[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>
#include "config.h"

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>
2269406c	32	#include "config.h"
fa6ac2fc DC	33
	34	struct icmphdr {
	35	u_int8_t type;
	36	u_int8_t code;
	37	u_int16_t checksum;
	38	};
	39
	40	struct reqhdr {
	41	u_int8_t type;
	42	u_int8_t code;
	43	u_int16_t checksum;
	44	u_int16_t id;
	45	u_int16_t seq;
	46	};
	47
	48	struct rephdr {
	49	u_int8_t type;
	50	u_int8_t code;
	51	u_int16_t checksum;
	52	u_int16_t id;
	53	u_int16_t seq;
	54	int32_t ttl;
	55	};
	56
	57	#define ICMP_NAMEREQ 37
	58	#define ICMP_NAMEREP 38
	59
fa6ac2fc DC	60	volatile int alive;
	61
	62	size_t filldn(char *dst)
	63	{
	64	char p, p2, *dp;
	65	char namebuf[1024];
	66	int hl;
	67
	68	if(gethostname(namebuf, sizeof(namebuf)) < 0) {
	69	perror("gethostname");
	70	exit(1);
	71	}
	72	hl = strlen(namebuf);
	73	namebuf[hl++] = '.';
	74	if(getdomainname(namebuf + hl, sizeof(namebuf) - hl) < 0) {
	75	perror("getdomainname");
	76	exit(1);
	77	}
	78	if(strlen(namebuf + hl) != 0) {
	79	hl = strlen(namebuf);
	80	namebuf[hl++] = '.';
	81	}
	82	namebuf[hl] = 0;
	83
	84	p = namebuf;
	85	dp = dst;
	86	while((p2 = strchr(p, '.')) != NULL) {
	87	*p2 = 0;
	88	*(dp++) = p2 - p;
	89	memcpy(dp, p, p2 - p);
	90	dp += p2 - p;
	91	p = p2 + 1;
	92	}
	93	*(dp++) = 0;
	94
	95	return(dp - dst);
	96	}
	97
	98	void cksum(void *hdr, size_t len)
	99	{
	100	struct icmphdr *ih;
	101	u_int8_t *cb;
	102	int i;
	103	int b1, b2;
	104
	105	ih = (struct icmphdr *)hdr;
	106	cb = (u_int8_t *)hdr;
	107	ih->checksum = 0;
	108	b1 = b2 = 0;
	109	for(i = 0; i < (len & ~1); i += 2) {
	110	b1 += cb[i];
	111	b2 += cb[i + 1];
	112	}
	113	if(i & 1)
	114	b1 += cb[len - 1];
	115	while(1) {
	116	if(b1 >= 256) {
	117	b2 += b1 >> 8;
	118	b1 &= 0xff;
	119	continue;
	120	}
	121	if(b2 >= 256) {
	122	b1 += b2 >> 8;
	123	b2 &= 0xff;
124	continue;
125	}
126	break;
127	}
128	cb = (u_int8_t *)&ih->checksum;
129	cb[0] = ~(u_int8_t)b1;
130	cb[1] = ~(u_int8_t)b2;
131	}
132
133	int main(int argc, char **argv)
134	{
6796167f	135	int i, n, ret;
df4e01a5	136	int c, cs, s4, s6, datalen;
b39da562	137	int daemonize, ttl;
fa6ac2fc	138	unsigned char buf[65536];
6796167f	139	struct sockaddr_storage name;
fa6ac2fc DC	140	struct reqhdr req;
	141	struct rephdr rep;
	142	struct iphdr iphdr;
df4e01a5 DC	143	struct msghdr mhdr;
	144	struct iovec iov;
	145	char cmsgbuf[CMSG_SPACE(sizeof(struct in6_pktinfo))];
6796167f DC	146	size_t hdrlen;
6796167f DC	147	struct pollfd pfd[2];
dcb0aee6	148	time_t curtime, lasterr;
b39da562 DC	149
	150	daemonize = 1;
	151	ttl = 3600;
	152	while((c = getopt(argc, argv, "nht:")) != -1) {
	153	switch(c) {
	154	case 't':
	155	ttl = atoi(optarg);
	156	break;
	157	case 'n':
	158	daemonize = 0;
	159	break;
	160	case 'h':
	161	case '?':
	162	case ':':
	163	default:
	164	fprintf(stderr, "usage: icmpdnd [-n]");
	165	exit((c == 'h')?0:1);
	166	}
	167	}
	168
6796167f DC	169	s4 = socket(PF_INET, SOCK_RAW, IPPROTO_ICMP);
	170	s6 = socket(PF_INET6, SOCK_RAW, IPPROTO_ICMP);
	171	if((s4 < 0) && (s6 < 0)) {
	172	perror("could not open raw socket");
fa6ac2fc DC	173	exit(1);
fa6ac2fc DC	174	}
df4e01a5 DC	175	if(s6 >= 0) {
	176	i = 1;
	177	if(setsockopt(s6, IPPROTO_IPV6, IPV6_PKTINFO, &i, sizeof(i))) {
	178	perror("could not set IPV6_PKTINFO sockopt");
	179	exit(1);
	180	}
	181	}
fa6ac2fc	182
b39da562 DC	183	if(daemonize)
	184	daemon(0, 0);
	185
6796167f	186	openlog("icmpdnd", LOG_PID \| LOG_NDELAY, LOG_DAEMON);
b39da562	187
fa6ac2fc	188	alive = 1;
dcb0aee6	189	lasterr = 0;
fa6ac2fc	190	while(alive) {
6796167f DC	191	n = 0;
	192	if(s4 >= 0) {
	193	pfd[n].fd = s4;
	194	pfd[n].events = POLLIN;
	195	n++;
	196	}
	197	if(s6 >= 0) {
	198	pfd[n].fd = s6;
	199	pfd[n].events = POLLIN;
	200	n++;
	201	}
	202	ret = poll(pfd, n, -1);
	203
dcb0aee6	204	curtime = time(NULL);
fa6ac2fc DC	205	if(ret < 0) {
	206	if(errno == EINTR)
	207	continue;
6796167f	208	syslog(LOG_ERR, "error while polling sockets: %m");
dcb0aee6 DC	209	if(lasterr == curtime) {
	210	syslog(LOG_CRIT, "exiting due to repeated errors");
	211	exit(1);
	212	}
	213	lasterr = curtime;
fa6ac2fc	214	}
dcb0aee6	215
6796167f DC	216	for(i = 0; i < n; i++) {
	217	if((pfd[i].revents & POLLIN) == 0)
	218	continue;
	219	cs = pfd[i].fd;
6796167f	220	memset(&name, 0, sizeof(name));
df4e01a5 DC	221
	222	iov.iov_len = sizeof(buf);
	223	iov.iov_base = buf;
	224	mhdr.msg_name = &name;
	225	mhdr.msg_namelen = sizeof(name);
	226	mhdr.msg_iov = &iov;
	227	mhdr.msg_iovlen = 1;
	228	mhdr.msg_control = cmsgbuf;
	229	mhdr.msg_controllen = sizeof(cmsgbuf);
	230
	231	ret = recvmsg(cs, &mhdr, 0);
6796167f DC	232	if(ret < 0) {
	233	syslog(LOG_WARNING, "error while receiving datagram: %m");
	234	continue;
	235	}
	236
	237	if(cs == s4) {
	238	if(ret < sizeof(iphdr) + sizeof(req))
	239	continue;
	240	hdrlen = sizeof(iphdr);
	241	memcpy(&iphdr, buf, sizeof(iphdr));
	242	if(iphdr.protocol != IPPROTO_ICMP)
	243	continue;
df4e01a5 DC	244	mhdr.msg_control = NULL;
df4e01a5 DC	245	mhdr.msg_controllen = 0;
6796167f DC	246	} else if(cs == s6) {
	247	if(ret < sizeof(req))
	248	continue;
	249	((struct sockaddr_in6 *)&name)->sin6_port = 0;
	250	hdrlen = 0;
df4e01a5	251	/* Just keep mhdr.msg_control. */
6796167f DC	252	} else {
	253	syslog(LOG_CRIT, "strangeness!");
	254	abort();
	255	}
	256	memcpy(&req, buf + hdrlen, sizeof(req));
	257	if(req.type != ICMP_NAMEREQ)
	258	continue;
	259	rep.type = ICMP_NAMEREP;
	260	rep.code = 0;
	261	rep.id = req.id;
	262	rep.seq = req.seq;
	263	rep.ttl = htonl(ttl);
	264	memcpy(buf, &rep, sizeof(rep));
	265	datalen = filldn(buf + sizeof(rep));
b39da562	266
6796167f	267	cksum(buf, datalen + sizeof(rep));
df4e01a5 DC	268
	269	iov.iov_len = sizeof(rep) + datalen;
	270	iov.iov_base = buf;
	271	mhdr.msg_iov = &iov;
	272	mhdr.msg_iovlen = 1;
	273	ret = sendmsg(cs, &mhdr, 0);
6796167f DC	274	if(ret < 0)
	275	syslog(LOG_WARNING, "error in sending reply: %m");
	276	}
fa6ac2fc DC	277	}
fa6ac2fc DC	278
6796167f DC	279	close(s4);
6796167f DC	280	close(s6);
fa6ac2fc DC	281	return(0);
fa6ac2fc DC	282	}
f82409dd DC	283
	284	/*
	285	* Local Variables:
	286	* compile-command: "gcc -Wall -g -o icmpdnd icmpdnd.c"
	287	* End:
	288	*/