src/libsystemd-network/arp-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   This file is part of systemd.
   4
   5   Copyright (C) 2014 Axis Communications AB. All rights reserved.
   6   Copyright (C) 2015 Tom Gundersen
   7
   8   systemd is free software; you can redistribute it and/or modify it
   9   under the terms of the GNU Lesser General Public License as published by
  10   the Free Software Foundation; either version 2.1 of the License, or
  11   (at your option) any later version.
  12
  13   systemd is distributed in the hope that it will be useful, but
  14   WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  16   Lesser General Public License for more details.
  17
  18   You should have received a copy of the GNU Lesser General Public License
  19   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  20 ***/
  21
  22 #include <linux/filter.h>
  23 #include <arpa/inet.h>
  24
  25 #include "arp-util.h"
  26 #include "fd-util.h"
  27 #include "unaligned.h"
  28 #include "util.h"
  29
  30 int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
  31         struct sock_filter filter[] = {
  32                 BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0),                                         /* A <- packet length */
  33                 BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0),           /* packet >= arp packet ? */
  34                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  35                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
  36                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),                       /* header == ethernet ? */
  37                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  38                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
  39                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),                       /* protocol == IP ? */
  40                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  41                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
  42                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0),          /* length == sizeof(ether_addr)? */
  43                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  44                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
  45                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0),             /* length == sizeof(in_addr) ? */
  46                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  47                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_op)),  /* A <- operation */
  48                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),                      /* protocol == request ? */
  49                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),                        /* protocol == reply ? */
  50                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  51                 /* Sender Hardware Address must be different from our own */
  52                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be32(&eth_mac->ether_addr_octet[0])),/* A <- 4 bytes of client's MAC */
  53                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  54                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)),       /* A <- 4 bytes of SHA */
  55                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  56                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6),                                  /* A == 0 ? */
  57                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be16(&eth_mac->ether_addr_octet[4])),/* A <- remainder of client's MAC */
  58                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  59                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4),   /* A <- remainder of SHA */
  60                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  61                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  62                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  63                 /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */
  64                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  65                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  66                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)),       /* A <- SPA */
  67                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  68                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  69                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  70                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  71                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  72                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)),       /* A <- TPA */
  73                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  74                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  75                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  76                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  77         };
  78         struct sock_fprog fprog = {
  79                 .len = ELEMENTSOF(filter),
  80                 .filter = (struct sock_filter*) filter
  81         };
  82         union sockaddr_union link = {
  83                 .ll.sll_family = AF_PACKET,
  84                 .ll.sll_protocol = htobe16(ETH_P_ARP),
  85                 .ll.sll_ifindex = ifindex,
  86                 .ll.sll_halen = ETH_ALEN,
  87                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
  88         };
  89         _cleanup_close_ int s = -1;
  90         int r;
  91
  92         assert(ifindex > 0);
  93
  94         s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
  95         if (s < 0)
  96                 return -errno;
  97
  98         r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
  99         if (r < 0)
 100                 return -errno;
 101
 102         r = bind(s, &link.sa, sizeof(link.ll));
 103         if (r < 0)
 104                 return -errno;
 105
 106         r = s;
 107         s = -1;
 108
 109         return r;
 110 }
 111
 112 static int arp_send_packet(int fd, int ifindex,
 113                            be32_t pa, const struct ether_addr *ha,
 114                            bool announce) {
 115         union sockaddr_union link = {
 116                 .ll.sll_family = AF_PACKET,
 117                 .ll.sll_protocol = htobe16(ETH_P_ARP),
 118                 .ll.sll_ifindex = ifindex,
 119                 .ll.sll_halen = ETH_ALEN,
 120                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
 121         };
 122         struct ether_arp arp = {
 123                 .ea_hdr.ar_hrd = htobe16(ARPHRD_ETHER), /* HTYPE */
 124                 .ea_hdr.ar_pro = htobe16(ETHERTYPE_IP), /* PTYPE */
 125                 .ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
 126                 .ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
 127                 .ea_hdr.ar_op = htobe16(ARPOP_REQUEST), /* REQUEST */
 128         };
 129         int r;
 130
 131         assert(fd >= 0);
 132         assert(pa != 0);
 133         assert(ha);
 134
 135         memcpy(&arp.arp_sha, ha, ETH_ALEN);
 136         memcpy(&arp.arp_tpa, &pa, sizeof(pa));
 137
 138         if (announce)
 139                 memcpy(&arp.arp_spa, &pa, sizeof(pa));
 140
 141         r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
 142         if (r < 0)
 143                 return -errno;
 144
 145         return 0;
 146 }
 147
 148 int arp_send_probe(int fd, int ifindex,
 149                     be32_t pa, const struct ether_addr *ha) {
 150         return arp_send_packet(fd, ifindex, pa, ha, false);
 151 }
 152
 153 int arp_send_announcement(int fd, int ifindex,
 154                           be32_t pa, const struct ether_addr *ha) {
 155         return arp_send_packet(fd, ifindex, pa, ha, true);
 156 }