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/* SPDX-License-Identifier: LGPL-2.1-or-later */
/***
Copyright © 2014 Axis Communications AB. All rights reserved.
***/
#include <arpa/inet.h>
#include <linux/filter.h>
#include <netinet/if_ether.h>
#include "arp-util.h"
#include "ether-addr-util.h"
#include "fd-util.h"
#include "in-addr-util.h"
#include "unaligned.h"
int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *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_LDX + BPF_IMM, unaligned_read_be32(&mac->ether_addr_octet[0])), /* X <- 4 bytes of client's MAC */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)), /* A <- 4 bytes of SHA */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 4), /* A == X ? */
BPF_STMT(BPF_LDX + BPF_IMM, unaligned_read_be16(&mac->ether_addr_octet[4])), /* X <- remainder of client's MAC */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4), /* A <- remainder of SHA */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == X ? */
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_LDX + BPF_IMM, htobe32(a->s_addr)), /* X <- clients IP */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)), /* A <- SPA */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == X ? */
BPF_STMT(BPF_RET + BPF_K, UINT32_MAX), /* accept */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)), /* A <- TPA */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, UINT32_MAX), /* accept */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
};
struct sock_fprog fprog = {
.len = ELEMENTSOF(filter),
.filter = (struct sock_filter*) filter,
};
assert(fd >= 0);
if (setsockopt(fd, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog)) < 0)
return -errno;
return 0;
}
int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const struct ether_addr *mac) {
union sockaddr_union link = {
.ll.sll_family = AF_PACKET,
.ll.sll_protocol = htobe16(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 = -EBADF;
int r;
assert(ifindex > 0);
assert(mac);
s = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
if (s < 0)
return -errno;
r = arp_update_filter(s, a, mac);
if (r < 0)
return r;
if (bind(s, &link.sa, sizeof(link.ll)) < 0)
return -errno;
return TAKE_FD(s);
}
int arp_send_packet(
int fd,
int ifindex,
const struct in_addr *pa,
const struct ether_addr *ha,
bool announce) {
union sockaddr_union link = {
.ll.sll_family = AF_PACKET,
.ll.sll_protocol = htobe16(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 = htobe16(ARPHRD_ETHER), /* HTYPE */
.ea_hdr.ar_pro = htobe16(ETHERTYPE_IP), /* PTYPE */
.ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
.ea_hdr.ar_pln = sizeof(struct in_addr), /* PLEN */
.ea_hdr.ar_op = htobe16(ARPOP_REQUEST), /* REQUEST */
};
ssize_t n;
assert(fd >= 0);
assert(ifindex > 0);
assert(pa);
assert(in4_addr_is_set(pa));
assert(ha);
assert(!ether_addr_is_null(ha));
memcpy(&arp.arp_sha, ha, ETH_ALEN);
memcpy(&arp.arp_tpa, pa, sizeof(struct in_addr));
if (announce)
memcpy(&arp.arp_spa, pa, sizeof(struct in_addr));
n = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
if (n < 0)
return -errno;
if (n != sizeof(struct ether_arp))
return -EIO;
return 0;
}
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