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 "util.h"
  28
  29 int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
  30         struct sock_filter filter[] = {
  31                 BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0),                                         /* A <- packet length */
  32                 BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0),           /* packet >= arp packet ? */
  33                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  34                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
  35                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),                       /* header == ethernet ? */
  36                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  37                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
  38                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),                       /* protocol == IP ? */
  39                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  40                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
  41                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0),          /* length == sizeof(ether_addr)? */
  42                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  43                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
  44                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0),             /* length == sizeof(in_addr) ? */
  45                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  46                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_op)),  /* A <- operation */
  47                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),                      /* protocol == request ? */
  48                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),                        /* protocol == reply ? */
  49                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  50                 /* Sender Hardware Address must be different from our own */
  51                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(*((uint32_t *) eth_mac))),                  /* A <- 4 bytes of client's MAC */
  52                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  53                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)),       /* A <- 4 bytes of SHA */
  54                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  55                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6),                                  /* A == 0 ? */
  56                 BPF_STMT(BPF_LD + BPF_IMM, htobe16(*((uint16_t *) (((char *) eth_mac) + 4)))), /* A <- remainder of client's MAC */
  57                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  58                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4),   /* A <- remainder of SHA */
  59                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  60                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  61                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  62                 /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */
  63                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  64                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  65                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)),       /* A <- SPA */
  66                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  67                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  68                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  69                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  70                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  71                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)),       /* A <- TPA */
  72                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  73                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  74                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  75                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  76         };
  77         struct sock_fprog fprog = {
  78                 .len = ELEMENTSOF(filter),
  79                 .filter = (struct sock_filter*) filter
  80         };
  81         union sockaddr_union link = {
  82                 .ll.sll_family = AF_PACKET,
  83                 .ll.sll_protocol = htobe16(ETH_P_ARP),
  84                 .ll.sll_ifindex = ifindex,
  85                 .ll.sll_halen = ETH_ALEN,
  86                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
  87         };
  88         _cleanup_close_ int s = -1;
  89         int r;
  90
  91         assert(ifindex > 0);
  92
  93         s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
  94         if (s < 0)
  95                 return -errno;
  96
  97         r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
  98         if (r < 0)
  99                 return -errno;
 100
 101         r = bind(s, &link.sa, sizeof(link.ll));
 102         if (r < 0)
 103                 return -errno;
 104
 105         r = s;
 106         s = -1;
 107
 108         return r;
 109 }
 110
 111 static int arp_send_packet(int fd, int ifindex,
 112                            be32_t pa, const struct ether_addr *ha,
 113                            bool announce) {
 114         union sockaddr_union link = {
 115                 .ll.sll_family = AF_PACKET,
 116                 .ll.sll_protocol = htobe16(ETH_P_ARP),
 117                 .ll.sll_ifindex = ifindex,
 118                 .ll.sll_halen = ETH_ALEN,
 119                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
 120         };
 121         struct ether_arp arp = {
 122                 .ea_hdr.ar_hrd = htobe16(ARPHRD_ETHER), /* HTYPE */
 123                 .ea_hdr.ar_pro = htobe16(ETHERTYPE_IP), /* PTYPE */
 124                 .ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
 125                 .ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
 126                 .ea_hdr.ar_op = htobe16(ARPOP_REQUEST), /* REQUEST */
 127         };
 128         int r;
 129
 130         assert(fd >= 0);
 131         assert(pa != 0);
 132         assert(ha);
 133
 134         memcpy(&arp.arp_sha, ha, ETH_ALEN);
 135         memcpy(&arp.arp_tpa, &pa, sizeof(pa));
 136
 137         if (announce)
 138                 memcpy(&arp.arp_spa, &pa, sizeof(pa));
 139
 140         r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
 141         if (r < 0)
 142                 return -errno;
 143
 144         return 0;
 145 }
 146
 147 int arp_send_probe(int fd, int ifindex,
 148                     be32_t pa, const struct ether_addr *ha) {
 149         return arp_send_packet(fd, ifindex, pa, ha, false);
 150 }
 151
 152 int arp_send_announcement(int fd, int ifindex,
 153                           be32_t pa, const struct ether_addr *ha) {
 154         return arp_send_packet(fd, ifindex, pa, ha, true);
 155 }