blob: 82df63db30da8335c8d6509a97066b710a0f2100 [file] [log] [blame]
/*
* 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 <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 <net/if.h>
#include <sys/capability.h>
#include <sys/uio.h>
#include <private/android_filesystem_config.h>
#include "clatd.h"
#include "config.h"
#include "dump.h"
#include "getaddr.h"
#include "logging.h"
#include "resolv_netid.h"
#include "ring.h"
#include "setif.h"
#include "translate.h"
#include "tun.h"
/* 40 bytes IPv6 header - 20 bytes IPv4 header + 8 bytes fragment header */
#define MTU_DELTA 28
volatile sig_atomic_t running = 1;
/* function: stop_loop
* signal handler: stop the event loop
*/
void stop_loop() { running = 0; }
/* function: configure_packet_socket
* Binds the packet socket and attaches the receive filter to it.
* sock - the socket to configure
*/
int configure_packet_socket(int sock) {
uint32_t *ipv6 = Global_Clatd_Config.ipv6_local_subnet.s6_addr32;
// clang-format off
struct sock_filter filter_code[] = {
// Load the first four bytes of the IPv6 destination address (starts 24 bytes in).
// Compare it against the first four bytes of our IPv6 address, in host byte order (BPF loads
// are always in host byte order). If it matches, continue with next instruction (JMP 0). If it
// doesn't match, jump ahead to statement that returns 0 (ignore packet). Repeat for the other
// three words of the IPv6 address, and if they all match, return PACKETLEN (accept packet).
BPF_STMT(BPF_LD | BPF_W | BPF_ABS, 24),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(ipv6[0]), 0, 7),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS, 28),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(ipv6[1]), 0, 5),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS, 32),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(ipv6[2]), 0, 3),
BPF_STMT(BPF_LD | BPF_W | BPF_ABS, 36),
BPF_JUMP(BPF_JMP | BPF_JEQ | BPF_K, htonl(ipv6[3]), 0, 1),
BPF_STMT(BPF_RET | BPF_K, PACKETLEN),
BPF_STMT(BPF_RET | BPF_K, 0),
};
// clang-format on
struct sock_fprog filter = { sizeof(filter_code) / sizeof(filter_code[0]), filter_code };
if (setsockopt(sock, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter))) {
logmsg(ANDROID_LOG_FATAL, "attach packet filter failed: %s", strerror(errno));
return 0;
}
struct sockaddr_ll sll = {
.sll_family = AF_PACKET,
.sll_protocol = htons(ETH_P_IPV6),
.sll_ifindex = if_nametoindex(Global_Clatd_Config.default_pdp_interface),
.sll_pkttype = PACKET_OTHERHOST, // The 464xlat IPv6 address is not assigned to the kernel.
};
if (bind(sock, (struct sockaddr *)&sll, sizeof(sll))) {
logmsg(ANDROID_LOG_FATAL, "binding packet socket: %s", strerror(errno));
return 0;
}
return 1;
}
/* function: ipv4_address_generate
* picks a free IPv4 address from the local subnet or exits if there are no free addresses
* returns: the IPv4 address as an in_addr_t
*/
static in_addr_t ipv4_address_generate() {
// Pick an IPv4 address to use by finding a free address in the configured prefix. Technically,
// there is a race here - if another clatd calls config_select_ipv4_address after we do, but
// before we call add_address, it can end up having the same IP address as we do. But the time
// window in which this can happen is extremely small, and even if we end up with a duplicate
// address, the only damage is that IPv4 TCP connections won't be reset until both interfaces go
// down.
in_addr_t localaddr = config_select_ipv4_address(&Global_Clatd_Config.ipv4_local_subnet,
Global_Clatd_Config.ipv4_local_prefixlen);
if (localaddr == INADDR_NONE) {
logmsg(ANDROID_LOG_FATAL, "No free IPv4 address in %s/%d",
inet_ntoa(Global_Clatd_Config.ipv4_local_subnet),
Global_Clatd_Config.ipv4_local_prefixlen);
exit(1);
}
return localaddr;
}
/* function: ipv4_address_from_cmdline
* configures the IPv4 address specified on the command line, or exits if the address is not valid
* v4_addr - a string, the IPv4 address
* returns: the IPv4 address as an in_addr_t
*/
static in_addr_t ipv4_address_from_cmdline(const char *v4_addr) {
in_addr_t localaddr;
if (!inet_pton(AF_INET, v4_addr, &localaddr)) {
logmsg(ANDROID_LOG_FATAL, "Invalid IPv4 address %s", v4_addr);
exit(1);
}
return localaddr;
}
/* function: configure_tun_ip
* configures the ipv4 and ipv6 addresses on the tunnel interface
* tunnel - tun device data
* mtu - mtu of tun device
*/
void configure_tun_ip(const struct tun_data *tunnel, const char *v4_addr, int mtu) {
if (v4_addr) {
Global_Clatd_Config.ipv4_local_subnet.s_addr = ipv4_address_from_cmdline(v4_addr);
} else {
Global_Clatd_Config.ipv4_local_subnet.s_addr = ipv4_address_generate();
}
char addrstr[INET_ADDRSTRLEN];
inet_ntop(AF_INET, &Global_Clatd_Config.ipv4_local_subnet, addrstr, sizeof(addrstr));
logmsg(ANDROID_LOG_INFO, "Using IPv4 address %s on %s", addrstr, tunnel->device4);
// Configure the interface before bringing it up. As soon as we bring the interface up, the
// framework will be notified and will assume the interface's configuration has been finalized.
int status = add_address(tunnel->device4, AF_INET, &Global_Clatd_Config.ipv4_local_subnet, 32,
&Global_Clatd_Config.ipv4_local_subnet);
if (status < 0) {
logmsg(ANDROID_LOG_FATAL, "configure_tun_ip/if_address(4) failed: %s", strerror(-status));
exit(1);
}
status = if_up(tunnel->device4, mtu);
if (status < 0) {
logmsg(ANDROID_LOG_FATAL, "configure_tun_ip/if_up(4) failed: %s", strerror(-status));
exit(1);
}
}
/* function: set_capability
* set the permitted, effective and inheritable capabilities of the current
* thread
*/
void set_capability(uint64_t target_cap) {
struct __user_cap_header_struct header = {
.version = _LINUX_CAPABILITY_VERSION_3,
.pid = 0 // 0 = change myself
};
struct __user_cap_data_struct cap[_LINUX_CAPABILITY_U32S_3] = {};
cap[0].permitted = cap[0].effective = cap[0].inheritable = target_cap;
cap[1].permitted = cap[1].effective = cap[1].inheritable = target_cap >> 32;
if (capset(&header, cap) < 0) {
logmsg(ANDROID_LOG_FATAL, "capset failed: %s", strerror(errno));
exit(1);
}
}
/* function: drop_root_but_keep_caps
* drops root privs but keeps the needed capabilities
*/
void drop_root_but_keep_caps() {
gid_t groups[] = { AID_INET, AID_VPN };
if (setgroups(sizeof(groups) / sizeof(groups[0]), groups) < 0) {
logmsg(ANDROID_LOG_FATAL, "setgroups failed: %s", strerror(errno));
exit(1);
}
prctl(PR_SET_KEEPCAPS, 1);
if (setresgid(AID_CLAT, AID_CLAT, AID_CLAT) < 0) {
logmsg(ANDROID_LOG_FATAL, "setresgid failed: %s", strerror(errno));
exit(1);
}
if (setresuid(AID_CLAT, AID_CLAT, AID_CLAT) < 0) {
logmsg(ANDROID_LOG_FATAL, "setresuid failed: %s", strerror(errno));
exit(1);
}
// keep CAP_NET_RAW capability to open raw socket, and CAP_IPC_LOCK for mmap
// to lock memory.
set_capability((1 << CAP_NET_ADMIN) |
(1 << CAP_NET_RAW) |
(1 << CAP_IPC_LOCK));
}
/* function: open_sockets
* opens a packet socket to receive IPv6 packets and a raw socket to send them
* tunnel - tun device data
* mark - the socket mark to use for the sending raw socket
*/
void open_sockets(struct tun_data *tunnel, uint32_t mark) {
int rawsock = socket(AF_INET6, SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC, IPPROTO_RAW);
if (rawsock < 0) {
logmsg(ANDROID_LOG_FATAL, "raw socket failed: %s", strerror(errno));
exit(1);
}
int off = 0;
if (setsockopt(rawsock, SOL_IPV6, IPV6_CHECKSUM, &off, sizeof(off)) < 0) {
logmsg(ANDROID_LOG_WARN, "could not disable checksum on raw socket: %s", strerror(errno));
}
if (mark != MARK_UNSET && setsockopt(rawsock, SOL_SOCKET, SO_MARK, &mark, sizeof(mark)) < 0) {
logmsg(ANDROID_LOG_ERROR, "could not set mark on raw socket: %s", strerror(errno));
}
tunnel->write_fd6 = rawsock;
tunnel->read_fd6 = ring_create(tunnel);
if (tunnel->read_fd6 < 0) {
exit(1);
}
}
int ipv6_address_changed(const char *interface) {
union anyip *interface_ip;
interface_ip = getinterface_ip(interface, AF_INET6);
if (!interface_ip) {
logmsg(ANDROID_LOG_ERROR, "Unable to find an IPv6 address on interface %s", interface);
return 1;
}
if (!ipv6_prefix_equal(&interface_ip->ip6, &Global_Clatd_Config.ipv6_local_subnet)) {
char oldstr[INET6_ADDRSTRLEN];
char newstr[INET6_ADDRSTRLEN];
inet_ntop(AF_INET6, &Global_Clatd_Config.ipv6_local_subnet, oldstr, sizeof(oldstr));
inet_ntop(AF_INET6, &interface_ip->ip6, newstr, sizeof(newstr));
logmsg(ANDROID_LOG_INFO, "IPv6 prefix on %s changed: %s -> %s", interface, oldstr, newstr);
free(interface_ip);
return 1;
} else {
free(interface_ip);
return 0;
}
}
/* function: clat_ipv6_address_from_interface
* picks the clat IPv6 address based on the interface address
* interface - uplink interface name
* returns: 1 on success, 0 on failure
*/
static int clat_ipv6_address_from_interface(const char *interface) {
union anyip *interface_ip;
// TODO: check that the prefix length is /64.
interface_ip = getinterface_ip(interface, AF_INET6);
if (!interface_ip) {
logmsg(ANDROID_LOG_ERROR, "Unable to find an IPv6 address on interface %s", interface);
return 0;
}
// Generate an interface ID.
config_generate_local_ipv6_subnet(&interface_ip->ip6);
Global_Clatd_Config.ipv6_local_subnet = interface_ip->ip6;
free(interface_ip);
return 1;
}
/* function: clat_ipv6_address_from_cmdline
* parses the clat IPv6 address from the command line
* v4_addr - a string, the IPv6 address
* returns: 1 on success, 0 on failure
*/
static int clat_ipv6_address_from_cmdline(const char *v6_addr) {
if (!inet_pton(AF_INET6, v6_addr, &Global_Clatd_Config.ipv6_local_subnet)) {
logmsg(ANDROID_LOG_FATAL, "Invalid source address %s", v6_addr);
return 0;
}
return 1;
}
/* function: configure_clat_ipv6_address
* picks the clat IPv6 address and configures packet translation to use it.
* tunnel - tun device data
* interface - uplink interface name
* returns: 1 on success, 0 on failure
*/
int configure_clat_ipv6_address(const struct tun_data *tunnel, const char *interface,
const char *v6_addr) {
int ret;
if (v6_addr) {
ret = clat_ipv6_address_from_cmdline(v6_addr);
} else {
ret = clat_ipv6_address_from_interface(interface);
}
if (!ret) return 0;
char addrstr[INET6_ADDRSTRLEN];
inet_ntop(AF_INET6, &Global_Clatd_Config.ipv6_local_subnet, addrstr, sizeof(addrstr));
logmsg(ANDROID_LOG_INFO, "Using IPv6 address %s on %s", addrstr, interface);
// Start translating packets to the new prefix.
add_anycast_address(tunnel->write_fd6, &Global_Clatd_Config.ipv6_local_subnet, interface);
// Update our packet socket filter to reflect the new 464xlat IP address.
if (!configure_packet_socket(tunnel->read_fd6)) {
// Things aren't going to work. Bail out and hope we have better luck next time.
// We don't log an error here because configure_packet_socket has already done so.
return 0;
}
return 1;
}
int detect_mtu(const struct in6_addr *plat_subnet, uint32_t plat_suffix, uint32_t mark) {
// Create an IPv6 UDP socket.
int s = socket(AF_INET6, SOCK_DGRAM | SOCK_CLOEXEC, 0);
if (s < 0) {
logmsg(ANDROID_LOG_FATAL, "socket(AF_INET6, SOCK_DGRAM, 0) failed");
exit(1);
}
// Socket's mark affects routing decisions (network selection)
if ((mark != MARK_UNSET) && setsockopt(s, SOL_SOCKET, SO_MARK, &mark, sizeof(mark))) {
logmsg(ANDROID_LOG_FATAL, "setsockopt(SOL_SOCKET, SO_MARK) failed: %s", strerror(errno));
exit(1);
}
// Try to connect udp socket to plat_subnet(96 bits):plat_suffix(32 bits)
struct sockaddr_in6 dst = {
.sin6_family = AF_INET6,
.sin6_addr = *plat_subnet,
};
dst.sin6_addr.s6_addr32[3] = plat_suffix;
if (connect(s, (struct sockaddr *)&dst, sizeof(dst))) {
logmsg(ANDROID_LOG_FATAL, "connect() failed: %s", strerror(errno));
exit(1);
}
// Fetch the socket's IPv6 mtu - this is effectively fetching mtu from routing table
int mtu;
socklen_t sz_mtu = sizeof(mtu);
if (getsockopt(s, SOL_IPV6, IPV6_MTU, &mtu, &sz_mtu)) {
logmsg(ANDROID_LOG_FATAL, "getsockopt(SOL_IPV6, IPV6_MTU) failed: %s", strerror(errno));
exit(1);
}
if (sz_mtu != sizeof(mtu)) {
logmsg(ANDROID_LOG_FATAL, "getsockopt(SOL_IPV6, IPV6_MTU) returned unexpected size: %d",
sz_mtu);
exit(1);
}
close(s);
return mtu;
}
/* function: configure_interface
* reads the configuration and applies it to the interface
* uplink_interface - network interface to use to reach the ipv6 internet
* plat_prefix - PLAT prefix to use
* tunnel - tun device data
* net_id - NetID to use, NETID_UNSET indicates use of default network
* mark - the socket mark to use for the sending raw socket
*/
void configure_interface(const char *uplink_interface, const char *plat_prefix, const char *v4_addr,
const char *v6_addr, struct tun_data *tunnel, unsigned net_id,
uint32_t mark) {
if (!read_config("/system/etc/clatd.conf", uplink_interface, plat_prefix, net_id)) {
logmsg(ANDROID_LOG_FATAL, "read_config failed");
exit(1);
}
int mtu = detect_mtu(&Global_Clatd_Config.plat_subnet, htonl(0x08080808), mark);
// clamp to minimum ipv6 mtu - this probably cannot ever trigger
if (mtu < 1280) mtu = 1280;
// clamp to buffer size
if (mtu > MAXMTU) mtu = MAXMTU;
// decrease by ipv6(40) + ipv6 fragmentation header(8) vs ipv4(20) overhead of 28 bytes
mtu -= MTU_DELTA;
logmsg(ANDROID_LOG_WARN, "ipv4 mtu is %d", mtu);
configure_tun_ip(tunnel, v4_addr, mtu);
if (!configure_clat_ipv6_address(tunnel, uplink_interface, v6_addr)) {
exit(1);
}
}
/* function: read_packet
* reads a packet from the tunnel fd and translates it
* read_fd - file descriptor to read original packet from
* write_fd - file descriptor to write translated packet to
* to_ipv6 - whether the packet is to be translated to ipv6 or ipv4
*/
void read_packet(int read_fd, int write_fd, int to_ipv6) {
ssize_t readlen;
uint8_t buf[PACKETLEN], *packet;
readlen = read(read_fd, buf, PACKETLEN);
if (readlen < 0) {
if (errno != EAGAIN) {
logmsg(ANDROID_LOG_WARN, "read_packet/read error: %s", strerror(errno));
}
return;
} else if (readlen == 0) {
logmsg(ANDROID_LOG_WARN, "read_packet/tun interface removed");
running = 0;
return;
}
struct tun_pi *tun_header = (struct tun_pi *)buf;
if (readlen < (ssize_t)sizeof(*tun_header)) {
logmsg(ANDROID_LOG_WARN, "read_packet/short read: got %ld bytes", readlen);
return;
}
uint16_t proto = ntohs(tun_header->proto);
if (proto != ETH_P_IP) {
logmsg(ANDROID_LOG_WARN, "%s: unknown packet type = 0x%x", __func__, proto);
return;
}
if (tun_header->flags != 0) {
logmsg(ANDROID_LOG_WARN, "%s: unexpected flags = %d", __func__, tun_header->flags);
}
packet = (uint8_t *)(tun_header + 1);
readlen -= sizeof(*tun_header);
translate_packet(write_fd, to_ipv6, packet, readlen);
}
/* 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) {
time_t last_interface_poll;
struct pollfd wait_fd[] = {
{ tunnel->read_fd6, POLLIN, 0 },
{ tunnel->fd4, POLLIN, 0 },
};
// start the poll timer
last_interface_poll = time(NULL);
while (running) {
if (poll(wait_fd, ARRAY_SIZE(wait_fd), NO_TRAFFIC_INTERFACE_POLL_FREQUENCY * 1000) == -1) {
if (errno != EINTR) {
logmsg(ANDROID_LOG_WARN, "event_loop/poll returned an error: %s", strerror(errno));
}
} else {
if (wait_fd[0].revents & POLLIN) {
ring_read(&tunnel->ring, tunnel->fd4, 0 /* to_ipv6 */);
}
// If any other bit is set, assume it's due to an error (i.e. POLLERR).
if (wait_fd[0].revents & ~POLLIN) {
// ring_read doesn't clear the error indication on the socket.
recv(tunnel->read_fd6, NULL, 0, MSG_PEEK);
logmsg(ANDROID_LOG_WARN, "event_loop: clearing error on read_fd6: %s", strerror(errno));
}
// Call read_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[1].revents) {
read_packet(tunnel->fd4, tunnel->write_fd6, 1 /* to_ipv6 */);
}
}
time_t now = time(NULL);
if (last_interface_poll < (now - INTERFACE_POLL_FREQUENCY)) {
if (ipv6_address_changed(Global_Clatd_Config.default_pdp_interface)) {
break;
}
}
}
}