/* This file is part of GNUnet. (C) 2010, 2011, 2012 Christian Grothoff GNUnet is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version. GNUnet is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNUnet; see the file COPYING. If not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. */ /** * @file exit/gnunet-helper-exit.c * * @brief the helper for exit nodes. Opens a virtual * network-interface, sends data received on the if to stdout, sends * data received on stdin to the interface. The code also enables * IPv4/IPv6 forwarding and NAT on the current system (the latter on * an interface specified on the command-line); these changes to the * network configuration are NOT automatically undone when the program * is stopped (this is because we cannot be sure that some other * application didn't enable them before or after us; also, these * changes should be mostly harmless as it simply turns the system * into a router). * * @author Philipp Tölke * @author Christian Grothoff * * The following list of people have reviewed this code and considered * it safe since the last modification (if you reviewed it, please * have your name added to the list): * * - Philipp Tölke */ #include "platform.h" #include /** * Need 'struct GNUNET_MessageHeader'. */ #include "gnunet_common.h" /** * Need VPN message types. */ #include "gnunet_protocols.h" /** * Should we print (interesting|debug) messages that can happen during * normal operation? */ #define DEBUG GNUNET_NO /** * Maximum size of a GNUnet message (GNUNET_SERVER_MAX_MESSAGE_SIZE) */ #define MAX_SIZE 65536 /** * Path to 'sysctl' binary. */ static const char *sbin_sysctl; /** * Path to 'iptables' binary. */ static const char *sbin_iptables; #ifndef _LINUX_IN6_H /** * This is in linux/include/net/ipv6.h, but not always exported... */ struct in6_ifreq { struct in6_addr ifr6_addr; __u32 ifr6_prefixlen; int ifr6_ifindex; }; #endif /** * Run the given command and wait for it to complete. * * @param file name of the binary to run * @param cmd command line arguments (as given to 'execv') * @return 0 on success, 1 on any error */ static int fork_and_exec (const char *file, char *const cmd[]) { int status; pid_t pid; pid_t ret; pid = fork (); if (-1 == pid) { fprintf (stderr, "fork failed: %s\n", strerror (errno)); return 1; } if (0 == pid) { /* we are the child process */ /* close stdin/stdout to not cause interference with the helper's main protocol! */ (void) close (0); (void) close (1); (void) execv (file, cmd); /* can only get here on error */ fprintf (stderr, "exec `%s' failed: %s\n", file, strerror (errno)); _exit (1); } /* keep running waitpid as long as the only error we get is 'EINTR' */ while ( (-1 == (ret = waitpid (pid, &status, 0))) && (errno == EINTR) ); if (-1 == ret) { fprintf (stderr, "waitpid failed: %s\n", strerror (errno)); return 1; } if (! (WIFEXITED (status) && (0 == WEXITSTATUS (status)))) return 1; /* child process completed and returned success, we're happy */ return 0; } /** * Creates a tun-interface called dev; * * @param dev is asumed to point to a char[IFNAMSIZ] * if *dev == '\\0', uses the name supplied by the kernel; * @return the fd to the tun or -1 on error */ static int init_tun (char *dev) { struct ifreq ifr; int fd; if (NULL == dev) { errno = EINVAL; return -1; } if (-1 == (fd = open ("/dev/net/tun", O_RDWR))) { fprintf (stderr, "Error opening `%s': %s\n", "/dev/net/tun", strerror (errno)); return -1; } if (fd >= FD_SETSIZE) { fprintf (stderr, "File descriptor to large: %d", fd); (void) close (fd); return -1; } memset (&ifr, 0, sizeof (ifr)); ifr.ifr_flags = IFF_TUN; if ('\0' != *dev) strncpy (ifr.ifr_name, dev, IFNAMSIZ); if (-1 == ioctl (fd, TUNSETIFF, (void *) &ifr)) { fprintf (stderr, "Error with ioctl on `%s': %s\n", "/dev/net/tun", strerror (errno)); (void) close (fd); return -1; } strcpy (dev, ifr.ifr_name); return fd; } /** * @brief Sets the IPv6-Address given in address on the interface dev * * @param dev the interface to configure * @param address the IPv6-Address * @param prefix_len the length of the network-prefix */ static void set_address6 (const char *dev, const char *address, unsigned long prefix_len) { struct ifreq ifr; struct sockaddr_in6 sa6; int fd; struct in6_ifreq ifr6; /* * parse the new address */ memset (&sa6, 0, sizeof (struct sockaddr_in6)); sa6.sin6_family = AF_INET6; if (1 != inet_pton (AF_INET6, address, &sa6.sin6_addr)) { fprintf (stderr, "Failed to parse address `%s': %s\n", address, strerror (errno)); exit (1); } if (-1 == (fd = socket (PF_INET6, SOCK_DGRAM, 0))) { fprintf (stderr, "Error creating socket: %s\n", strerror (errno)); exit (1); } memset (&ifr, 0, sizeof (struct ifreq)); /* * Get the index of the if */ strncpy (ifr.ifr_name, dev, IFNAMSIZ); if (-1 == ioctl (fd, SIOGIFINDEX, &ifr)) { fprintf (stderr, "ioctl failed at %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } memset (&ifr6, 0, sizeof (struct in6_ifreq)); ifr6.ifr6_addr = sa6.sin6_addr; ifr6.ifr6_ifindex = ifr.ifr_ifindex; ifr6.ifr6_prefixlen = prefix_len; /* * Set the address */ if (-1 == ioctl (fd, SIOCSIFADDR, &ifr6)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } /* * Get the flags */ if (-1 == ioctl (fd, SIOCGIFFLAGS, &ifr)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } /* * Add the UP and RUNNING flags */ ifr.ifr_flags |= IFF_UP | IFF_RUNNING; if (-1 == ioctl (fd, SIOCSIFFLAGS, &ifr)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } if (0 != close (fd)) { fprintf (stderr, "close failed: %s\n", strerror (errno)); exit (1); } } /** * @brief Sets the IPv4-Address given in address on the interface dev * * @param dev the interface to configure * @param address the IPv4-Address * @param mask the netmask */ static void set_address4 (const char *dev, const char *address, const char *mask) { int fd; struct sockaddr_in *addr; struct ifreq ifr; memset (&ifr, 0, sizeof (struct ifreq)); addr = (struct sockaddr_in *) &(ifr.ifr_addr); addr->sin_family = AF_INET; /* * Parse the address */ if (1 != inet_pton (AF_INET, address, &addr->sin_addr.s_addr)) { fprintf (stderr, "Failed to parse address `%s': %s\n", address, strerror (errno)); exit (1); } if (-1 == (fd = socket (PF_INET, SOCK_DGRAM, 0))) { fprintf (stderr, "Error creating socket: %s\n", strerror (errno)); exit (1); } strncpy (ifr.ifr_name, dev, IFNAMSIZ); /* * Set the address */ if (-1 == ioctl (fd, SIOCSIFADDR, &ifr)) { fprintf (stderr, "ioctl failed at %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } /* * Parse the netmask */ addr = (struct sockaddr_in *) &(ifr.ifr_netmask); if (1 != inet_pton (AF_INET, mask, &addr->sin_addr.s_addr)) { fprintf (stderr, "Failed to parse address `%s': %s\n", mask, strerror (errno)); (void) close (fd); exit (1); } /* * Set the netmask */ if (-1 == ioctl (fd, SIOCSIFNETMASK, &ifr)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } /* * Get the flags */ if (-1 == ioctl (fd, SIOCGIFFLAGS, &ifr)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } /* * Add the UP and RUNNING flags */ ifr.ifr_flags |= IFF_UP | IFF_RUNNING; if (-1 == ioctl (fd, SIOCSIFFLAGS, &ifr)) { fprintf (stderr, "ioctl failed at line %d: %s\n", __LINE__, strerror (errno)); (void) close (fd); exit (1); } if (0 != close (fd)) { fprintf (stderr, "close failed: %s\n", strerror (errno)); (void) close (fd); exit (1); } } /** * Start forwarding to and from the tunnel. * * @param fd_tun tunnel FD */ static void run (int fd_tun) { /* * The buffer filled by reading from fd_tun */ unsigned char buftun[MAX_SIZE]; ssize_t buftun_size = 0; unsigned char *buftun_read = NULL; /* * The buffer filled by reading from stdin */ unsigned char bufin[MAX_SIZE]; ssize_t bufin_size = 0; size_t bufin_rpos = 0; unsigned char *bufin_read = NULL; fd_set fds_w; fd_set fds_r; /* read refers to reading from fd_tun, writing to stdout */ int read_open = 1; /* write refers to reading from stdin, writing to fd_tun */ int write_open = 1; while ((1 == read_open) || (1 == write_open)) { FD_ZERO (&fds_w); FD_ZERO (&fds_r); /* * We are supposed to read and the buffer is empty * -> select on read from tun */ if (read_open && (0 == buftun_size)) FD_SET (fd_tun, &fds_r); /* * We are supposed to read and the buffer is not empty * -> select on write to stdout */ if (read_open && (0 != buftun_size)) FD_SET (1, &fds_w); /* * We are supposed to write and the buffer is empty * -> select on read from stdin */ if (write_open && (NULL == bufin_read)) FD_SET (0, &fds_r); /* * We are supposed to write and the buffer is not empty * -> select on write to tun */ if (write_open && (NULL != bufin_read)) FD_SET (fd_tun, &fds_w); int r = select (fd_tun + 1, &fds_r, &fds_w, NULL, NULL); if (-1 == r) { if (EINTR == errno) continue; fprintf (stderr, "select failed: %s\n", strerror (errno)); exit (1); } if (r > 0) { if (FD_ISSET (fd_tun, &fds_r)) { buftun_size = read (fd_tun, buftun + sizeof (struct GNUNET_MessageHeader), MAX_SIZE - sizeof (struct GNUNET_MessageHeader)); if (-1 == buftun_size) { fprintf (stderr, "read-error: %s\n", strerror (errno)); shutdown (fd_tun, SHUT_RD); shutdown (1, SHUT_WR); read_open = 0; buftun_size = 0; } else if (0 == buftun_size) { #if DEBUG fprintf (stderr, "EOF on tun\n"); #endif shutdown (fd_tun, SHUT_RD); shutdown (1, SHUT_WR); read_open = 0; buftun_size = 0; } else { buftun_read = buftun; struct GNUNET_MessageHeader *hdr = (struct GNUNET_MessageHeader *) buftun; buftun_size += sizeof (struct GNUNET_MessageHeader); hdr->type = htons (GNUNET_MESSAGE_TYPE_VPN_HELPER); hdr->size = htons (buftun_size); } } else if (FD_ISSET (1, &fds_w)) { ssize_t written = write (1, buftun_read, buftun_size); if (-1 == written) { #if !DEBUG if (errno != EPIPE) #endif fprintf (stderr, "write-error to stdout: %s\n", strerror (errno)); shutdown (fd_tun, SHUT_RD); shutdown (1, SHUT_WR); read_open = 0; buftun_size = 0; } else if (0 == written) { fprintf (stderr, "write returned 0!?\n"); exit (1); } else { buftun_size -= written; buftun_read += written; } } if (FD_ISSET (0, &fds_r)) { bufin_size = read (0, bufin + bufin_rpos, MAX_SIZE - bufin_rpos); if (-1 == bufin_size) { fprintf (stderr, "read-error: %s\n", strerror (errno)); shutdown (0, SHUT_RD); shutdown (fd_tun, SHUT_WR); write_open = 0; bufin_size = 0; } else if (0 == bufin_size) { #if DEBUG fprintf (stderr, "EOF on stdin\n"); #endif shutdown (0, SHUT_RD); shutdown (fd_tun, SHUT_WR); write_open = 0; bufin_size = 0; } else { struct GNUNET_MessageHeader *hdr; PROCESS_BUFFER: bufin_rpos += bufin_size; if (bufin_rpos < sizeof (struct GNUNET_MessageHeader)) continue; hdr = (struct GNUNET_MessageHeader *) bufin; if (ntohs (hdr->type) != GNUNET_MESSAGE_TYPE_VPN_HELPER) { fprintf (stderr, "protocol violation!\n"); exit (1); } if (ntohs (hdr->size) > bufin_rpos) continue; bufin_read = bufin + sizeof (struct GNUNET_MessageHeader); bufin_size = ntohs (hdr->size) - sizeof (struct GNUNET_MessageHeader); bufin_rpos -= bufin_size + sizeof (struct GNUNET_MessageHeader); } } else if (FD_ISSET (fd_tun, &fds_w)) { ssize_t written = write (fd_tun, bufin_read, bufin_size); if (-1 == written) { fprintf (stderr, "write-error to tun: %s\n", strerror (errno)); shutdown (0, SHUT_RD); shutdown (fd_tun, SHUT_WR); write_open = 0; bufin_size = 0; } else if (0 == written) { fprintf (stderr, "write returned 0!?\n"); exit (1); } else { bufin_size -= written; bufin_read += written; if (0 == bufin_size) { memmove (bufin, bufin_read, bufin_rpos); bufin_read = NULL; /* start reading again */ bufin_size = 0; goto PROCESS_BUFFER; } } } } } } /** * Open VPN tunnel interface. * * @param argc must be 6 * @param argv 0: binary name ("gnunet-helper-exit") * 1: tunnel interface name ("gnunet-exit") * 2: IPv4 "physical" interface name ("eth0"), or "%" to not do IPv4 NAT * 3: IPv6 address ("::1"), or "-" to skip IPv6 * 4: IPv6 netmask length in bits ("64") [ignored if #4 is "-"] * 5: IPv4 address ("1.2.3.4"), or "-" to skip IPv4 * 6: IPv4 netmask ("255.255.0.0") [ignored if #4 is "-"] */ int main (int argc, char **argv) { char dev[IFNAMSIZ]; int fd_tun; int global_ret; if (7 != argc) { fprintf (stderr, "Fatal: must supply 6 arguments!\n"); return 1; } if ( (0 == strcmp (argv[3], "-")) && (0 == strcmp (argv[5], "-")) ) { fprintf (stderr, "Fatal: disabling both IPv4 and IPv6 makes no sense.\n"); return 1; } if (0 == access ("/sbin/iptables", X_OK)) sbin_iptables = "/sbin/iptables"; else if (0 == access ("/usr/sbin/iptables", X_OK)) sbin_iptables = "/usr/sbin/iptables"; else { fprintf (stderr, "Fatal: executable iptables not found in approved directories: %s\n", strerror (errno)); return 1; } if (0 == access ("/sbin/sysctl", X_OK)) sbin_sysctl = "/sbin/sysctl"; else if (0 == access ("/usr/sbin/sysctl", X_OK)) sbin_sysctl = "/usr/sbin/sysctl"; else { fprintf (stderr, "Fatal: executable sysctl not found in approved directories: %s\n", strerror (errno)); return 1; } strncpy (dev, argv[1], IFNAMSIZ); dev[IFNAMSIZ - 1] = '\0'; if (-1 == (fd_tun = init_tun (dev))) { fprintf (stderr, "Fatal: could not initialize tun-interface `%s' with IPv6 %s/%s and IPv4 %s/%s\n", dev, argv[3], argv[4], argv[5], argv[6]); return 1; } if (0 != strcmp (argv[3], "-")) { { const char *address = argv[3]; long prefix_len = atol (argv[4]); if ((prefix_len < 1) || (prefix_len > 127)) { fprintf (stderr, "Fatal: prefix_len out of range\n"); return 1; } set_address6 (dev, address, prefix_len); } { char *const sysctl_args[] = { "sysctl", "-w", "net.ipv6.conf.all.forwarding=1", NULL }; if (0 != fork_and_exec (sbin_sysctl, sysctl_args)) { fprintf (stderr, "Failed to enable IPv6 forwarding. Will continue anyway.\n"); } } } if (0 != strcmp (argv[5], "-")) { { const char *address = argv[5]; const char *mask = argv[6]; set_address4 (dev, address, mask); } { char *const sysctl_args[] = { "sysctl", "-w", "net.ipv4.ip_forward=1", NULL }; if (0 != fork_and_exec (sbin_sysctl, sysctl_args)) { fprintf (stderr, "Failed to enable IPv4 forwarding. Will continue anyway.\n"); } } if (0 != strcmp (argv[2], "%")) { char *const iptables_args[] = { "iptables", "-t", "nat", "-A", "POSTROUTING", "-o", argv[2], "-j", "MASQUERADE", NULL }; if (0 != fork_and_exec (sbin_iptables, iptables_args)) { fprintf (stderr, "Failed to enable IPv4 masquerading (NAT). Will continue anyway.\n"); } } } uid_t uid = getuid (); #ifdef HAVE_SETRESUID if (0 != setresuid (uid, uid, uid)) { fprintf (stderr, "Failed to setresuid: %s\n", strerror (errno)); global_ret = 2; goto cleanup; } #else if (0 != (setuid (uid) | seteuid (uid))) { fprintf (stderr, "Failed to setuid: %s\n", strerror (errno)); global_ret = 2; goto cleanup; } #endif if (SIG_ERR == signal (SIGPIPE, SIG_IGN)) { fprintf (stderr, "Failed to protect against SIGPIPE: %s\n", strerror (errno)); /* no exit, we might as well die with SIGPIPE should it ever happen */ } run (fd_tun); global_ret = 0; cleanup: close (fd_tun); return global_ret; } /* end of gnunet-helper-exit.c */