[icmp-dn.git] / src / icmpdnd.c

/*
 *  icmpdnd - ICMP Domain Name responder daemon for Linux
 *  Copyright (C) 2005 Fredrik Tolf <fredrik@dolda2000.com>
 *  
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *  
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *  
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
*/
#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <syslog.h>
#include <time.h>
#include <sys/socket.h>
#include <sys/poll.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netinet/ip.h>
#include <sys/types.h>
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

struct icmphdr {
    u_int8_t type;
    u_int8_t code;
    u_int16_t checksum;
};

struct reqhdr {
    u_int8_t type;
    u_int8_t code;
    u_int16_t checksum;
    u_int16_t id;
    u_int16_t seq;
};

struct rephdr {
    u_int8_t type;
    u_int8_t code;
    u_int16_t checksum;
    u_int16_t id;
    u_int16_t seq;
    int32_t ttl;
};

#define ICMP_NAMEREQ 37
#define ICMP_NAMEREP 38

volatile int alive;

size_t filldn(char *dst)
{
    char *p, *p2, *dp;
    char namebuf[1024];
    int hl;
    
    if(gethostname(namebuf, sizeof(namebuf)) < 0) {
	perror("gethostname");
	exit(1);
    }
    hl = strlen(namebuf);
    namebuf[hl++] = '.';
    if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) {
	perror("getdomainname");
	exit(1);
    }
    if(strlen(namebuf + hl) != 0) {
	hl = strlen(namebuf);
	namebuf[hl++] = '.';
    }
    namebuf[hl] = 0;
    
    p = namebuf;
    dp = dst;
    while((p2 = strchr(p, '.')) != NULL) {
	*p2 = 0;
	*(dp++) = p2 - p;
	memcpy(dp, p, p2 - p);
	dp += p2 - p;
	p = p2 + 1;
    }
    *(dp++) = 0;
    
    return(dp - dst);
}

void cksum(void *hdr, size_t len)
{
    struct icmphdr *ih;
    u_int8_t *cb;
    int i;
    int b1, b2;
    
    ih = (struct icmphdr *)hdr;
    cb = (u_int8_t *)hdr;
    ih->checksum = 0;
    b1 = b2 = 0;
    for(i = 0; i < (len & ~1); i += 2) {
	b1 += cb[i];
	b2 += cb[i + 1];
    }
    if(i & 1)
	b1 += cb[len - 1];
    while(1) {
	if(b1 >= 256) {
	    b2 += b1 >> 8;
	    b1 &= 0xff;
	    continue;
	}
	if(b2 >= 256) {
	    b1 += b2 >> 8;
	    b2 &= 0xff;
	    continue;
	}
	break;
    }
    cb = (u_int8_t *)&ih->checksum;
    cb[0] = ~(u_int8_t)b1;
    cb[1] = ~(u_int8_t)b2;
}

int main(int argc, char **argv)
{
    int i, n, ret;
    int c, cs, s4, s6, datalen;
    int daemonize, ttl;
    unsigned char buf[65536];
    struct sockaddr_storage name;
    struct reqhdr req;
    struct rephdr rep;
    struct iphdr iphdr;
    struct msghdr mhdr;
    struct iovec iov;
    char cmsgbuf[CMSG_SPACE(sizeof(struct in6_pktinfo))];
    size_t hdrlen;
    struct pollfd pfd[2];
    time_t curtime, lasterr;
    
    daemonize = 1;
    ttl = 3600;
    while((c = getopt(argc, argv, "nht:")) != -1) {
	switch(c) {
	case 't':
	    ttl = atoi(optarg);
	    break;
	case 'n':
	    daemonize = 0;
	    break;
	case 'h':
	case '?':
	case ':':
	default:
	    fprintf(stderr, "usage: icmpdnd [-n]");
	    exit((c == 'h')?0:1);
	}
    }
    
    s4 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
    s6 = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMP);
    if((s4 < 0) && (s6 < 0)) {
	perror("could not open raw socket");
	exit(1);
    }
    if(s6 >= 0) {
	i = 1;
	if(setsockopt(s6, IPPROTO_IPV6, IPV6_PKTINFO, &i, sizeof(i))) {
	    perror("could not set IPV6_PKTINFO sockopt");
	    exit(1);
	}
    }
    
    if(daemonize)
	daemon(0, 0);
    
    openlog("icmpdnd", LOG_PID | LOG_NDELAY, LOG_DAEMON);
    
    alive = 1;
    lasterr = 0;
    while(alive) {
	n = 0;
	if(s4 >= 0) {
	    pfd[n].fd = s4;
	    pfd[n].events = POLLIN;
	    n++;
	}
	if(s6 >= 0) {
	    pfd[n].fd = s6;
	    pfd[n].events = POLLIN;
	    n++;
	}
	ret = poll(pfd, n, -1);

	curtime = time(NULL);
	if(ret < 0) {
	    if(errno == EINTR)
		continue;
	    syslog(LOG_ERR, "error while polling sockets: %m");
	    if(lasterr == curtime) {
		syslog(LOG_CRIT, "exiting due to repeated errors");
		exit(1);
	    }
	    lasterr = curtime;
	}
	
	for(i = 0; i < n; i++) {
	    if((pfd[i].revents & POLLIN) == 0)
		continue;
	    cs = pfd[i].fd;
	    memset(&name, 0, sizeof(name));
	    
	    iov.iov_len = sizeof(buf);
	    iov.iov_base = buf;
	    mhdr.msg_name = &name;
	    mhdr.msg_namelen = sizeof(name);
	    mhdr.msg_iov = &iov;
	    mhdr.msg_iovlen = 1;
	    mhdr.msg_control = cmsgbuf;
	    mhdr.msg_controllen = sizeof(cmsgbuf);
	    
	    ret = recvmsg(cs, &mhdr, 0);
	    if(ret < 0) {
		syslog(LOG_WARNING, "error while receiving datagram: %m");
		continue;
	    }
	    
	    if(cs == s4) {
		if(ret < sizeof(iphdr) + sizeof(req))
		    continue;
		hdrlen = sizeof(iphdr);
		memcpy(&iphdr, buf, sizeof(iphdr));
		if(iphdr.protocol != IPPROTO_ICMP)
		    continue;
		mhdr.msg_control = NULL;
		mhdr.msg_controllen = 0;
	    } else if(cs == s6) {
		if(ret < sizeof(req))
		    continue;
		((struct sockaddr_in6 *)&name)->sin6_port = 0;
		hdrlen = 0;
		/* Just keep mhdr.msg_control. */
	    } else {
		syslog(LOG_CRIT, "strangeness!");
		abort();
	    }
	    memcpy(&req, buf + hdrlen, sizeof(req));
	    if(req.type != ICMP_NAMEREQ)
		continue;
	    rep.type = ICMP_NAMEREP;
	    rep.code = 0;
	    rep.id = req.id;
	    rep.seq = req.seq;
	    rep.ttl = htonl(ttl);
	    memcpy(buf, &rep, sizeof(rep));
	    datalen = filldn(buf + sizeof(rep));
	
	    cksum(buf, datalen + sizeof(rep));
	    
	    iov.iov_len = sizeof(rep) + datalen;
	    iov.iov_base = buf;
	    mhdr.msg_iov = &iov;
	    mhdr.msg_iovlen = 1;
	    ret = sendmsg(cs, &mhdr, 0);
	    if(ret < 0)
		syslog(LOG_WARNING, "error in sending reply: %m");
	}
    }
    
    close(s4);
    close(s6);
    return(0);
}

/*
 * Local Variables:
 * compile-command: "gcc -Wall -g -o icmpdnd icmpdnd.c"
 * End:
 */
Commit	Line	Data
fa6ac2fc DC	1	/*
fa6ac2fc DC	2	* icmpdnd - ICMP Domain Name responder daemon for Linux
b39da562	3	* Copyright (C) 2005 Fredrik Tolf <fredrik@dolda2000.com>
fa6ac2fc DC	4	*
	5	* This program is free software; you can redistribute it and/or modify
	6	* it under the terms of the GNU General Public License as published by
	7	* the Free Software Foundation; either version 2 of the License, or
	8	* (at your option) any later version.
	9	*
	10	* This program is distributed in the hope that it will be useful,
	11	* but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
	13	* GNU General Public License for more details.
	14	*
	15	* You should have received a copy of the GNU General Public License
	16	* along with this program; if not, write to the Free Software
	17	* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
	18	*/
	19	#include <stdlib.h>
	20	#include <unistd.h>
	21	#include <stdio.h>
	22	#include <string.h>
	23	#include <errno.h>
b39da562	24	#include <syslog.h>
dcb0aee6	25	#include <time.h>
fa6ac2fc	26	#include <sys/socket.h>
6796167f	27	#include <sys/poll.h>
fa6ac2fc DC	28	#include <netinet/in.h>
	29	#include <arpa/inet.h>
	30	#include <netinet/ip.h>
	31	#include <sys/types.h>
606a39c9	32	#ifdef HAVE_CONFIG_H
2269406c	33	#include "config.h"
606a39c9	34	#endif
fa6ac2fc DC	35
	36	struct icmphdr {
	37	u_int8_t type;
	38	u_int8_t code;
	39	u_int16_t checksum;
	40	};
	41
	42	struct reqhdr {
	43	u_int8_t type;
	44	u_int8_t code;
	45	u_int16_t checksum;
	46	u_int16_t id;
	47	u_int16_t seq;
	48	};
	49
	50	struct rephdr {
	51	u_int8_t type;
	52	u_int8_t code;
	53	u_int16_t checksum;
	54	u_int16_t id;
	55	u_int16_t seq;
	56	int32_t ttl;
	57	};
	58
	59	#define ICMP_NAMEREQ 37
	60	#define ICMP_NAMEREP 38
	61
fa6ac2fc DC	62	volatile int alive;
	63
	64	size_t filldn(char *dst)
	65	{
	66	char p, p2, *dp;
	67	char namebuf[1024];
	68	int hl;
	69
	70	if(gethostname(namebuf, sizeof(namebuf)) < 0) {
	71	perror("gethostname");
	72	exit(1);
	73	}
	74	hl = strlen(namebuf);
	75	namebuf[hl++] = '.';
	76	if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) {
	77	perror("getdomainname");
	78	exit(1);
	79	}
	80	if(strlen(namebuf + hl) != 0) {
	81	hl = strlen(namebuf);
	82	namebuf[hl++] = '.';
	83	}
	84	namebuf[hl] = 0;
	85
	86	p = namebuf;
	87	dp = dst;
	88	while((p2 = strchr(p, '.')) != NULL) {
	89	*p2 = 0;
	90	*(dp++) = p2 - p;
	91	memcpy(dp, p, p2 - p);
	92	dp += p2 - p;
	93	p = p2 + 1;
	94	}
	95	*(dp++) = 0;
	96
	97	return(dp - dst);
	98	}
	99
	100	void cksum(void *hdr, size_t len)
	101	{
	102	struct icmphdr *ih;
	103	u_int8_t *cb;
	104	int i;
	105	int b1, b2;
	106
	107	ih = (struct icmphdr *)hdr;
	108	cb = (u_int8_t *)hdr;
	109	ih->checksum = 0;
	110	b1 = b2 = 0;
	111	for(i = 0; i < (len & ~1); i += 2) {
	112	b1 += cb[i];
	113	b2 += cb[i + 1];
	114	}
	115	if(i & 1)
	116	b1 += cb[len - 1];
	117	while(1) {
	118	if(b1 >= 256) {
	119	b2 += b1 >> 8;
	120	b1 &= 0xff;
	121	continue;
	122	}
	123	if(b2 >= 256) {
	124	b1 += b2 >> 8;
	125	b2 &= 0xff;
126	continue;
127	}
128	break;
129	}
130	cb = (u_int8_t *)&ih->checksum;
131	cb[0] = ~(u_int8_t)b1;
132	cb[1] = ~(u_int8_t)b2;
133	}
134
135	int main(int argc, char **argv)
136	{
6796167f	137	int i, n, ret;
df4e01a5	138	int c, cs, s4, s6, datalen;
b39da562	139	int daemonize, ttl;
fa6ac2fc	140	unsigned char buf[65536];
6796167f	141	struct sockaddr_storage name;
fa6ac2fc DC	142	struct reqhdr req;
	143	struct rephdr rep;
	144	struct iphdr iphdr;
df4e01a5 DC	145	struct msghdr mhdr;
	146	struct iovec iov;
	147	char cmsgbuf[CMSG_SPACE(sizeof(struct in6_pktinfo))];
6796167f DC	148	size_t hdrlen;
6796167f DC	149	struct pollfd pfd[2];
dcb0aee6	150	time_t curtime, lasterr;
b39da562 DC	151
	152	daemonize = 1;
	153	ttl = 3600;
	154	while((c = getopt(argc, argv, "nht:")) != -1) {
	155	switch(c) {
	156	case 't':
	157	ttl = atoi(optarg);
	158	break;
	159	case 'n':
	160	daemonize = 0;
	161	break;
	162	case 'h':
	163	case '?':
	164	case ':':
	165	default:
	166	fprintf(stderr, "usage: icmpdnd [-n]");
	167	exit((c == 'h')?0:1);
	168	}
	169	}
	170
6796167f DC	171	s4 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
	172	s6 = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMP);
	173	if((s4 < 0) && (s6 < 0)) {
	174	perror("could not open raw socket");
fa6ac2fc DC	175	exit(1);
fa6ac2fc DC	176	}
df4e01a5 DC	177	if(s6 >= 0) {
	178	i = 1;
	179	if(setsockopt(s6, IPPROTO_IPV6, IPV6_PKTINFO, &i, sizeof(i))) {
	180	perror("could not set IPV6_PKTINFO sockopt");
	181	exit(1);
	182	}
	183	}
fa6ac2fc	184
b39da562 DC	185	if(daemonize)
	186	daemon(0, 0);
	187
6796167f	188	openlog("icmpdnd", LOG_PID \| LOG_NDELAY, LOG_DAEMON);
b39da562	189
fa6ac2fc	190	alive = 1;
dcb0aee6	191	lasterr = 0;
fa6ac2fc	192	while(alive) {
6796167f DC	193	n = 0;
	194	if(s4 >= 0) {
	195	pfd[n].fd = s4;
	196	pfd[n].events = POLLIN;
	197	n++;
	198	}
	199	if(s6 >= 0) {
	200	pfd[n].fd = s6;
	201	pfd[n].events = POLLIN;
	202	n++;
	203	}
	204	ret = poll(pfd, n, -1);
	205
dcb0aee6	206	curtime = time(NULL);
fa6ac2fc DC	207	if(ret < 0) {
	208	if(errno == EINTR)
	209	continue;
6796167f	210	syslog(LOG_ERR, "error while polling sockets: %m");
dcb0aee6 DC	211	if(lasterr == curtime) {
	212	syslog(LOG_CRIT, "exiting due to repeated errors");
	213	exit(1);
	214	}
	215	lasterr = curtime;
fa6ac2fc	216	}
dcb0aee6	217
6796167f DC	218	for(i = 0; i < n; i++) {
	219	if((pfd[i].revents & POLLIN) == 0)
	220	continue;
	221	cs = pfd[i].fd;
6796167f	222	memset(&name, 0, sizeof(name));
df4e01a5 DC	223
	224	iov.iov_len = sizeof(buf);
	225	iov.iov_base = buf;
	226	mhdr.msg_name = &name;
	227	mhdr.msg_namelen = sizeof(name);
	228	mhdr.msg_iov = &iov;
	229	mhdr.msg_iovlen = 1;
	230	mhdr.msg_control = cmsgbuf;
	231	mhdr.msg_controllen = sizeof(cmsgbuf);
	232
	233	ret = recvmsg(cs, &mhdr, 0);
6796167f DC	234	if(ret < 0) {
	235	syslog(LOG_WARNING, "error while receiving datagram: %m");
	236	continue;
	237	}
	238
	239	if(cs == s4) {
	240	if(ret < sizeof(iphdr) + sizeof(req))
	241	continue;
	242	hdrlen = sizeof(iphdr);
	243	memcpy(&iphdr, buf, sizeof(iphdr));
	244	if(iphdr.protocol != IPPROTO_ICMP)
	245	continue;
df4e01a5 DC	246	mhdr.msg_control = NULL;
df4e01a5 DC	247	mhdr.msg_controllen = 0;
6796167f DC	248	} else if(cs == s6) {
	249	if(ret < sizeof(req))
	250	continue;
	251	((struct sockaddr_in6 *)&name)->sin6_port = 0;
	252	hdrlen = 0;
df4e01a5	253	/* Just keep mhdr.msg_control. */
6796167f DC	254	} else {
	255	syslog(LOG_CRIT, "strangeness!");
	256	abort();
	257	}
	258	memcpy(&req, buf + hdrlen, sizeof(req));
	259	if(req.type != ICMP_NAMEREQ)
	260	continue;
	261	rep.type = ICMP_NAMEREP;
	262	rep.code = 0;
	263	rep.id = req.id;
	264	rep.seq = req.seq;
	265	rep.ttl = htonl(ttl);
	266	memcpy(buf, &rep, sizeof(rep));
	267	datalen = filldn(buf + sizeof(rep));
b39da562	268
6796167f	269	cksum(buf, datalen + sizeof(rep));
df4e01a5 DC	270
	271	iov.iov_len = sizeof(rep) + datalen;
	272	iov.iov_base = buf;
	273	mhdr.msg_iov = &iov;
	274	mhdr.msg_iovlen = 1;
	275	ret = sendmsg(cs, &mhdr, 0);
6796167f DC	276	if(ret < 0)
	277	syslog(LOG_WARNING, "error in sending reply: %m");
	278	}
fa6ac2fc DC	279	}
fa6ac2fc DC	280
6796167f DC	281	close(s4);
6796167f DC	282	close(s6);
fa6ac2fc DC	283	return(0);
fa6ac2fc DC	284	}
f82409dd DC	285
	286	/*
	287	* Local Variables:
	288	* compile-command: "gcc -Wall -g -o icmpdnd icmpdnd.c"
	289	* End:
	290	*/