src/libsystemd-network/arp-util.c

   1 /***
   2   This file is part of systemd.
   3
   4   Copyright (C) 2014 Axis Communications AB. All rights reserved.
   5   Copyright (C) 2015 Tom Gundersen
   6
   7   systemd is free software; you can redistribute it and/or modify it
   8   under the terms of the GNU Lesser General Public License as published by
   9   the Free Software Foundation; either version 2.1 of the License, or
  10   (at your option) any later version.
  11
  12   systemd is distributed in the hope that it will be useful, but
  13   WITHOUT ANY WARRANTY; without even the implied warranty of
  14   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  15   Lesser General Public License for more details.
  16
  17   You should have received a copy of the GNU Lesser General Public License
  18   along with systemd; If not, see <http://www.gnu.org/licenses/>.
  19 ***/
  20
  21 #include <linux/filter.h>
  22 #include <arpa/inet.h>
  23
  24 #include "arp-util.h"
  25 #include "fd-util.h"
  26 #include "util.h"
  27
  28 int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
  29         struct sock_filter filter[] = {
  30                 BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0),                                         /* A <- packet length */
  31                 BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0),           /* packet >= arp packet ? */
  32                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  33                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
  34                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),                       /* header == ethernet ? */
  35                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  36                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
  37                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),                       /* protocol == IP ? */
  38                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  39                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
  40                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0),          /* length == sizeof(ether_addr)? */
  41                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  42                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
  43                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0),             /* length == sizeof(in_addr) ? */
  44                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  45                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_op)),  /* A <- operation */
  46                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),                      /* protocol == request ? */
  47                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),                        /* protocol == reply ? */
  48                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  49                 /* Sender Hardware Address must be different from our own */
  50                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(*((uint32_t *) eth_mac))),                  /* A <- 4 bytes of client's MAC */
  51                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  52                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)),       /* A <- 4 bytes of SHA */
  53                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  54                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6),                                  /* A == 0 ? */
  55                 BPF_STMT(BPF_LD + BPF_IMM, htobe16(*((uint16_t *) (((char *) eth_mac) + 4)))), /* A <- remainder of client's MAC */
  56                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  57                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4),   /* A <- remainder of SHA */
  58                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  59                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  60                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  61                 /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about*/
  62                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  63                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  64                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)),       /* A <- SPA */
  65                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  66                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  67                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  68                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  69                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  70                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)),       /* A <- TPA */
  71                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  72                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  73                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  74                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  75         };
  76         struct sock_fprog fprog = {
  77                 .len = ELEMENTSOF(filter),
  78                 .filter = (struct sock_filter*) filter
  79         };
  80         union sockaddr_union link = {
  81                 .ll.sll_family = AF_PACKET,
  82                 .ll.sll_protocol = htons(ETH_P_ARP),
  83                 .ll.sll_ifindex = ifindex,
  84                 .ll.sll_halen = ETH_ALEN,
  85                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
  86         };
  87         _cleanup_close_ int s = -1;
  88         int r;
  89
  90         assert(ifindex > 0);
  91
  92         s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
  93         if (s < 0)
  94                 return -errno;
  95
  96         r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
  97         if (r < 0)
  98                 return -errno;
  99
 100         r = bind(s, &link.sa, sizeof(link.ll));
 101         if (r < 0)
 102                 return -errno;
 103
 104         r = s;
 105         s = -1;
 106
 107         return r;
 108 }
 109
 110 static int arp_send_packet(int fd, int ifindex,
 111                            be32_t pa, const struct ether_addr *ha,
 112                            bool announce) {
 113         union sockaddr_union link = {
 114                 .ll.sll_family = AF_PACKET,
 115                 .ll.sll_protocol = htons(ETH_P_ARP),
 116                 .ll.sll_ifindex = ifindex,
 117                 .ll.sll_halen = ETH_ALEN,
 118                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
 119         };
 120         struct ether_arp arp = {
 121                 .ea_hdr.ar_hrd = htons(ARPHRD_ETHER), /* HTYPE */
 122                 .ea_hdr.ar_pro = htons(ETHERTYPE_IP), /* PTYPE */
 123                 .ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
 124                 .ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
 125                 .ea_hdr.ar_op = htons(ARPOP_REQUEST), /* REQUEST */
 126         };
 127         int r;
 128
 129         assert(fd >= 0);
 130         assert(pa != 0);
 131         assert(ha);
 132
 133         memcpy(&arp.arp_sha, ha, ETH_ALEN);
 134         memcpy(&arp.arp_tpa, &pa, sizeof(pa));
 135
 136         if (announce)
 137                 memcpy(&arp.arp_spa, &pa, sizeof(pa));
 138
 139         r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
 140         if (r < 0)
 141                 return -errno;
 142
 143         return 0;
 144 }
 145
 146 int arp_send_probe(int fd, int ifindex,
 147                     be32_t pa, const struct ether_addr *ha) {
 148         return arp_send_packet(fd, ifindex, pa, ha, false);
 149 }
 150
 151 int arp_send_announcement(int fd, int ifindex,
 152                           be32_t pa, const struct ether_addr *ha) {
 153         return arp_send_packet(fd, ifindex, pa, ha, true);
 154 }