diff options
Diffstat (limited to 'networking')
| -rw-r--r-- | networking/Config.in | 6 | ||||
| -rw-r--r-- | networking/Makefile.in | 1 | ||||
| -rw-r--r-- | networking/dnsd.c | 469 |
3 files changed, 476 insertions, 0 deletions
diff --git a/networking/Config.in b/networking/Config.in index 7a29e0e..0f4381b 100644 --- a/networking/Config.in +++ b/networking/Config.in @@ -18,6 +18,12 @@ config CONFIG_ARPING help Ping hosts by ARP packets +config CONFIG_DNSD + bool "dnsd" + default n + help + Small and static DNS server deamon. + config CONFIG_ETHER_WAKE bool "ether-wake" default n diff --git a/networking/Makefile.in b/networking/Makefile.in index 2263acc..50eb450 100644 --- a/networking/Makefile.in +++ b/networking/Makefile.in @@ -12,6 +12,7 @@ srcdir=$(top_srcdir)/networking NETWORKING-y:= NETWORKING-$(CONFIG_ARPING) += arping.o +NETWORKING-$(CONFIG_DNSD) += dnsd.o NETWORKING-$(CONFIG_ETHER_WAKE) += ether-wake.o NETWORKING-$(CONFIG_FAKEIDENTD) += fakeidentd.o NETWORKING-$(CONFIG_FTPGET) += ftpgetput.o diff --git a/networking/dnsd.c b/networking/dnsd.c new file mode 100644 index 0000000..77d37d9 --- /dev/null +++ b/networking/dnsd.c @@ -0,0 +1,469 @@ +/* + * 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; +} + + |