diff options
Diffstat (limited to 'src/libsystemd-network/arp-util.c')
| -rw-r--r-- | src/libsystemd-network/arp-util.c | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/src/libsystemd-network/arp-util.c b/src/libsystemd-network/arp-util.c new file mode 100644 index 0000000..99a5f69 --- /dev/null +++ b/src/libsystemd-network/arp-util.c @@ -0,0 +1,140 @@ +/* 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" +#include "util.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 = -1; + 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; +} |