src/libsystemd-network/arp-util.c

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2 /***
   3   Copyright (C) 2014 Axis Communications AB. All rights reserved.
   4   Copyright (C) 2015 Tom Gundersen
   5 ***/
   6
   7 #include <linux/filter.h>
   8 #include <arpa/inet.h>
   9
  10 #include "arp-util.h"
  11 #include "fd-util.h"
  12 #include "unaligned.h"
  13 #include "util.h"
  14
  15 int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_addr *eth_mac) {
  16         struct sock_filter filter[] = {
  17                 BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0),                                         /* A <- packet length */
  18                 BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0),           /* packet >= arp packet ? */
  19                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  20                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hrd)), /* A <- header */
  21                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPHRD_ETHER, 1, 0),                       /* header == ethernet ? */
  22                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  23                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pro)), /* A <- protocol */
  24                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETHERTYPE_IP, 1, 0),                       /* protocol == IP ? */
  25                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  26                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_hln)), /* A <- hardware address length */
  27                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct ether_addr), 1, 0),          /* length == sizeof(ether_addr)? */
  28                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  29                 BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_pln)), /* A <- protocol address length */
  30                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, sizeof(struct in_addr), 1, 0),             /* length == sizeof(in_addr) ? */
  31                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  32                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, ea_hdr.ar_op)),  /* A <- operation */
  33                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REQUEST, 2, 0),                      /* protocol == request ? */
  34                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0),                        /* protocol == reply ? */
  35                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  36                 /* Sender Hardware Address must be different from our own */
  37                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be32(&eth_mac->ether_addr_octet[0])),/* A <- 4 bytes of client's MAC */
  38                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  39                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)),       /* A <- 4 bytes of SHA */
  40                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  41                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6),                                  /* A == 0 ? */
  42                 BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be16(&eth_mac->ether_addr_octet[4])),/* A <- remainder of client's MAC */
  43                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  44                 BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4),   /* A <- remainder of SHA */
  45                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* A xor X */
  46                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  47                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  48                 /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */
  49                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  50                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  51                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)),       /* A <- SPA */
  52                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  53                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  54                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  55                 BPF_STMT(BPF_LD + BPF_IMM, htobe32(address)),                                  /* A <- clients IP */
  56                 BPF_STMT(BPF_MISC + BPF_TAX, 0),                                               /* X <- A */
  57                 BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)),       /* A <- TPA */
  58                 BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0),                                        /* X xor A */
  59                 BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1),                                  /* A == 0 ? */
  60                 BPF_STMT(BPF_RET + BPF_K, 65535),                                              /* return all */
  61                 BPF_STMT(BPF_RET + BPF_K, 0),                                                  /* ignore */
  62         };
  63         struct sock_fprog fprog = {
  64                 .len = ELEMENTSOF(filter),
  65                 .filter = (struct sock_filter*) filter
  66         };
  67         union sockaddr_union link = {
  68                 .ll.sll_family = AF_PACKET,
  69                 .ll.sll_protocol = htobe16(ETH_P_ARP),
  70                 .ll.sll_ifindex = ifindex,
  71                 .ll.sll_halen = ETH_ALEN,
  72                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
  73         };
  74         _cleanup_close_ int s = -1;
  75         int r;
  76
  77         assert(ifindex > 0);
  78
  79         s = socket(PF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
  80         if (s < 0)
  81                 return -errno;
  82
  83         r = setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog));
  84         if (r < 0)
  85                 return -errno;
  86
  87         r = bind(s, &link.sa, sizeof(link.ll));
  88         if (r < 0)
  89                 return -errno;
  90
  91         return TAKE_FD(s);
  92 }
  93
  94 static int arp_send_packet(int fd, int ifindex,
  95                            be32_t pa, const struct ether_addr *ha,
  96                            bool announce) {
  97         union sockaddr_union link = {
  98                 .ll.sll_family = AF_PACKET,
  99                 .ll.sll_protocol = htobe16(ETH_P_ARP),
 100                 .ll.sll_ifindex = ifindex,
 101                 .ll.sll_halen = ETH_ALEN,
 102                 .ll.sll_addr = { 0xff, 0xff, 0xff, 0xff, 0xff, 0xff },
 103         };
 104         struct ether_arp arp = {
 105                 .ea_hdr.ar_hrd = htobe16(ARPHRD_ETHER), /* HTYPE */
 106                 .ea_hdr.ar_pro = htobe16(ETHERTYPE_IP), /* PTYPE */
 107                 .ea_hdr.ar_hln = ETH_ALEN, /* HLEN */
 108                 .ea_hdr.ar_pln = sizeof(be32_t), /* PLEN */
 109                 .ea_hdr.ar_op = htobe16(ARPOP_REQUEST), /* REQUEST */
 110         };
 111         int r;
 112
 113         assert(fd >= 0);
 114         assert(pa != 0);
 115         assert(ha);
 116
 117         memcpy(&arp.arp_sha, ha, ETH_ALEN);
 118         memcpy(&arp.arp_tpa, &pa, sizeof(pa));
 119
 120         if (announce)
 121                 memcpy(&arp.arp_spa, &pa, sizeof(pa));
 122
 123         r = sendto(fd, &arp, sizeof(struct ether_arp), 0, &link.sa, sizeof(link.ll));
 124         if (r < 0)
 125                 return -errno;
 126
 127         return 0;
 128 }
 129
 130 int arp_send_probe(int fd, int ifindex,
 131                     be32_t pa, const struct ether_addr *ha) {
 132         return arp_send_packet(fd, ifindex, pa, ha, false);
 133 }
 134
 135 int arp_send_announcement(int fd, int ifindex,
 136                           be32_t pa, const struct ether_addr *ha) {
 137         return arp_send_packet(fd, ifindex, pa, ha, true);
 138 }