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
   9 #include <linux/filter.h>
  10 #include <arpa/inet.h>
  11
  12 #include "arp-util.h"
  13 #include "fd-util.h"
  14 #include "unaligned.h"
  15 #include "util.h"
  16
  17 int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
  18         struct sock_filter filter[] = {
  19                 BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0),                                         /* A <- packet length */
  20                 BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0),           /* packet >= arp packet ? */
  21                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  22                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
  23                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),                       /* header == ethernet ? */
  24                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  25                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
  26                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),                       /* protocol == IP ? */
  27                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  28                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
  29                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0),          /* length == sizeof(ether_addr)? */
  30                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  31                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
  32                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0),             /* length == sizeof(in_addr) ? */
  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_op)),  /* A <- operation */
  35                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),                      /* protocol == request ? */
  36                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),                        /* protocol == reply ? */
  37                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  38                 /* Sender Hardware Address must be different from our own */
  39                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be32(&eth_mac->ether_addr_octet[0])),/* A <- 4 bytes of client's MAC */
  40                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  41                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)),       /* A <- 4 bytes of SHA */
  42                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  43                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6),                                  /* A == 0 ? */
  44                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be16(&eth_mac->ether_addr_octet[4])),/* A <- remainder of client's MAC */
  45                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  46                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4),   /* A <- remainder of SHA */
  47                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  48                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  49                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  50                 /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */
  51                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  52                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  53                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)),       /* A <- SPA */
  54                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  55                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  56                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  57                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  58                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  59                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)),       /* A <- TPA */
  60                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  61                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  62                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  63                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  64         };
  65         struct sock_fprog fprog = {
  66                 .len = ELEMENTSOF(filter),
  67                 .filter = (struct sock_filter*) filter
  68         };
  69         union sockaddr_union link = {
  70                 .ll.sll_family = AF_PACKET,
  71                 .ll.sll_protocol = htobe16(ETH_P_ARP),
  72                 .ll.sll_ifindex = ifindex,
  73                 .ll.sll_halen = ETH_ALEN,
  74                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
  75         };
  76         _cleanup_close_ int s = -1;
  77         int r;
  78
  79         assert(ifindex > 0);
  80
  81         s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
  82         if (s < 0)
  83                 return -errno;
  84
  85         r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
  86         if (r < 0)
  87                 return -errno;
  88
  89         r = bind(s, &link.sa, sizeof(link.ll));
  90         if (r < 0)
  91                 return -errno;
  92
  93         return TAKE_FD(s);
  94 }
  95
  96 static int arp_send_packet(int fd, int ifindex,
  97                            be32_t pa, const struct ether_addr *ha,
  98                            bool announce) {
  99         union sockaddr_union link = {
 100                 .ll.sll_family = AF_PACKET,
 101                 .ll.sll_protocol = htobe16(ETH_P_ARP),
 102                 .ll.sll_ifindex = ifindex,
 103                 .ll.sll_halen = ETH_ALEN,
 104                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
 105         };
 106         struct ether_arp arp = {
 107                 .ea_hdr.ar_hrd = htobe16(ARPHRD_ETHER), /* HTYPE */
 108                 .ea_hdr.ar_pro = htobe16(ETHERTYPE_IP), /* PTYPE */
 109                 .ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
 110                 .ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
 111                 .ea_hdr.ar_op = htobe16(ARPOP_REQUEST), /* REQUEST */
 112         };
 113         int r;
 114
 115         assert(fd >= 0);
 116         assert(pa != 0);
 117         assert(ha);
 118
 119         memcpy(&arp.arp_sha, ha, ETH_ALEN);
 120         memcpy(&arp.arp_tpa, &pa, sizeof(pa));
 121
 122         if (announce)
 123                 memcpy(&arp.arp_spa, &pa, sizeof(pa));
 124
 125         r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
 126         if (r < 0)
 127                 return -errno;
 128
 129         return 0;
 130 }
 131
 132 int arp_send_probe(int fd, int ifindex,
 133                     be32_t pa, const struct ether_addr *ha) {
 134         return arp_send_packet(fd, ifindex, pa, ha, false);
 135 }
 136
 137 int arp_send_announcement(int fd, int ifindex,
 138                           be32_t pa, const struct ether_addr *ha) {
 139         return arp_send_packet(fd, ifindex, pa, ha, true);
 140 }