] as 'A', [65+32] as 'a'. + * [65] <65 same chars>[31]<31 same chars>NUL + * [65+32]<65 same chars>1 <31 same chars>NUL + * This example seems to be the minimal case when false match occurs. + */ + if (strcasecmp(d->name, query_string) != 0) + goto next; + } + return (char *)&d->ip; +#if DEBUG + fprintf(stderr, "Found IP:%x\n", (int)d->ip); +#endif + return 0; + } + /* search by IP-address */ + if ((len != 1 || d->name[1] != '*') + /* we assume (do not check) that query_string + * ends in ".in-addr.arpa" */ + && strncmp(d->rip, query_string, strlen(d->rip)) == 0 + ) { +#if DEBUG + fprintf(stderr, "Found name:%s\n", d->name); +#endif + return d->name; + } + next: + d = d->next; + } + + return NULL; +} + +/* + * Decode message and generate answer + */ +/* RFC 1035 +... +Whenever an octet represents a numeric quantity, the left most bit +in the diagram is the high order or most significant bit. +That is, the bit labeled 0 is the most significant bit. +... + +4.1.1. Header section format + 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ID | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + |QR| OPCODE |AA|TC|RD|RA| 0 0 0| RCODE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QDCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ANCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | NSCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | ARCOUNT | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +ID 16 bit random identifier assigned by querying peer. + Used to match query/response. +QR message is a query (0), or a response (1). +OPCODE 0 standard query (QUERY) + 1 inverse query (IQUERY) + 2 server status request (STATUS) +AA Authoritative Answer - this bit is valid in responses. + Responding name server is an authority for the domain name + in question section. Answer section may have multiple owner names + because of aliases. The AA bit corresponds to the name which matches + the query name, or the first owner name in the answer section. +TC TrunCation - this message was truncated. +RD Recursion Desired - this bit may be set in a query and + is copied into the response. If RD is set, it directs + the name server to pursue the query recursively. + Recursive query support is optional. +RA Recursion Available - this be is set or cleared in a + response, and denotes whether recursive query support is + available in the name server. +RCODE Response code. + 0 No error condition + 1 Format error + 2 Server failure - server was unable to process the query + due to a problem with the name server. + 3 Name Error - meaningful only for responses from + an authoritative name server. The referenced domain name + does not exist. + 4 Not Implemented. + 5 Refused. +QDCOUNT number of entries in the question section. +ANCOUNT number of records in the answer section. +NSCOUNT number of records in the authority records section. +ARCOUNT number of records in the additional records section. + +4.1.2. Question section format + +The section contains QDCOUNT (usually 1) entries, each of this format: + 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / QNAME / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QTYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | QCLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +QNAME a domain name represented as a sequence of labels, where + each label consists of a length octet followed by that + number of octets. The domain name terminates with the + zero length octet for the null label of the root. Note + that this field may be an odd number of octets; no + padding is used. +QTYPE a two octet type of the query. + 1 a host address [REQ_A const] + 2 an authoritative name server + 3 a mail destination (Obsolete - use MX) + 4 a mail forwarder (Obsolete - use MX) + 5 the canonical name for an alias + 6 marks the start of a zone of authority + 7 a mailbox domain name (EXPERIMENTAL) + 8 a mail group member (EXPERIMENTAL) + 9 a mail rename domain name (EXPERIMENTAL) + 10 a null RR (EXPERIMENTAL) + 11 a well known service description + 12 a domain name pointer [REQ_PTR const] + 13 host information + 14 mailbox or mail list information + 15 mail exchange + 16 text strings + 0x1c IPv6? + 252 a request for a transfer of an entire zone + 253 a request for mailbox-related records (MB, MG or MR) + 254 a request for mail agent RRs (Obsolete - see MX) + 255 a request for all records +QCLASS a two octet code that specifies the class of the query. + 1 the Internet + (others are historic only) + 255 any class + +4.1.3. Resource record format + +The answer, authority, and additional sections all share the same format: +a variable number of resource records, where the number of records +is specified in the corresponding count field in the header. +Each resource record has this format: + 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + / / + / NAME / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TYPE | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | CLASS | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | TTL | + | | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | RDLENGTH | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--| + / RDATA / + / / + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +NAME a domain name to which this resource record pertains. +TYPE two octets containing one of the RR type codes. This + field specifies the meaning of the data in the RDATA field. +CLASS two octets which specify the class of the data in the RDATA field. +TTL a 32 bit unsigned integer that specifies the time interval + (in seconds) that the record may be cached. +RDLENGTH a 16 bit integer, length in octets of the RDATA field. +RDATA a variable length string of octets that describes the resource. + The format of this information varies according to the TYPE + and CLASS of the resource record. + If the TYPE is A and the CLASS is IN, it's a 4 octet IP address. + +4.1.4. Message compression + +In order to reduce the size of messages, domain names coan be compressed. +An entire domain name or a list of labels at the end of a domain name +is replaced with a pointer to a prior occurance of the same name. + +The pointer takes the form of a two octet sequence: + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ + | 1 1| OFFSET | + +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+ +The first two bits are ones. This allows a pointer to be distinguished +from a label, since the label must begin with two zero bits because +labels are restricted to 63 octets or less. The OFFSET field specifies +an offset from the start of the message (i.e., the first octet +of the ID field in the domain header). +A zero offset specifies the first byte of the ID field, etc. +Domain name in a message can be represented as either: + - a sequence of labels ending in a zero octet + - a pointer + - a sequence of labels ending with a pointer + */ +static int process_packet(struct dns_entry *conf_data, + uint32_t conf_ttl, + uint8_t *buf) +{ + char *answstr; + struct dns_head *head; + struct dns_prop *unaligned_qprop; + char *query_string; + uint8_t *answb; + uint16_t outr_rlen; + uint16_t outr_flags; + uint16_t type; + uint16_t class; + int querystr_len; + + head = (struct dns_head *)buf; + if (head->nquer == 0) { + bb_error_msg("packet has 0 queries, ignored"); + return -1; + } + + if (head->flags & htons(0x8000)) { /* QR bit */ + bb_error_msg("response packet, ignored"); + return -1; + } + + /* start of query string */ + query_string = (void *)(head + 1); + /* caller guarantees strlen is <= MAX_PACK_LEN */ + querystr_len = strlen(query_string) + 1; + /* may be unaligned! */ + unaligned_qprop = (void *)(query_string + querystr_len); + querystr_len += sizeof(unaligned_qprop); + /* where to append answer block */ + answb = (void *)(unaligned_qprop + 1); + + /* QR = 1 "response", RCODE = 4 "Not Implemented" */ + outr_flags = htons(0x8000 | 4); + + move_from_unaligned16(type, &unaligned_qprop->type); + if (type != htons(REQ_A) && type != htons(REQ_PTR)) { + /* we can't handle the query type */ + goto empty_packet; + } + move_from_unaligned16(class, &unaligned_qprop->class); + if (class != htons(1)) { /* not class INET? */ + goto empty_packet; + } + /* OPCODE != 0 "standard query" ? */ + if ((head->flags & htons(0x7800)) != 0) { + goto empty_packet; + } + + /* look up the name */ +#if DEBUG + /* need to convert lengths to dots before we can use it in non-debug */ + bb_info_msg("%s", query_string); +#endif + answstr = table_lookup(conf_data, type, query_string); + outr_rlen = 4; + if (answstr && type == htons(REQ_PTR)) { + /* return a host name */ + outr_rlen = strlen(answstr) + 1; + } + if (!answstr + || (unsigned)(answb - buf) + querystr_len + 4 + 2 + outr_rlen > MAX_PACK_LEN + ) { + /* QR = 1 "response" + * AA = 1 "Authoritative Answer" + * RCODE = 3 "Name Error" */ + outr_flags = htons(0x8000 | 0x0400 | 3); + goto empty_packet; + } + + /* copy query block to answer block */ + memcpy(answb, query_string, querystr_len); + answb += querystr_len; + /* append answer Resource Record */ + move_to_unaligned32((uint32_t *)answb, htonl(conf_ttl)); + answb += 4; + move_to_unaligned32((uint16_t *)answb, htons(outr_rlen)); + answb += 2; + memcpy(answb, answstr, outr_rlen); + answb += outr_rlen; + + /* QR = 1 "response", + * AA = 1 "Authoritative Answer", + * RCODE = 0 "success" */ + outr_flags = htons(0x8000 | 0x0400 | 0); + /* we have one answer */ + head->nansw = htons(1); + + empty_packet: + head->flags |= outr_flags; + head->nauth = head->nadd = 0; + head->nquer = htons(1); // why??? + + return answb - buf; +} + +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"; + const char *fileconf = "/etc/dnsd.conf"; + struct dns_entry *conf_data; + uint32_t conf_ttl = DEFAULT_TTL; + char *sttl, *sport; + len_and_sockaddr *lsa, *from, *to; + unsigned lsa_size; + int udps, opts; + uint16_t port = 53; + uint8_t buf[MAX_PACK_LEN + 1]; + + opts = getopt32(argv, "vi:c:t:p:d", &listen_interface, &fileconf, &sttl, &sport); + //if (opts & 0x1) // -v + //if (opts & 0x2) // -i + //if (opts & 0x4) // -c + if (opts & 0x8) // -t + conf_ttl = xatou_range(sttl, 1, 0xffffffff); + if (opts & 0x10) // -p + port = xatou_range(sport, 1, 0xffff); + if (opts & 0x20) { // -d + bb_daemonize_or_rexec(DAEMON_CLOSE_EXTRA_FDS, argv); + openlog(applet_name, LOG_PID, LOG_DAEMON); + logmode = LOGMODE_SYSLOG; + } + /* Clear all except "verbose" bit */ + option_mask32 &= 1; + + conf_data = parse_conf_file(fileconf); + + 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); + + { + char *p = xmalloc_sockaddr2dotted(&lsa->u.sa); + bb_info_msg("Accepting UDP packets on %s", p); + free(p); + } + + 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("packet size %d, ignored", r); + continue; + } + if (OPT_verbose) + bb_info_msg("Got UDP packet"); + buf[r] = '\0'; /* paranoia */ + r = process_packet(conf_data, conf_ttl, buf); + if (r <= 0) + continue; + send_to_from(udps, buf, r, 0, &from->u.sa, &to->u.sa, lsa->len); + } + return 0; +} |