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- /*
- This file is part of GNUnet.
- Copyright (C) 2010, 2011, 2012 Christian Grothoff
- GNUnet is free software: you can redistribute it and/or modify it
- under the terms of the GNU Affero General Public License as published
- by the Free Software Foundation, either version 3 of the License,
- 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
- Affero General Public License for more details.
- You should have received a copy of the GNU Affero General Public License
- along with this program. If not, see <http://www.gnu.org/licenses/>.
- SPDX-License-Identifier: AGPL3.0-or-later
- */
- /**
- * @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 <linux/if_tun.h>
- /**
- * Need 'struct GNUNET_MessageHeader'.
- */
- #include "gnunet_crypto_lib.h"
- #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_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;
- uint32_t ifr6_prefixlen; /* __u32 in the original */
- int ifr6_ifindex;
- };
- #endif
- /**
- * Open '/dev/null' and make the result the given
- * file descriptor.
- *
- * @param target_fd desired FD to point to /dev/null
- * @param flags open flags (O_RDONLY, O_WRONLY)
- */
- static void
- open_dev_null (int target_fd,
- int flags)
- {
- int fd;
- fd = open ("/dev/null", flags);
- if (-1 == fd)
- abort ();
- if (fd == target_fd)
- return;
- if (-1 == dup2 (fd, target_fd))
- {
- (void) close (fd);
- abort ();
- }
- (void) close (fd);
- }
- /**
- * 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);
- open_dev_null (0, O_RDONLY);
- (void) close (1);
- open_dev_null (1, O_WRONLY);
- (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: "physical" interface name ("eth0"), or "-" to not setup NAT
- * and routing
- * 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 != strcmp (argv[2], "-"))
- {
- #ifdef IPTABLES
- if (0 == access (IPTABLES, X_OK))
- sbin_iptables = IPTABLES;
- else
- #endif
- 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;
- }
- #ifdef SYSCTL
- if (0 == access (SYSCTL, X_OK))
- sbin_sysctl = SYSCTL;
- else
- #endif
- 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);
- }
- if (0 != strcmp (argv[2], "-"))
- {
- 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);
- }
- if (0 != strcmp (argv[2], "-"))
- {
- {
- 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");
- }
- }
- {
- 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:
- (void) close (fd_tun);
- return global_ret;
- }
- /* end of gnunet-helper-exit.c */
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