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-rw-r--r--src/libsystemd-network/arp-util.c140
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;
+}