arp-util.c revision 996d16975b4d802335188a3be2bbc3635c1287f3
/***
This file is part of systemd.
Copyright (C) 2014 Axis Communications AB. All rights reserved.
Copyright (C) 2015 Tom Gundersen
systemd is free software; you can redistribute it and/or modify it
under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation; either version 2.1 of the License, or
(at your option) any later version.
systemd 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
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public License
along with systemd; If not, see <http://www.gnu.org/licenses/>.
***/
#include <linux/filter.h>
#include <arpa/inet.h>
#include "util.h"
#include "arp-util.h"
int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
struct sock_filter filter[] = {
BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0), /* A <- packet length */
BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0), /* packet >= arp packet ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0), /* header == ethernet ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0), /* protocol == IP ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0), /* length == sizeof(ether_addr)? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0), /* length == sizeof(in_addr) ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_op)), /* A <- operation */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0), /* protocol == request ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0), /* protocol == reply ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
/* Sender Hardware Address must be different from our own */
BPF_STMT(BPF_LD + BPF_IMM, htobe32(*((uint32_t *) eth_mac))), /* A <- 4 bytes of client's MAC */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)), /* A <- 4 bytes of SHA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6), /* A == 0 ? */
BPF_STMT(BPF_LD + BPF_IMM, htobe16(*((uint16_t *) (((char *) eth_mac) + 4)))), /* A <- remainder of client's MAC */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4), /* A <- remainder of SHA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
/* Sender Protocol Address or Target Protocol Address must be equal to the one we care about*/
BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)), /* A <- clients IP */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)), /* A <- SPA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* X xor A */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */
BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)), /* A <- clients IP */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)), /* A <- TPA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* X xor A */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
};
struct sock_fprog fprog = {
.len = ELEMENTSOF(filter),
.filter = (struct sock_filter*) filter
};
union sockaddr_union link = {
.ll.sll_family = AF_PACKET,
.ll.sll_protocol = htons(ETH_P_ARP),
.ll.sll_ifindex = ifindex,
.ll.sll_halen = ETH_ALEN,
.ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
};
_cleanup_close_ int s = -1;
int r;
assert(ifindex > 0);
s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
if (s < 0)
return -errno;
r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
if (r < 0)
return -errno;
r = bind(s, &link.sa, sizeof(link.ll));
if (r < 0)
return -errno;
r = s;
s = -1;
return r;
}
static int arp_send_packet(int fd, int ifindex,
be32_t pa, const struct ether_addr *ha,
bool announce) {
union sockaddr_union link = {
.ll.sll_family = AF_PACKET,
.ll.sll_protocol = htons(ETH_P_ARP),
.ll.sll_ifindex = ifindex,
.ll.sll_halen = ETH_ALEN,
.ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
};
struct ether_arp arp = {
.ea_hdr.ar_hrd = htons(ARPHRD_ETHER), /* HTYPE */
.ea_hdr.ar_pro = htons(ETHERTYPE_IP), /* PTYPE */
.ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
.ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
.ea_hdr.ar_op = htons(ARPOP_REQUEST), /* REQUEST */
};
int r;
assert(fd >= 0);
assert(pa != 0);
assert(ha);
memcpy(&arp.arp_sha, ha, ETH_ALEN);
memcpy(&arp.arp_tpa, &pa, sizeof(pa));
if (announce)
memcpy(&arp.arp_spa, &pa, sizeof(pa));
r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
if (r < 0)
return -errno;
return 0;
}
int arp_send_probe(int fd, int ifindex,
be32_t pa, const struct ether_addr *ha) {
return arp_send_packet(fd, ifindex, pa, ha, false);
}
int arp_send_announcement(int fd, int ifindex,
be32_t pa, const struct ether_addr *ha) {
return arp_send_packet(fd, ifindex, pa, ha, true);
}