--- /dev/null
+/*
+ * 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 <unistd.h>
+#include <string.h>
+#include <signal.h>
+#include <arpa/inet.h>
+#include <ctype.h>
+#include "libbb.h"
+
+static char *fileconf = "/etc/dnsd.conf";
+#define LOCK_FILE "/var/run/dnsd.lock"
+#define LOG_FILE "/var/log/dnsd.log"
+
+#define MAX_HOST_LEN 16 // longest host name allowed is 15
+#define IP_STRING_LEN 18 // .xxx.xxx.xxx.xxx\0
+
+//must be strlen('.in-addr.arpa') larger than IP_STRING_LEN
+static const int 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
+*/
+static const int MAX_PACK_LEN = 512 + 1;
+
+#define DEFAULT_TTL 30; // increase this when not testing?
+
+static const int REQ_A = 1;
+static const int REQ_PTR = 12;
+
+struct dns_repl { // resource record, add 0 or 1 to accepted dns_msg in resp
+ uint16_t rlen;
+ uint8_t *r; // resource
+ uint16_t flags;
+};
+
+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 = NULL;
+static int daemonmode = 0;
+static uint32_t ttl = DEFAULT_TTL;
+
+/*
+ * 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 insetad 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++;
+ }
+}
+
+/*
+ * Append message to log file
+ */
+static void
+log_message(char *filename, char *message)
+{
+ FILE *logfile;
+ if (!daemonmode)
+ return;
+ logfile = fopen(filename, "a");
+ if (!logfile)
+ return;
+ fprintf(logfile, "%s\n", message);
+ fclose(logfile);
+}
+
+/*
+ * Read one line of hostname/IP from file
+ * Returns 0 for each valid entry read, -1 at EOF
+ * Assumes all host names are lower case only
+ * Hostnames with more than one label is not handled correctly.
+ * Presently the dot is copied into name without
+ * converting to a length/string substring for that label.
+ */
+
+static int
+getfileentry(FILE * fp, struct dns_entry *s, int verb)
+{
+ unsigned int a,b,c,d;
+ char *r, *name;
+
+restart:
+ if(!(r = bb_get_line_from_file(fp)))
+ return -1;
+ while(*r == ' ' || *r == '\t') {
+ r++;
+ if(!*r || *r == '#' || *r == '\n')
+ goto restart; /* skipping empty/blank and commented lines */
+ }
+ name = r;
+ while(*r != ' ' && *r != '\t')
+ r++;
+ *r++ = 0;
+ if(sscanf(r,"%u.%u.%u.%u",&a,&b,&c,&d) != 4)
+ goto restart; /* skipping wrong lines */
+
+ sprintf(s->ip,"%u.%u.%u.%u",a,b,c,d);
+ sprintf(s->rip,".%u.%u.%u.%u",d,c,b,a);
+ undot((uint8_t*)s->rip);
+ convname(s->name,(uint8_t*)name);
+
+ if(verb)
+ fprintf(stderr,"\tname:%s, ip:%s\n",&(s->name[1]),s->ip);
+
+ return 0; /* warningkiller */
+}
+
+/*
+ * Read hostname/IP records from file
+ */
+static void
+dnsentryinit(int verb)
+{
+ FILE *fp;
+ struct dns_entry *m, *prev;
+ prev = dnsentry = NULL;
+
+ if(!(fp = fopen(fileconf, "r")))
+ bb_perror_msg_and_die("open %s",fileconf);
+
+ while (1) {
+ if(!(m = (struct dns_entry *)malloc(sizeof(struct dns_entry))))
+ bb_perror_msg_and_die("malloc dns_entry");
+
+ m->next = NULL;
+ if (getfileentry(fp, m, verb))
+ break;
+
+ if (prev == NULL)
+ dnsentry = m;
+ else
+ prev->next = m;
+ prev = m;
+ }
+ fclose(fp);
+}
+
+
+/*
+ * Set up UDP socket
+ */
+static int
+listen_socket(char *iface_addr, int listen_port)
+{
+ struct sockaddr_in a;
+ char msg[100];
+ int s;
+ int yes = 1;
+ if ((s = socket(PF_INET, SOCK_DGRAM, 0)) < 0)
+ bb_perror_msg_and_die("socket() failed");
+#ifdef SO_REUSEADDR
+ if (setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&yes, sizeof(yes)) < 0)
+ bb_perror_msg_and_die("setsockopt() failed");
+#endif
+ memset(&a, 0, sizeof(a));
+ a.sin_port = htons(listen_port);
+ a.sin_family = AF_INET;
+ if (!inet_aton(iface_addr, &a.sin_addr))
+ bb_perror_msg_and_die("bad iface address");
+ if (bind(s, (struct sockaddr *)&a, sizeof(a)) < 0)
+ bb_perror_msg_and_die("bind() failed");
+ listen(s, 50);
+ sprintf(msg, "accepting UDP packets on addr:port %s:%d\n",
+ iface_addr, (int)listen_port);
+ log_message(LOG_FILE, msg);
+ return s;
+}
+
+/*
+ * 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 {
+#ifdef DEBUG
+ char *p,*q;
+ q = (char *)&(qs[1]);
+ p = &(d->name[1]);
+ fprintf(stderr, "\ntest: %d <%s> <%s> %d", strlen(p), p, q, 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])
+ continue;
+#ifdef DEBUG
+ fprintf(stderr, " OK");
+#endif
+ strcpy((char *)as, d->ip);
+#ifdef DEBUG
+ fprintf(stderr, " %s ", as);
+#endif
+ return 0;
+ }
+ else if (type == REQ_PTR) { /* search by IP-address */
+ if (!strncmp((char*)&d->rip[1], (char*)&qs[1], strlen(d->rip)-1)) {
+ strcpy((char *)as, d->name);
+ return 0;
+ }
+ }
+ } while ((d = d->next) != NULL);
+ return -1;
+}
+
+
+/*
+ * Decode message and generate answer
+ */
+#define eret(s) do { fprintf (stderr, "%s\n", s); return -1; } while (0)
+static int
+process_packet(uint8_t * buf)
+{
+ struct dns_head *head;
+ struct dns_prop *qprop;
+ struct dns_repl outr;
+ void *next, *from, *answb;
+
+ uint8_t answstr[MAX_NAME_LEN + 1];
+ int lookup_result, type, len, packet_len;
+ uint16_t flags;
+
+ answstr[0] = '\0';
+
+ head = (struct dns_head *)buf;
+ if (head->nquer == 0)
+ eret("no queries");
+
+ if ((head->flags & 0x8000))
+ eret("ignoring response packet");
+
+ from = (void *)&head[1]; // start of query string
+ next = answb = from + strlen((char *)&head[1]) + 1 + sizeof(struct dns_prop); // where to append answer block
+
+ outr.rlen = 0; // may change later
+ outr.r = NULL;
+ 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
+
+ log_message(LOG_FILE, (char *)head);
+ lookup_result = table_lookup(type, answstr, (uint8_t*)(&head[1]));
+ 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;
+ if (!inet_aton((char*)answstr, &a)) {//dotted dec to long conv
+ outr.flags = 1; /* Frmt err */
+ goto empty_packet;
+ }
+ memcpy(answstr, &a.s_addr, 4); // save before a disappears
+ outr.rlen = 4; // uint32_t IP
+ }
+ else
+ outr.rlen = strlen((char *)answstr) + 1; // a host name
+ outr.r = answstr; // 32 bit ip or a host name
+ outr.flags |= 0x0400; /* authority-bit */
+ // we have an answer
+ head->nansw = htons(1);
+
+ // copy query block to answer block
+ len = answb - from;
+ memcpy(answb, from, len);
+ next += len;
+
+ // and append answer rr
+ *(uint32_t *) next = htonl(ttl);
+ next += 4;
+ *(uint16_t *) next = htons(outr.rlen);
+ next += 2;
+ memcpy(next, (void *)answstr, outr.rlen);
+ next += 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 = htons(0);
+ head->nquer = htons(1);
+
+ packet_len = next - (void *)buf;
+ return packet_len;
+}
+
+/*
+ * Exit on signal
+ */
+static void
+interrupt(int x)
+{
+ unlink(LOCK_FILE);
+ write(2, "interrupt exiting\n", 18);
+ exit(2);
+}
+
+#define is_daemon() (flags&16)
+#define is_verbose() (flags&32)
+//#define DEBUG 1
+
+int dnsd_main(int argc, char **argv)
+{
+ int i, udps;
+ uint16_t port = 53;
+ uint8_t buf[MAX_PACK_LEN];
+ unsigned long flags = 0;
+ char *listen_interface = "0.0.0.0";
+ char *sttl=NULL, *sport=NULL;
+
+ if(argc > 1)
+ flags = bb_getopt_ulflags(argc, argv, "i:c:t:p:dv", &listen_interface, &fileconf, &sttl, &sport);
+ if(sttl)
+ if(!(ttl = atol(sttl)))
+ bb_show_usage();
+ if(sport)
+ if(!(port = atol(sport)))
+ bb_show_usage();
+
+ if(is_verbose()) {
+ fprintf(stderr,"listen_interface: %s\n", listen_interface);
+ fprintf(stderr,"ttl: %d, port: %d\n", ttl, port);
+ fprintf(stderr,"fileconf: %s\n", fileconf);
+ }
+
+ if(is_daemon())
+#if defined(__uClinux__)
+ /* reexec for vfork() do continue parent */
+ vfork_daemon_rexec(1, 0, argc, argv, "-d");
+#else /* uClinux */
+ if (daemon(1, 0) < 0) {
+ bb_perror_msg_and_die("daemon");
+ }
+#endif /* uClinuvx */
+
+ dnsentryinit(is_verbose());
+
+ signal(SIGINT, interrupt);
+ signal(SIGPIPE, SIG_IGN);
+ signal(SIGHUP, SIG_IGN);
+#ifdef SIGTSTP
+ signal(SIGTSTP, SIG_IGN);
+#endif
+#ifdef SIGURG
+ signal(SIGURG, SIG_IGN);
+#endif
+
+ udps = listen_socket(listen_interface, port);
+ if (udps < 0)
+ exit(1);
+
+ while (1) {
+ fd_set fdset;
+ int r;
+
+ FD_ZERO(&fdset);
+ FD_SET(udps, &fdset);
+ // Block until a message arrives
+ if((r = select(udps + 1, &fdset, NULL, NULL, NULL)) < 0)
+ bb_perror_msg_and_die("select error");
+ else
+ if(r == 0)
+ bb_perror_msg_and_die("select spurious return");
+
+ /* Can this test ever be false? */
+ if (FD_ISSET(udps, &fdset)) {
+ struct sockaddr_in from;
+ int fromlen = sizeof(from);
+ r = recvfrom(udps, buf, sizeof(buf), 0,
+ (struct sockaddr *)&from,
+ (void *)&fromlen);
+ if(is_verbose())
+ fprintf(stderr, "\n--- Got UDP ");
+ log_message(LOG_FILE, "\n--- Got UDP ");
+
+ if (r < 12 || r > 512) {
+ bb_error_msg("invalid packet size");
+ continue;
+ }
+ if (r > 0) {
+ r = process_packet(buf);
+ if (r > 0)
+ sendto(udps, buf,
+ r, 0, (struct sockaddr *)&from,
+ fromlen);
+ }
+ } // end if
+ } // end while
+ return 0;
+}
+
+
projects / oweals / busybox.git / commitdiff