new applet. Thanks Roberto A. Foglietta

AUTHORS

@@ -159,3 +159,6 @@ Tito Ragusa <farmatito@tiscali.it>
 
 Paul Fox <pgf@foxharp.boston.ma.us>
     vi editing mode for ash, various other patches/fixes
+
+Roberto A. Foglietta <me@roberto.foglietta.name>
+    port: dnsd

examples/dnsd.conf

@@ -0,0 +1 @@
+thebox 192.168.1.5

include/applets.h

@@ -164,6 +164,9 @@
 #ifdef CONFIG_DMESG
 	APPLET(dmesg, dmesg_main, _BB_DIR_BIN, _BB_SUID_NEVER)
 #endif
+#ifdef CONFIG_DNSD
+	APPLET(dnsd, dnsd_main, _BB_DIR_USR_SBIN, _BB_SUID_ALWAYS)
+#endif
 #ifdef CONFIG_DOS2UNIX
 	APPLET(dos2unix, dos2unix_main, _BB_DIR_USR_BIN, _BB_SUID_NEVER)
 #endif

include/usage.h

@@ -469,6 +469,17 @@
 	"\t-n LEVEL\tSets console logging level\n" \
 	"\t-s SIZE\t\tUse a buffer of size SIZE"
 
+#define dnsd_trivial_usage \
+        "[-c config] [-t seconds] [-p port] [-i iface-ip] [-d]"
+#define dnsd_full_usage \
+        "Small and static DNS server daemon\n\n" \
+	"Options:\n" \
+	"\t-c\t\tconfig filename\n" \
+	"\t-t\t\tTTL in seconds\n" \
+	"\t-p\t\tlistening port\n" \
+	"\t-i\t\tlistening iface ip (default all)\n" \
+	"\t-d\t\tdaemonize"
+
 #define dos2unix_trivial_usage \
 	"[option] [FILE]"
 #define dos2unix_full_usage \

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

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

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;
+}
+
+