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Diffstat (limited to 'src/lib/krb5/os/dnssrv.c')
-rw-r--r-- | src/lib/krb5/os/dnssrv.c | 273 |
1 files changed, 273 insertions, 0 deletions
diff --git a/src/lib/krb5/os/dnssrv.c b/src/lib/krb5/os/dnssrv.c new file mode 100644 index 0000000..90279fd --- /dev/null +++ b/src/lib/krb5/os/dnssrv.c @@ -0,0 +1,273 @@ +/* + * lib/krb5/os/dnssrv.c + * + * Copyright 1990,2000,2001,2002,2003 by the Massachusetts Institute of Technology. + * All Rights Reserved. + * + * Export of this software from the United States of America may + * require a specific license from the United States Government. + * It is the responsibility of any person or organization contemplating + * export to obtain such a license before exporting. + * + * WITHIN THAT CONSTRAINT, permission to use, copy, modify, and + * distribute this software and its documentation for any purpose and + * without fee is hereby granted, provided that the above copyright + * notice appear in all copies and that both that copyright notice and + * this permission notice appear in supporting documentation, and that + * the name of M.I.T. not be used in advertising or publicity pertaining + * to distribution of the software without specific, written prior + * permission. Furthermore if you modify this software you must label + * your software as modified software and not distribute it in such a + * fashion that it might be confused with the original M.I.T. software. + * M.I.T. makes no representations about the suitability of + * this software for any purpose. It is provided "as is" without express + * or implied warranty. + * + * + * do DNS SRV RR queries + */ + +#ifdef KRB5_DNS_LOOKUP +#define NEED_SOCKETS +#include "k5-int.h" +#include "os-proto.h" +#include <stdio.h> +#ifdef WSHELPER +#include <wshelper.h> +#else /* WSHELPER */ +#include <arpa/inet.h> +#include <arpa/nameser.h> +#include <resolv.h> +#include <netdb.h> +#endif /* WSHELPER */ +#ifndef T_SRV +#define T_SRV 33 +#endif /* T_SRV */ + +/* for old Unixes and friends ... */ +#ifndef MAXHOSTNAMELEN +#define MAXHOSTNAMELEN 64 +#endif + +#define MAX_DNS_NAMELEN (15*(MAXHOSTNAMELEN + 1)+1) + +/* + * Lookup a KDC via DNS SRV records + */ + +void krb5int_free_srv_dns_data (struct srv_dns_entry *p) +{ + struct srv_dns_entry *next; + while (p) { + next = p->next; + free(p->host); + free(p); + p = next; + } +} + +/* Do DNS SRV query, return results in *answers. + + Make best effort to return all the data we can. On memory or + decoding errors, just return what we've got. Always return 0, + currently. */ + +krb5_error_code +krb5int_make_srv_query_realm(const krb5_data *realm, + const char *service, + const char *protocol, + struct srv_dns_entry **answers) +{ + union { + unsigned char bytes[2048]; + HEADER hdr; + } answer; + unsigned char *p=NULL; + char host[MAX_DNS_NAMELEN], *h; + int type, rrclass; + int priority, weight, size, len, numanswers, numqueries, rdlen; + unsigned short port; + const int hdrsize = sizeof(HEADER); + + struct srv_dns_entry *head = NULL; + struct srv_dns_entry *srv = NULL, *entry = NULL; + + /* + * First off, build a query of the form: + * + * service.protocol.realm + * + * which will most likely be something like: + * + * _kerberos._udp.REALM + * + */ + + if (memchr(realm->data, 0, realm->length)) + return 0; + if ( strlen(service) + strlen(protocol) + realm->length + 6 + > MAX_DNS_NAMELEN ) + return 0; + sprintf(host, "%s.%s.%.*s", service, protocol, (int) realm->length, + realm->data); + + /* Realm names don't (normally) end with ".", but if the query + doesn't end with "." and doesn't get an answer as is, the + resolv code will try appending the local domain. Since the + realm names are absolutes, let's stop that. + + But only if a name has been specified. If we are performing + a search on the prefix alone then the intention is to allow + the local domain or domain search lists to be expanded. */ + + h = host + strlen (host); + if ((h[-1] != '.') && ((h - host + 1) < sizeof(host))) + strcpy (h, "."); + +#ifdef TEST + fprintf (stderr, "sending DNS SRV query for %s\n", host); +#endif + + size = res_search(host, C_IN, T_SRV, answer.bytes, sizeof(answer.bytes)); + + if ((size < hdrsize) || (size > sizeof(answer.bytes))) + goto out; + + /* + * We got an answer! First off, parse the header and figure out how + * many answers we got back. + */ + + p = answer.bytes; + + numqueries = ntohs(answer.hdr.qdcount); + numanswers = ntohs(answer.hdr.ancount); + + p += sizeof(HEADER); + + /* + * We need to skip over all of the questions, so we have to iterate + * over every query record. dn_expand() is able to tell us the size + * of compress DNS names, so we use it. + */ + +#define INCR_CHECK(x,y) x += y; if (x > size + answer.bytes) goto out +#define CHECK(x,y) if (x + y > size + answer.bytes) goto out +#define NTOHSP(x,y) x[0] << 8 | x[1]; x += y + + while (numqueries--) { + len = dn_expand(answer.bytes, answer.bytes + size, p, host, sizeof(host)); + if (len < 0) + goto out; + INCR_CHECK(p, len + 4); + } + + /* + * We're now pointing at the answer records. Only process them if + * they're actually T_SRV records (they might be CNAME records, + * for instance). + * + * But in a DNS reply, if you get a CNAME you always get the associated + * "real" RR for that CNAME. RFC 1034, 3.6.2: + * + * CNAME RRs cause special action in DNS software. When a name server + * fails to find a desired RR in the resource set associated with the + * domain name, it checks to see if the resource set consists of a CNAME + * record with a matching class. If so, the name server includes the CNAME + * record in the response and restarts the query at the domain name + * specified in the data field of the CNAME record. The one exception to + * this rule is that queries which match the CNAME type are not restarted. + * + * In other words, CNAMEs do not need to be expanded by the client. + */ + + while (numanswers--) { + + /* First is the name; use dn_expand to get the compressed size */ + len = dn_expand(answer.bytes, answer.bytes + size, p, host, sizeof(host)); + if (len < 0) + goto out; + INCR_CHECK(p, len); + + /* Next is the query type */ + CHECK(p, 2); + type = NTOHSP(p,2); + + /* Next is the query class; also skip over 4 byte TTL */ + CHECK(p, 6); + rrclass = NTOHSP(p,6); + + /* Record data length */ + + CHECK(p,2); + rdlen = NTOHSP(p,2); + + /* + * If this is an SRV record, process it. Record format is: + * + * Priority + * Weight + * Port + * Server name + */ + + if (rrclass == C_IN && type == T_SRV) { + CHECK(p,2); + priority = NTOHSP(p,2); + CHECK(p, 2); + weight = NTOHSP(p,2); + CHECK(p, 2); + port = NTOHSP(p,2); + len = dn_expand(answer.bytes, answer.bytes + size, p, host, sizeof(host)); + if (len < 0) + goto out; + INCR_CHECK(p, len); + + /* + * We got everything! Insert it into our list, but make sure + * it's in the right order. Right now we don't do anything + * with the weight field + */ + + srv = (struct srv_dns_entry *) malloc(sizeof(struct srv_dns_entry)); + if (srv == NULL) + goto out; + + srv->priority = priority; + srv->weight = weight; + srv->port = port; + srv->host = strdup(host); + if (srv->host == NULL) { + free(srv); + goto out; + } + + if (head == NULL || head->priority > srv->priority) { + srv->next = head; + head = srv; + } else + /* + * This is confusing. Only insert an entry into this + * spot if: + * The next person has a higher priority (lower priorities + * are preferred). + * Or + * There is no next entry (we're at the end) + */ + for (entry = head; entry != NULL; entry = entry->next) + if ((entry->next && + entry->next->priority > srv->priority) || + entry->next == NULL) { + srv->next = entry->next; + entry->next = srv; + break; + } + } else + INCR_CHECK(p, rdlen); + } + + out: + *answers = head; + return 0; +} +#endif
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