[icmp-dn.git] / 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>

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