/* simplistic Token Ring <-> Ethernet bridge in userspace based on AF_PACKET * * (C) 2022 by Harald Welte * for Osmocom retronetworking project. * * SPDX-License-Identifier: GPL-2.0+ * * You need to call this program with two arguments: * - first: the token ring device (e.g. 'tr0') * - second: the ethernet device (e.g. 'eth0') */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #define TR_ALEN 6 #define AC 0x10 #define LLC_FRAME 0x40 /* Copied from libosmocore.git src/bits.c */ /* look-up table for bit-reversal within a byte. Generated using: int i,k; for (i = 0 ; i < 256 ; i++) { uint8_t sample = 0 ; for (k = 0; k<8; k++) { if ( i & 1 << k ) sample |= 0x80 >> k; } flip_table[i] = sample; } */ static const uint8_t flip_table[256] = { 0x00, 0x80, 0x40, 0xc0, 0x20, 0xa0, 0x60, 0xe0, 0x10, 0x90, 0x50, 0xd0, 0x30, 0xb0, 0x70, 0xf0, 0x08, 0x88, 0x48, 0xc8, 0x28, 0xa8, 0x68, 0xe8, 0x18, 0x98, 0x58, 0xd8, 0x38, 0xb8, 0x78, 0xf8, 0x04, 0x84, 0x44, 0xc4, 0x24, 0xa4, 0x64, 0xe4, 0x14, 0x94, 0x54, 0xd4, 0x34, 0xb4, 0x74, 0xf4, 0x0c, 0x8c, 0x4c, 0xcc, 0x2c, 0xac, 0x6c, 0xec, 0x1c, 0x9c, 0x5c, 0xdc, 0x3c, 0xbc, 0x7c, 0xfc, 0x02, 0x82, 0x42, 0xc2, 0x22, 0xa2, 0x62, 0xe2, 0x12, 0x92, 0x52, 0xd2, 0x32, 0xb2, 0x72, 0xf2, 0x0a, 0x8a, 0x4a, 0xca, 0x2a, 0xaa, 0x6a, 0xea, 0x1a, 0x9a, 0x5a, 0xda, 0x3a, 0xba, 0x7a, 0xfa, 0x06, 0x86, 0x46, 0xc6, 0x26, 0xa6, 0x66, 0xe6, 0x16, 0x96, 0x56, 0xd6, 0x36, 0xb6, 0x76, 0xf6, 0x0e, 0x8e, 0x4e, 0xce, 0x2e, 0xae, 0x6e, 0xee, 0x1e, 0x9e, 0x5e, 0xde, 0x3e, 0xbe, 0x7e, 0xfe, 0x01, 0x81, 0x41, 0xc1, 0x21, 0xa1, 0x61, 0xe1, 0x11, 0x91, 0x51, 0xd1, 0x31, 0xb1, 0x71, 0xf1, 0x09, 0x89, 0x49, 0xc9, 0x29, 0xa9, 0x69, 0xe9, 0x19, 0x99, 0x59, 0xd9, 0x39, 0xb9, 0x79, 0xf9, 0x05, 0x85, 0x45, 0xc5, 0x25, 0xa5, 0x65, 0xe5, 0x15, 0x95, 0x55, 0xd5, 0x35, 0xb5, 0x75, 0xf5, 0x0d, 0x8d, 0x4d, 0xcd, 0x2d, 0xad, 0x6d, 0xed, 0x1d, 0x9d, 0x5d, 0xdd, 0x3d, 0xbd, 0x7d, 0xfd, 0x03, 0x83, 0x43, 0xc3, 0x23, 0xa3, 0x63, 0xe3, 0x13, 0x93, 0x53, 0xd3, 0x33, 0xb3, 0x73, 0xf3, 0x0b, 0x8b, 0x4b, 0xcb, 0x2b, 0xab, 0x6b, 0xeb, 0x1b, 0x9b, 0x5b, 0xdb, 0x3b, 0xbb, 0x7b, 0xfb, 0x07, 0x87, 0x47, 0xc7, 0x27, 0xa7, 0x67, 0xe7, 0x17, 0x97, 0x57, 0xd7, 0x37, 0xb7, 0x77, 0xf7, 0x0f, 0x8f, 0x4f, 0xcf, 0x2f, 0xaf, 0x6f, 0xef, 0x1f, 0x9f, 0x5f, 0xdf, 0x3f, 0xbf, 0x7f, 0xff, }; struct tr_hdr { uint8_t ac; uint8_t fc; uint8_t daddr[TR_ALEN]; uint8_t saddr[TR_ALEN]; } __attribute((packed)); struct bridge_state { struct { int socket; } tr; struct { int socket; } eth; }; void osmo_revbytebits_buf(uint8_t *buf, int len) { int i; for (i = 0; i < len; i++) buf[i] = flip_table[buf[i]]; } static int devname2ifindex(const char *ifname) { struct ifreq ifr; int sk, rc; sk = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP); if (sk < 0) return sk; memset(&ifr, 0, sizeof(ifr)); strncpy(ifr.ifr_name, ifname, sizeof(ifr.ifr_name)); ifr.ifr_name[sizeof(ifr.ifr_name)-1] = 0; rc = ioctl(sk, SIOCGIFINDEX, &ifr); close(sk); if (rc < 0) return rc; return ifr.ifr_ifindex; } static int enable_promisc(int sk, int ifindex) { struct packet_mreq mreq = {0}; int rc; mreq.mr_ifindex = ifindex; mreq.mr_type = PACKET_MR_PROMISC; rc = setsockopt(sk, SOL_PACKET, PACKET_ADD_MEMBERSHIP, &mreq, sizeof(mreq)); if (rc < 0) { fprintf(stderr, "Unable to set promiscuous mode: %s\n", strerror(errno)); return rc; } return 0; } static int open_packet_socket(int ifindex, int proto) { struct sockaddr_ll addr; int fd, rc; memset(&addr, 0, sizeof(addr)); addr.sll_family = AF_PACKET; addr.sll_protocol = htons(proto); addr.sll_ifindex = ifindex; /* we want only packets for _other_ hosts, not packets sent by us or received for us locally */ addr.sll_pkttype = PACKET_OTHERHOST; fd = socket(AF_PACKET, SOCK_RAW, htons(proto)); if (fd < 0) { fprintf(stderr, "Can not create AF_PACKET socket. Are you root or have CAP_NET_RAW?\n"); return fd; } /* there's a race condition between the above syscall and the bind() call below, * causing other packets to be received in between */ rc = bind(fd, (struct sockaddr *)&addr, sizeof(addr)); if (rc < 0) { fprintf(stderr, "Can not bind AF_PACKET socket to ifindex %d\n", ifindex); close(fd); return rc; } rc = enable_promisc(fd, ifindex); if (rc < 0) { close(fd); return rc; } return fd; } static int open_packet_socket_for_netdev(const char *ifname, int proto) { int rc; rc = devname2ifindex(ifname); if (rc < 0) { fprintf(stderr, "Cannot find net-device '%s': %s\n", ifname, strerror(errno)); return rc; } return open_packet_socket(rc, proto); } static int write_tr(int socket, const struct tr_hdr *trh, const uint8_t *payload, size_t payload_len) { struct iovec iov[2] = { { .iov_base = (void *) trh, .iov_len = sizeof(*trh), }, { .iov_base = (void *) payload, .iov_len = payload_len, } }; return writev(socket, iov, 2); } static int eth2tr(struct bridge_state *bst) { uint8_t buf[2000]; const struct ethhdr *ethh = (struct ethhdr *) buf; struct tr_hdr trh; int rc, ethlen; rc = read(bst->eth.socket, buf, sizeof(buf)); if (rc <= 0) { fprintf(stderr, "Error reading from ETH: %s\n", strerror(errno)); return rc; } ethlen = rc; if (ethlen < sizeof(*ethh)) { fprintf(stderr, "short frame from ETH\n"); return 0; } trh.ac = AC; trh.fc = LLC_FRAME; memcpy(&trh.daddr, ethh->h_dest, sizeof(trh.daddr)); osmo_revbytebits_buf(trh.daddr, TR_ALEN); memcpy(&trh.saddr, ethh->h_source, sizeof(trh.saddr)); osmo_revbytebits_buf(trh.saddr, TR_ALEN); return write_tr(bst->tr.socket, &trh, buf + sizeof(*ethh), ethlen - sizeof(*ethh)); } static int write_eth(int socket, const struct ethhdr *ethh, const uint8_t *payload, size_t payload_len) { struct iovec iov[2] = { { .iov_base = (void *) ethh, .iov_len = sizeof(*ethh), }, { .iov_base = (void *) payload, .iov_len = payload_len, } }; return writev(socket, iov, 2); } static int tr2eth(struct bridge_state *bst) { uint8_t buf[2000]; const struct tr_hdr *trh = (const struct tr_hdr *) buf; struct ethhdr ethh; int rc, trlen; rc = read(bst->tr.socket, buf, sizeof(buf)); if (rc <= 0) { fprintf(stderr, "Error reading from TR: %s\n", strerror(errno)); return rc; } trlen = rc; if (trlen < sizeof(*trh)) { fprintf(stderr, "short frame from TR\n"); return 0; } memcpy(ðh.h_dest, trh->daddr, sizeof(ethh.h_dest)); osmo_revbytebits_buf(ethh.h_dest, TR_ALEN); memcpy(ðh.h_source, trh->saddr, sizeof(ethh.h_source)); osmo_revbytebits_buf(ethh.h_source, TR_ALEN); ethh.h_proto = htons(ETH_P_802_2); return write_eth(bst->eth.socket, ðh, buf + sizeof(*trh), trlen - sizeof(*trh)); } static int bridge_main(struct bridge_state *bst) { int maxfd = 0; int rc; fd_set read_fds; FD_ZERO(&read_fds); if (bst->tr.socket > maxfd) maxfd = bst->tr.socket; if (bst->eth.socket > maxfd) maxfd = bst->eth.socket; while (1) { FD_SET(bst->tr.socket, &read_fds); FD_SET(bst->eth.socket, &read_fds); rc = select(maxfd+1, &read_fds, NULL, NULL, NULL); if (rc < 0 && errno != EAGAIN) break; if (FD_ISSET(bst->tr.socket, &read_fds)) tr2eth(bst); if (FD_ISSET(bst->eth.socket, &read_fds)) eth2tr(bst); } return rc; } int main(int argc, char **argv) { struct bridge_state bst; const char *tr_name, *eth_name; if (argc < 3) { fprintf(stderr, "You must specify both TR and ETH device\n"); exit(2); } tr_name = argv[1]; eth_name = argv[2]; bst.tr.socket = open_packet_socket_for_netdev(tr_name, htons(ETH_P_ALL)); if (bst.tr.socket < 0) { fprintf(stderr, "Error opening TR\n"); exit(1); } bst.eth.socket = open_packet_socket_for_netdev(eth_name, htons(ETH_P_802_2)); if (bst.eth.socket < 0) { fprintf(stderr, "Error opening ETH\n"); exit(1); } bridge_main(&bst); exit(0); }