slirp: resolve .local suffix DNS requests using the host's name resolution
(cherry picked from commit e2a6a4c1177e252bc38221c87bb99a599e8761a1)
This commit is contained in:
rakslice
parent
d547db0648
commit
a453ae105a
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@ -14,6 +14,26 @@
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#include <sys/filio.h>
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#endif
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#define DEBUG_HOST_RESOLVED_DNS 0
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/**
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* DNS requests for these domain suffixes will be
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* looked up on the host to allow for host-supported DNS alternatives
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* (e.g. MDNS, hosts file, etc.)
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**/
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static const char * host_resolved_domain_suffixes[] = {
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".local.",
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NULL // list ending
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};
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#define DOT_LOCAL_TTL 60 // In seconds. Keep this short as data is very dynamic and requerying is cheap
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#if DEBUG_HOST_RESOLVED_DNS
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#define D(...) printf(__VA_ARGS__); fflush(stdout);
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#else
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#define D(...)
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#endif
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void
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so_init()
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{
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@ -482,6 +502,270 @@ sorecvfrom(so)
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} /* if ping packet */
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}
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struct DNS_HEADER
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{
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unsigned short id; // identification number
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unsigned char rd :1; // recursion desired
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unsigned char tc :1; // truncated message
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unsigned char aa :1; // authoritive answer
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unsigned char opcode :4; // purpose of message
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unsigned char qr :1; // query/response flag
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unsigned char rcode :4; // response code
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unsigned char cd :1; // checking disabled
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unsigned char ad :1; // authenticated data
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unsigned char z :1; // its z! reserved
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unsigned char ra :1; // recursion available
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unsigned short q_count; // number of question entries
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unsigned short ans_count; // number of answer entries
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unsigned short auth_count; // number of authority entries
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unsigned short add_count; // number of resource entries
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};
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struct QUESTION
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{
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unsigned short qtype;
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unsigned short qclass;
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};
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#pragma pack(push, 1)
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struct R_DATA
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{
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unsigned short type;
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unsigned short _class;
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unsigned int ttl;
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unsigned short data_len;
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};
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#pragma pack(pop)
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#define POP_STRUCT(vartype, varname, data, len) \
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assert(len >= sizeof(vartype)); \
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vartype varname; \
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memcpy(&varname, data, sizeof(vartype)); \
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data += sizeof(vartype); \
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len -= sizeof(vartype)
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static void inject_udp_packet_to_guest(struct socket * so, struct sockaddr_in addr, caddr_t packet_data, int packet_len) {
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struct mbuf *m;
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int len;
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if (!(m = m_get())) return;
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m->m_data += if_maxlinkhdr;
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len = M_FREEROOM(m);
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if (packet_len > len) {
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packet_len = (m->m_data - m->m_dat) + m->m_len + packet_len + 1;
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m_inc(m, packet_len);
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len = M_FREEROOM(m);
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}
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assert(len >= packet_len);
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m->m_len = packet_len;
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memcpy(m->m_data, packet_data, packet_len);
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udp_output(so, m, &addr);
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}
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/* Decode hostname from the format used in DNS
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e.g. "\009something\004else\003com" for "something.else.com." */
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static char * decode_dns_name(char * data) {
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int query_str_len = strlen(data);
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char * decoded_name_str = malloc(query_str_len + 1);
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if (decoded_name_str == NULL) {
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D("decode_dns_name(): out of memory\n");
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return NULL; // oom
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}
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char * decoded_name_str_pos = decoded_name_str;
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while (*data != '\0') {
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int part_len = *data++;
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query_str_len--;
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if (query_str_len < part_len) {
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D("decode_dns_name(): part went off the end of the string\n");
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free(decoded_name_str);
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return NULL;
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}
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memcpy(decoded_name_str_pos, data, part_len);
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decoded_name_str_pos[part_len] = '.';
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decoded_name_str_pos += part_len + 1;
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query_str_len -= part_len;
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data += part_len;
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}
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*decoded_name_str_pos = '\0';
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return decoded_name_str;
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}
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/** Take a look at a UDP DNS request the client has made and see if we want to resolve it internally.
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* Returns TRUE if the request has been internally and can be dropped,
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* FALSE otherwise
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**/
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static BOOL resolve_dns_request(struct socket * so, struct sockaddr_in addr, caddr_t data, int len) {
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BOOL drop_dns_request = FALSE;
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D("Checking outgoing DNS UDP packet\n");
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if (len < sizeof(struct DNS_HEADER)) {
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D("Packet too short for DNS header\n");
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return FALSE;
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}
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const caddr_t packet = data;
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const int packet_len = len;
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POP_STRUCT(struct DNS_HEADER, h, data, len);
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if (h.qr != 0) {
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D("DNS packet is not a request\n");
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return FALSE;
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}
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if (ntohs(h.q_count) == 0) {
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D("DNS request has no queries\n");
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return FALSE;
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}
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if (ntohs(h.q_count) > 1) {
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D("DNS request has multiple queries (not supported)\n");
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return FALSE;
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}
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if (ntohs(h.ans_count != 0) || ntohs(h.auth_count != 0) || ntohs(h.add_count != 0)) {
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D("DNS request has unsupported extra contents\n");
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return FALSE;
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}
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if (len == 0) {
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D("Packet too short for DNS query string\n");
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return FALSE;
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}
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char * original_query_str = data;
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int query_str_len = strnlen(data, len);
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if (query_str_len == len) { // went off end of packet
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D("Unterminated DNS query string\n");
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return FALSE;
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}
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char * decoded_name_str = decode_dns_name(original_query_str);
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if (decoded_name_str == NULL) {
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D("Error while decoding DNS query string");
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return FALSE;
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}
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D("DNS host query for %s\n", decoded_name_str);
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data += query_str_len + 1;
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len -= query_str_len + 1;
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POP_STRUCT(struct QUESTION, qinfo, data, len);
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if (ntohs(qinfo.qtype) != 1 || ntohs(qinfo.qclass) != 1) {
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D("DNS host query for %s: Request isn't the supported type (INET A query)\n", decoded_name_str);
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free(decoded_name_str);
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return FALSE;
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}
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D("DNS host query for %s: Request is eligible to check for host resolution suffix\n", decoded_name_str);
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const char * matched_suffix = NULL;
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for (const char ** suffix_ptr = host_resolved_domain_suffixes; *suffix_ptr != NULL; suffix_ptr++) {
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const char * suffix = *suffix_ptr;
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int suffix_pos = strlen(decoded_name_str) - strlen(suffix);
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if (suffix_pos > 0 && strcmp(decoded_name_str + suffix_pos, suffix) == 0) {
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matched_suffix = suffix;
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break;
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}
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}
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if (matched_suffix == NULL) {
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D("DNS host query for %s: No suffix matched\n", decoded_name_str);
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} else {
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D("DNS host query for %s: Suffix matched: %s\n", decoded_name_str, matched_suffix);
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// we are going to take this request and resolve it on the host
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drop_dns_request = TRUE;
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D("DNS host query for %s: Doing lookup on host\n", decoded_name_str);
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int results_count = 0;
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struct hostent * host_lookup_result = gethostbyname(decoded_name_str);
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if (host_lookup_result && host_lookup_result->h_addrtype == AF_INET) {
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D("DNS host query for %s: Host response has results for AF_INET\n", decoded_name_str);
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for (char ** addr_entry = host_lookup_result->h_addr_list; *addr_entry != NULL; addr_entry++) {
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++results_count;
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}
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}
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D("DNS host query for %s: result count %d\n", decoded_name_str, results_count);
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int original_query_str_size = strlen(original_query_str) + 1;
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int response_size = packet_len + results_count * (original_query_str_size + sizeof(struct R_DATA) + sizeof(struct in_addr));
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caddr_t response_packet = malloc(response_size);
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if (response_packet == NULL) {
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D("DNS host query for %s: Out of memory while allocating DNS response packet\n", decoded_name_str);
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} else {
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D("DNS host query for %s: Preparing DNS response\n", decoded_name_str);
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// use the request DNS header as our starting point for the response
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h.qr = 1;
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h.ans_count = htons(results_count);
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memcpy(response_packet, &h, sizeof(struct DNS_HEADER));
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// other sections verbatim out of the request
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memcpy(response_packet + sizeof(struct DNS_HEADER), packet + sizeof(struct DNS_HEADER), packet_len - sizeof(struct DNS_HEADER));
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int response_pos = packet_len;
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if (results_count > 0) {
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for (char ** addr_entry = host_lookup_result->h_addr_list; *addr_entry != NULL; addr_entry++) {
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// answer string is verbatim from question
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memcpy(response_packet + response_pos, original_query_str, original_query_str_size);
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response_pos += original_query_str_size;
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struct R_DATA resource;
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resource.type = htons(1);
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resource._class = htons(1);
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resource.ttl = htonl(DOT_LOCAL_TTL);
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resource.data_len = htons(sizeof(struct in_addr));
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memcpy(response_packet + response_pos, &resource, sizeof(struct R_DATA));
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response_pos += sizeof(struct R_DATA);
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struct in_addr * cur_addr = (struct in_addr *)*addr_entry;
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memcpy(response_packet + response_pos, cur_addr, sizeof(struct in_addr));
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response_pos += sizeof(struct in_addr);
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}
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assert(response_pos == response_size);
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}
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D("DNS host query for %s: Injecting DNS response directly to guest\n", decoded_name_str);
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inject_udp_packet_to_guest(so, addr, response_packet, response_size);
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free(response_packet);
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}
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}
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free(decoded_name_str);
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D("DNS host request drop: %s\n", drop_dns_request? "yes" : "no");
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return drop_dns_request;
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}
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/*
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* sendto() a socket
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*/
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@ -503,6 +787,8 @@ sosendto(so, m)
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switch(ntohl(so->so_faddr.s_addr) & 0xff) {
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case CTL_DNS:
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addr.sin_addr = dns_addr;
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if (resolve_dns_request(so, addr, m->m_data, m->m_len))
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return 0;
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break;
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case CTL_ALIAS:
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default:
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