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Diffstat (limited to 'clatd.c')
| -rw-r--r-- | clatd.c | 307 |
1 files changed, 0 insertions, 307 deletions
diff --git a/clatd.c b/clatd.c deleted file mode 100644 index bac8b1d..0000000 --- a/clatd.c +++ /dev/null @@ -1,307 +0,0 @@ -/* - * Copyright 2012 Daniel Drown - * - * Licensed under the Apache License, Version 2.0 (the "License"); - * you may not use this file except in compliance with the License. - * You may obtain a copy of the License at - * - * http://www.apache.org/licenses/LICENSE-2.0 - * - * Unless required by applicable law or agreed to in writing, software - * distributed under the License is distributed on an "AS IS" BASIS, - * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - * See the License for the specific language governing permissions and - * limitations under the License. - * - * clatd.c - tun interface setup and main event loop - */ -#include <arpa/inet.h> -#include <errno.h> -#include <fcntl.h> -#include <poll.h> -#include <signal.h> -#include <stdbool.h> -#include <stdio.h> -#include <stdlib.h> -#include <string.h> -#include <sys/ioctl.h> -#include <sys/prctl.h> -#include <sys/stat.h> -#include <sys/types.h> -#include <time.h> -#include <unistd.h> - -#include <linux/filter.h> -#include <linux/if.h> -#include <linux/if_ether.h> -#include <linux/if_packet.h> -#include <linux/if_tun.h> -#include <linux/virtio_net.h> -#include <net/if.h> -#include <sys/uio.h> - -#include "clatd.h" -#include "checksum.h" -#include "config.h" -#include "dump.h" -#include "logging.h" -#include "translate.h" - -struct clat_config Global_Clatd_Config; - -volatile sig_atomic_t running = 1; - -// reads IPv6 packet from AF_PACKET socket, translates to IPv4, writes to tun -void process_packet_6_to_4(struct tun_data *tunnel) { - // ethernet header is 14 bytes, plus 4 for a normal VLAN tag or 8 for Q-in-Q - // we don't really support vlans (or especially Q-in-Q)... - // but a few bytes of extra buffer space doesn't hurt... - struct { - struct virtio_net_hdr vnet; - uint8_t payload[22 + MAXMTU]; - char pad; // +1 to make packet truncation obvious - } buf; - struct iovec iov = { - .iov_base = &buf, - .iov_len = sizeof(buf), - }; - char cmsg_buf[CMSG_SPACE(sizeof(struct tpacket_auxdata))]; - struct msghdr msgh = { - .msg_iov = &iov, - .msg_iovlen = 1, - .msg_control = cmsg_buf, - .msg_controllen = sizeof(cmsg_buf), - }; - ssize_t readlen = recvmsg(tunnel->read_fd6, &msgh, /*flags*/ 0); - - if (readlen < 0) { - if (errno != EAGAIN) { - logmsg(ANDROID_LOG_WARN, "%s: read error: %s", __func__, strerror(errno)); - } - return; - } else if (readlen == 0) { - logmsg(ANDROID_LOG_WARN, "%s: packet socket removed?", __func__); - running = 0; - return; - } else if (readlen >= sizeof(buf)) { - logmsg(ANDROID_LOG_WARN, "%s: read truncation - ignoring pkt", __func__); - return; - } - - bool ok = false; - __u32 tp_status = 0; - __u16 tp_net = 0; - - for (struct cmsghdr *cmsg = CMSG_FIRSTHDR(&msgh); cmsg != NULL; cmsg = CMSG_NXTHDR(&msgh,cmsg)) { - if (cmsg->cmsg_level == SOL_PACKET && cmsg->cmsg_type == PACKET_AUXDATA) { - struct tpacket_auxdata *aux = (struct tpacket_auxdata *)CMSG_DATA(cmsg); - ok = true; - tp_status = aux->tp_status; - tp_net = aux->tp_net; - break; - } - } - - if (!ok) { - // theoretically this should not happen... - static bool logged = false; - if (!logged) { - logmsg(ANDROID_LOG_ERROR, "%s: failed to fetch tpacket_auxdata cmsg", __func__); - logged = true; - } - } - - const int payload_offset = offsetof(typeof(buf), payload); - if (readlen < payload_offset + tp_net) { - logmsg(ANDROID_LOG_WARN, "%s: ignoring %zd byte pkt shorter than %d+%u L2 header", - __func__, readlen, payload_offset, tp_net); - return; - } - - const int pkt_len = readlen - payload_offset; - - // This will detect a skb->ip_summed == CHECKSUM_PARTIAL packet with non-final L4 checksum - if (tp_status & TP_STATUS_CSUMNOTREADY) { - static bool logged = false; - if (!logged) { - logmsg(ANDROID_LOG_WARN, "%s: L4 checksum calculation required", __func__); - logged = true; - } - - // These are non-negative by virtue of csum_start/offset being u16 - const int cs_start = buf.vnet.csum_start; - const int cs_offset = cs_start + buf.vnet.csum_offset; - if (cs_start > pkt_len) { - logmsg(ANDROID_LOG_ERROR, "%s: out of range - checksum start %d > %d", - __func__, cs_start, pkt_len); - } else if (cs_offset + 1 >= pkt_len) { - logmsg(ANDROID_LOG_ERROR, "%s: out of range - checksum offset %d + 1 >= %d", - __func__, cs_offset, pkt_len); - } else { - uint16_t csum = ip_checksum(buf.payload + cs_start, pkt_len - cs_start); - if (!csum) csum = 0xFFFF; // required fixup for UDP, TCP must live with it - buf.payload[cs_offset] = csum & 0xFF; - buf.payload[cs_offset + 1] = csum >> 8; - } - } - - translate_packet(tunnel->fd4, 0 /* to_ipv6 */, buf.payload + tp_net, pkt_len - tp_net); -} - -// reads TUN_PI + L3 IPv4 packet from tun, translates to IPv6, writes to AF_INET6/RAW socket -void process_packet_4_to_6(struct tun_data *tunnel) { - struct { - struct tun_pi pi; - uint8_t payload[MAXMTU]; - char pad; // +1 byte to make packet truncation obvious - } buf; - ssize_t readlen = read(tunnel->fd4, &buf, sizeof(buf)); - - if (readlen < 0) { - if (errno != EAGAIN) { - logmsg(ANDROID_LOG_WARN, "%s: read error: %s", __func__, strerror(errno)); - } - return; - } else if (readlen == 0) { - logmsg(ANDROID_LOG_WARN, "%s: tun interface removed", __func__); - running = 0; - return; - } else if (readlen >= sizeof(buf)) { - logmsg(ANDROID_LOG_WARN, "%s: read truncation - ignoring pkt", __func__); - return; - } - - const int payload_offset = offsetof(typeof(buf), payload); - - if (readlen < payload_offset) { - logmsg(ANDROID_LOG_WARN, "%s: short read: got %ld bytes", __func__, readlen); - return; - } - - const int pkt_len = readlen - payload_offset; - - uint16_t proto = ntohs(buf.pi.proto); - if (proto != ETH_P_IP) { - logmsg(ANDROID_LOG_WARN, "%s: unknown packet type = 0x%x", __func__, proto); - return; - } - - if (buf.pi.flags != 0) { - logmsg(ANDROID_LOG_WARN, "%s: unexpected flags = %d", __func__, buf.pi.flags); - } - - translate_packet(tunnel->write_fd6, 1 /* to_ipv6 */, buf.payload, pkt_len); -} - -// IPv6 DAD packet format: -// Ethernet header (if needed) will be added by the kernel: -// u8[6] src_mac; u8[6] dst_mac '33:33:ff:XX:XX:XX'; be16 ethertype '0x86DD' -// IPv6 header: -// be32 0x60000000 - ipv6, tclass 0, flowlabel 0 -// be16 payload_length '32'; u8 nxt_hdr ICMPv6 '58'; u8 hop limit '255' -// u128 src_ip6 '::' -// u128 dst_ip6 'ff02::1:ffXX:XXXX' -// ICMPv6 header: -// u8 type '135'; u8 code '0'; u16 icmp6 checksum; u32 reserved '0' -// ICMPv6 neighbour solicitation payload: -// u128 tgt_ip6 -// ICMPv6 ND options: -// u8 opt nr '14'; u8 length '1'; u8[6] nonce '6 random bytes' -void send_dad(int fd, const struct in6_addr* tgt) { - struct { - struct ip6_hdr ip6h; - struct nd_neighbor_solicit ns; - uint8_t ns_opt_nr; - uint8_t ns_opt_len; - uint8_t ns_opt_nonce[6]; - } dad_pkt = { - .ip6h = { - .ip6_flow = htonl(6 << 28), // v6, 0 tclass, 0 flowlabel - .ip6_plen = htons(sizeof(dad_pkt) - sizeof(struct ip6_hdr)), // payload length, ie. 32 - .ip6_nxt = IPPROTO_ICMPV6, // 58 - .ip6_hlim = 255, - .ip6_src = {}, // :: - .ip6_dst.s6_addr = { - 0xFF, 0x02, 0, 0, - 0, 0, 0, 0, - 0, 0, 0, 1, - 0xFF, tgt->s6_addr[13], tgt->s6_addr[14], tgt->s6_addr[15], - }, // ff02::1:ffXX:XXXX - multicast group address derived from bottom 24-bits of tgt - }, - .ns = { - .nd_ns_type = ND_NEIGHBOR_SOLICIT, // 135 - .nd_ns_code = 0, - .nd_ns_cksum = 0, // will be calculated later - .nd_ns_reserved = 0, - .nd_ns_target = *tgt, - }, - .ns_opt_nr = 14, // icmp6 option 'nonce' from RFC3971 - .ns_opt_len = 1, // in units of 8 bytes, including option nr and len - .ns_opt_nonce = {}, // opt_len *8 - sizeof u8(opt_nr) - sizeof u8(opt_len) = 6 ranodmized bytes - }; - arc4random_buf(&dad_pkt.ns_opt_nonce, sizeof(dad_pkt.ns_opt_nonce)); - - // 40 byte IPv6 header + 8 byte ICMPv6 header + 16 byte ipv6 target address + 8 byte nonce option - _Static_assert(sizeof(dad_pkt) == 40 + 8 + 16 + 8, "sizeof dad packet != 72"); - - // IPv6 header checksum is standard negated 16-bit one's complement sum over the icmpv6 pseudo - // header (which includes payload length, nextheader, and src/dst ip) and the icmpv6 payload. - // - // Src/dst ip immediately prefix the icmpv6 header itself, so can be handled along - // with the payload. We thus only need to manually account for payload len & next header. - // - // The magic '8' is simply the offset of the ip6_src field in the ipv6 header, - // ie. we're skipping over the ipv6 version, tclass, flowlabel, payload length, next header - // and hop limit fields, because they're not quite where we want them to be. - // - // ip6_plen is already in network order, while ip6_nxt is a single byte and thus needs htons(). - uint32_t csum = dad_pkt.ip6h.ip6_plen + htons(dad_pkt.ip6h.ip6_nxt); - csum = ip_checksum_add(csum, &dad_pkt.ip6h.ip6_src, sizeof(dad_pkt) - 8); - dad_pkt.ns.nd_ns_cksum = ip_checksum_finish(csum); - - const struct sockaddr_in6 dst = { - .sin6_family = AF_INET6, - .sin6_addr = dad_pkt.ip6h.ip6_dst, - .sin6_scope_id = if_nametoindex(Global_Clatd_Config.native_ipv6_interface), - }; - - sendto(fd, &dad_pkt, sizeof(dad_pkt), 0 /*flags*/, (const struct sockaddr *)&dst, sizeof(dst)); -} - -/* function: event_loop - * reads packets from the tun network interface and passes them down the stack - * tunnel - tun device data - */ -void event_loop(struct tun_data *tunnel) { - // Apparently some network gear will refuse to perform NS for IPs that aren't DAD'ed, - // this would then result in an ipv6-only network with working native ipv6, working - // IPv4 via DNS64, but non-functioning IPv4 via CLAT (ie. IPv4 literals + IPv4 only apps). - // The kernel itself doesn't do DAD for anycast ips (but does handle IPV6 MLD and handle ND). - // So we'll spoof dad here, and yeah, we really should check for a response and in - // case of failure pick a different IP. Seeing as 48-bits of the IP are utterly random - // (with the other 16 chosen to guarantee checksum neutrality) this seems like a remote - // concern... - // TODO: actually perform true DAD - send_dad(tunnel->write_fd6, &Global_Clatd_Config.ipv6_local_subnet); - - struct pollfd wait_fd[] = { - { tunnel->read_fd6, POLLIN, 0 }, - { tunnel->fd4, POLLIN, 0 }, - }; - - while (running) { - if (poll(wait_fd, ARRAY_SIZE(wait_fd), -1) == -1) { - if (errno != EINTR) { - logmsg(ANDROID_LOG_WARN, "event_loop/poll returned an error: %s", strerror(errno)); - } - } else { - // Call process_packet if the socket has data to be read, but also if an - // error is waiting. If we don't call read() after getting POLLERR, a - // subsequent poll() will return immediately with POLLERR again, - // causing this code to spin in a loop. Calling read() will clear the - // socket error flag instead. - if (wait_fd[0].revents) process_packet_6_to_4(tunnel); - if (wait_fd[1].revents) process_packet_4_to_6(tunnel); - } - } -} |