/* Copyright (c) 2006 Simon Kelley
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; version 2 dated June, 1991.
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.
*/
/* dhcp_release <interface> <address> <MAC address> <client_id>
MUST be run as root - will fail otherwise. */
/* Send a DHCPRELEASE message via the specified interface
to tell the local DHCP server to delete a particular lease.
The interface argument is the interface in which a DHCP
request _would_ be received if it was coming from the client,
rather than being faked up here.
The address argument is a dotted-quad IP addresses and mandatory.
The MAC address is colon separated hex, and is mandatory. It may be
prefixed by an address-type byte followed by -, eg
10-11:22:33:44:55:66
but if the address-type byte is missing it is assumed to be 1, the type
for ethernet. This encoding is the one used in dnsmasq lease files.
The client-id is optional. If it is "*" then it treated as being missing.
*/
#include <sys/types.h>
#include <netinet/in.h>
#include <net/if.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <net/if_arp.h>
#include <sys/ioctl.h>
#include <linux/types.h>
#include <linux/netlink.h>
#include <linux/rtnetlink.h>
#include <errno.h>
#define DHCP_CHADDR_MAX 16
#define BOOTREQUEST 1
#define DHCP_COOKIE 0x63825363
#define OPTION_SERVER_IDENTIFIER 54
#define OPTION_CLIENT_ID 61
#define OPTION_MESSAGE_TYPE 53
#define OPTION_END 255
#define DHCPRELEASE 7
#define DHCP_SERVER_PORT 67
typedef unsigned char u8;
typedef unsigned short u16;
typedef unsigned int u32;
struct dhcp_packet {
u8 op, htype, hlen, hops;
u32 xid;
u16 secs, flags;
struct in_addr ciaddr, yiaddr, siaddr, giaddr;
u8 chaddr[DHCP_CHADDR_MAX], sname[64], file[128];
u32 cookie;
unsigned char options[308];
};
static struct iovec iov;
static int expand_buf(struct iovec *iov, size_t size)
{
void *new;
if (size <= iov->iov_len)
return 1;
if (!(new = malloc(size)))
{
errno = ENOMEM;
return 0;
}
if (iov->iov_base)
{
memcpy(new, iov->iov_base, iov->iov_len);
free(iov->iov_base);
}
iov->iov_base = new;
iov->iov_len = size;
return 1;
}
static ssize_t netlink_recv(int fd)
{
struct msghdr msg;
ssize_t rc;
msg.msg_control = NULL;
msg.msg_controllen = 0;
msg.msg_name = NULL;
msg.msg_namelen = 0;
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
while (1)
{
msg.msg_flags = 0;
while ((rc = recvmsg(fd, &msg, MSG_PEEK)) == -1 && errno == EINTR);
/* 2.2.x doesn't suport MSG_PEEK at all, returning EOPNOTSUPP, so we just grab a
big buffer and pray in that case. */
if (rc == -1 && errno == EOPNOTSUPP)
{
if (!expand_buf(&iov, 2000))
return -1;
break;
}
if (rc == -1 || !(msg.msg_flags & MSG_TRUNC))
break;
if (!expand_buf(&iov, iov.iov_len + 100))
return -1;
}
/* finally, read it for real */
while ((rc = recvmsg(fd, &msg, 0)) == -1 && errno == EINTR);
return rc;
}
static int parse_hex(char *in, unsigned char *out, int maxlen, int *mac_type)
{
int i = 0;
char *r;
if (mac_type)
*mac_type = 0;
while (maxlen == -1 || i < maxlen)
{
for (r = in; *r != 0 && *r != ':' && *r != '-'; r++);
if (*r == 0)
maxlen = i;
if (r != in )
{
if (*r == '-' && i == 0 && mac_type)
{
*r = 0;
*mac_type = strtol(in, NULL, 16);
mac_type = NULL;
}
else
{
*r = 0;
out[i] = strtol(in, NULL, 16);
i++;
}
}
in = r+1;
}
return i;
}
static int is_same_net(struct in_addr a, struct in_addr b, struct in_addr mask)
{
return (a.s_addr & mask.s_addr) == (b.s_addr & mask.s_addr);
}
static struct in_addr find_interface(struct in_addr client, int fd, int index)
{
struct sockaddr_nl addr;
struct nlmsghdr *h;
ssize_t len;
struct {
struct nlmsghdr nlh;
struct rtgenmsg g;
} req;
addr.nl_family = AF_NETLINK;
addr.nl_pad = 0;
addr.nl_groups = 0;
addr.nl_pid = 0; /* address to kernel */
req.nlh.nlmsg_len = sizeof(req);
req.nlh.nlmsg_type = RTM_GETADDR;
req.nlh.nlmsg_flags = NLM_F_ROOT | NLM_F_MATCH | NLM_F_REQUEST | NLM_F_ACK;
req.nlh.nlmsg_pid = 0;
req.nlh.nlmsg_seq = 1;
req.g.rtgen_family = AF_INET;
if (sendto(fd, (void *)&req, sizeof(req), 0,
(struct sockaddr *)&addr, sizeof(addr)) == -1)
{
perror("sendto failed");
exit(1);
}
while (1)
{
if ((len = netlink_recv(fd)) == -1)
{
perror("netlink");
exit(1);
}
for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
if (h->nlmsg_type == NLMSG_DONE)
exit(0);
else if (h->nlmsg_type == RTM_NEWADDR)
{
struct ifaddrmsg *ifa = NLMSG_DATA(h);
struct rtattr *rta;
unsigned int len1 = h->nlmsg_len - NLMSG_LENGTH(sizeof(*ifa));
if (ifa->ifa_index == index && ifa->ifa_family == AF_INET)
{
struct in_addr netmask, addr;
netmask.s_addr = htonl(0xffffffff << (32 - ifa->ifa_prefixlen));
addr.s_addr = 0;
for (rta = IFA_RTA(ifa); RTA_OK(rta, len1); rta = RTA_NEXT(rta, len1))
if (rta->rta_type == IFA_LOCAL)
addr = *((struct in_addr *)(rta+1));
if (addr.s_addr && is_same_net(addr, client, netmask))
return addr;
}
}
}
exit(0);
}
int main(int argc, char **argv)
{
struct in_addr server, lease;
int mac_type;
struct dhcp_packet packet;
unsigned char *p = packet.options;
struct sockaddr_in dest;
struct ifreq ifr;
int fd = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
int nl = socket(AF_NETLINK, SOCK_RAW, NETLINK_ROUTE);
struct iovec iov;
iov.iov_len = 200;
iov.iov_base = malloc(iov.iov_len);
if (argc < 4 || argc > 5)
{
fprintf(stderr, "usage: dhcp_release <interface> <addr> <mac> [<client_id>]\n");
exit(1);
}
if (fd == -1 || nl == -1)
{
perror("cannot create socket");
exit(1);
}
/* This voodoo fakes up a packet coming from the correct interface, which really matters for
a DHCP server */
strcpy(ifr.ifr_name, argv[1]);
if (setsockopt(fd, SOL_SOCKET, SO_BINDTODEVICE, &ifr, sizeof(ifr)) == -1)
{
perror("cannot setup interface");
exit(1);
}
lease.s_addr = inet_addr(argv[2]);
server = find_interface(lease, nl, if_nametoindex(argv[1]));
memset(&packet, 0, sizeof(packet));
packet.hlen = parse_hex(argv[3], packet.chaddr, DHCP_CHADDR_MAX, &mac_type);
if (mac_type == 0)
packet.htype = ARPHRD_ETHER;
else
packet.htype = mac_type;
packet.op = BOOTREQUEST;
packet.ciaddr = lease;
packet.cookie = htonl(DHCP_COOKIE);
*(p++) = OPTION_MESSAGE_TYPE;
*(p++) = 1;
*(p++) = DHCPRELEASE;
*(p++) = OPTION_SERVER_IDENTIFIER;
*(p++) = sizeof(server);
memcpy(p, &server, sizeof(server));
p += sizeof(server);
if (argc == 5 && strcmp(argv[4], "*") != 0)
{
unsigned int clid_len = parse_hex(argv[4], p+2, 255, NULL);
*(p++) = OPTION_CLIENT_ID;
*(p++) = clid_len;
p += clid_len;
}
*(p++) = OPTION_END;
dest.sin_family = AF_INET;
dest.sin_port = ntohs(DHCP_SERVER_PORT);
dest.sin_addr = server;
if (sendto(fd, &packet, sizeof(packet), 0,
(struct sockaddr *)&dest, sizeof(dest)) == -1)
{
perror("sendto failed");
exit(1);
}
return 0;
}