Start tor-fw-helper in the background, and log whatever it outputs

doc/tor.1.txt

@@ -873,6 +873,18 @@ is non-zero):
     specified in ORPort. (Default: 0.0.0.0) This directive can be specified
     multiple times to bind to multiple addresses/ports.
 
+**PortForwarding** **0**|**1**::
+    Attempt to automatically forward the DirPort and ORPort on a NAT router
+    connecting this Tor server to the Internet. If set, Tor will try both
+    NAT-PMP (common on Apple routers) and UPnP (common on routers from other
+    manufacturers). (Default: 0)
+
+**PortForwardingHelper** __filename__|__pathname__::
+    If PortForwarding is set, use this executable to configure the forwarding.
+    If set to a filename, the system path will be searched for the executable.
+    If set to a path, only the specified path will be executed.
+    (Default: tor-fw-helper)
+
 **PublishServerDescriptor** **0**|**1**|**v1**|**v2**|**v3**|**bridge**|**hidserv**,**...**::
     This option is only considered if you have an ORPort defined. You can
     choose multiple arguments, separated by commas.

src/common/util.c

@@ -14,6 +14,7 @@
 #define _GNU_SOURCE
 
 #include "orconfig.h"
+#define UTIL_PRIVATE
 #include "util.h"
 #include "torlog.h"
 #undef log
@@ -2877,3 +2878,400 @@ load_windows_system_library(const TCHAR *library_name)
   return LoadLibrary(path);
 }
 #endif
+
+/** Format child_state and saved_errno as a hex string placed in hex_errno.
+ * Called between fork and _exit, so must be signal-handler safe */
+void
+format_helper_exit_status(unsigned char child_state, int saved_errno,
+                          char *hex_errno)
+{
+  /* Convert errno to be unsigned for hex conversion */
+  unsigned int unsigned_errno;
+  char *cur;
+
+  /* If errno is negative, negate it */
+  if (saved_errno < 0) {
+    unsigned_errno = (unsigned int) -saved_errno;
+  } else {
+    unsigned_errno = (unsigned int) saved_errno;
+  }
+
+  /* Convert errno to hex (start before \n) */
+  cur = hex_errno + HEX_ERRNO_SIZE - 2;
+
+  do {
+    *cur-- = "0123456789ABCDEF"[unsigned_errno % 16];
+    unsigned_errno /= 16;
+  } while (unsigned_errno != 0 && cur >= hex_errno);
+
+  /* Add on the minus side if errno was negative */
+  if (saved_errno < 0)
+    *cur-- = '-';
+
+  /* Leave a gap */
+  *cur-- = '/';
+
+  /* Convert child_state to hex */
+  do {
+    *cur-- = "0123456789ABCDEF"[child_state % 16];
+    child_state /= 16;
+  } while (child_state != 0 && cur >= hex_errno);
+}
+
+/* Maximum number of file descriptors, if we cannot get it via sysconf() */
+#define DEFAULT_MAX_FD 256
+
+#define CHILD_STATE_INIT 0
+#define CHILD_STATE_PIPE 1
+#define CHILD_STATE_MAXFD 2
+#define CHILD_STATE_FORK 3
+#define CHILD_STATE_DUPOUT 4
+#define CHILD_STATE_DUPERR 5
+#define CHILD_STATE_REDIRECT 6
+#define CHILD_STATE_CLOSEFD 7
+#define CHILD_STATE_EXEC 8
+#define CHILD_STATE_FAILEXEC 9
+
+#define SPAWN_ERROR_MESSAGE "ERR: Failed to spawn background process - code "
+
+/** Start a program in the background. If <b>filename</b> contains a '/', then
+ * it will be treated as an absolute or relative path.  Otherwise the system
+ * path will be searched for <b>filename</b>. Returns pid on success, otherwise
+ * returns -1.
+ * Some parts of this code are based on the POSIX subprocess module from Python
+ */
+static int
+tor_spawn_background(const char *const filename, int *stdout_read,
+                     int *stderr_read, const char **argv)
+{
+  pid_t pid;
+  int stdout_pipe[2];
+  int stderr_pipe[2];
+  int fd, retval;
+  ssize_t nbytes;
+
+  const char *error_message = SPAWN_ERROR_MESSAGE;
+  size_t error_message_length;
+
+  /* Represents where in the process of spawning the program is;
+     this is used for printing out the error message */
+  unsigned char child_state = CHILD_STATE_INIT;
+
+  char hex_errno[HEX_ERRNO_SIZE];
+
+  static int max_fd = -1;
+
+  /* We do the strlen here because strlen() is not signal handler safe,
+     and we are not allowed to use unsafe functions between fork and exec */
+  error_message_length = strlen(error_message);
+
+  /* Fill hex_errno with spaces, and a trailing newline */
+  memset(hex_errno, ' ', sizeof(hex_errno) - 1);
+  hex_errno[sizeof(hex_errno) - 1] = '\n';
+
+  child_state = CHILD_STATE_PIPE;
+
+  /* Set up pipe for redirecting stdout and stderr of child */
+  retval = pipe(stdout_pipe);
+  if (-1 == retval) {
+    log_err(LD_GENERAL,
+      "Failed to set up pipe for stdout communication with child process: %s",
+       strerror(errno));
+    return -1;
+  }
+
+  retval = pipe(stderr_pipe);
+  if (-1 == retval) {
+    log_err(LD_GENERAL,
+      "Failed to set up pipe for stderr communication with child process: %s",
+      strerror(errno));
+    return -1;
+  }
+
+  child_state = CHILD_STATE_MAXFD;
+
+#ifdef _SC_OPEN_MAX
+  if (-1 != max_fd) {
+    max_fd = (int) sysconf(_SC_OPEN_MAX);
+    if (max_fd == -1)
+      max_fd = DEFAULT_MAX_FD;
+      log_warn(LD_GENERAL,
+               "Cannot find maximum file descriptor, assuming %d", max_fd);
+  }
+#else
+  max_fd = DEFAULT_MAX_FD;
+#endif
+
+  child_state = CHILD_STATE_FORK;
+
+  pid = fork();
+  if (0 == pid) {
+    /* In child */
+
+    child_state = CHILD_STATE_DUPOUT;
+
+    /* Link child stdout to the write end of the pipe */
+    retval = dup2(stdout_pipe[1], STDOUT_FILENO);
+    if (-1 == retval)
+        goto error;
+
+    child_state = CHILD_STATE_DUPERR;
+
+    /* Link child stderr to the write end of the pipe */
+    retval = dup2(stderr_pipe[1], STDERR_FILENO);
+    if (-1 == retval)
+        goto error;
+
+    child_state = CHILD_STATE_REDIRECT;
+
+    /* Link stdin to /dev/null */
+    fd = open("/dev/null", O_RDONLY);
+    if (fd != -1)
+      dup2(STDIN_FILENO, fd);
+    else
+      goto error;
+
+    child_state = CHILD_STATE_CLOSEFD;
+
+    /* Close all other fds, including the read end of the pipe */
+    /* TODO: use closefrom if available */
+    for (fd = STDERR_FILENO + 1; fd < max_fd; fd++)
+      close(fd);
+
+    child_state = CHILD_STATE_EXEC;
+
+    /* Call the requested program. We need the cast because
+       execvp doesn't define argv as const, even though it
+       does not modify the arguments */
+    execvp(filename, (char *const *) argv);
+
+    /* If we got here, the exec or open(/dev/null) failed */
+
+    child_state = CHILD_STATE_FAILEXEC;
+
+  error:
+    /* TODO: are we leaking fds from the pipe? */
+
+    format_helper_exit_status(child_state, errno, hex_errno);
+
+    /* Write the error message. GCC requires that we check the return
+       value, but there is nothing we can do if it fails */
+    nbytes = write(STDOUT_FILENO, error_message, error_message_length);
+    nbytes = write(STDOUT_FILENO, hex_errno, sizeof(hex_errno));
+
+    _exit(255);
+    return -1; /* Never reached, but avoids compiler warning */
+  }
+
+  /* In parent */
+
+  if (-1 == pid) {
+    log_err(LD_GENERAL, "Failed to fork child process: %s", strerror(errno));
+    close(stdout_pipe[0]);
+    close(stdout_pipe[1]);
+    close(stderr_pipe[0]);
+    close(stderr_pipe[1]);
+    return -1;
+  }
+
+  /* Return read end of the pipes to caller, and close write end */
+  *stdout_read = stdout_pipe[0];
+  retval = close(stdout_pipe[1]);
+
+  if (-1 == retval) {
+    log_err(LD_GENERAL,
+            "Failed to close write end of stdout pipe in parent process: %s",
+            strerror(errno));
+    /* Do not return -1, because the child is running, so the parent
+       needs to know about the pid in order to reap it later */
+  }
+
+  *stderr_read = stderr_pipe[0];
+  retval = close(stderr_pipe[1]);
+
+  if (-1 == retval) {
+    log_err(LD_GENERAL,
+            "Failed to close write end of stderr pipe in parent process: %s",
+            strerror(errno));
+    /* Do not return -1, because the child is running, so the parent
+       needs to know about the pid in order to reap it later */
+  }
+
+  return pid;
+}
+
+/** Read from stream, and send lines to log at the specified log level.
+ * Returns 1 if stream is closed normally, -1 if there is a error reading, and
+ * 0 otherwise. Handles lines from tor-fw-helper and
+ * tor_spawn_background() specially.
+ */
+static int
+log_from_pipe(FILE *stream, int severity, const char *executable,
+              int *child_status)
+{
+  char buf[256];
+
+  for (;;) {
+    char *retval;
+    retval = fgets(buf, sizeof(buf), stream);
+
+    if (NULL == retval) {
+      if (feof(stream)) {
+        /* Program has closed stream (probably it exited) */
+        /* TODO: check error */
+        fclose(stream);
+        return 1;
+      } else {
+        if (EAGAIN == errno) {
+          /* Nothing more to read, try again next time */
+          return 0;
+        } else {
+          /* There was a problem, abandon this child process */
+          fclose(stream);
+          return -1;
+        }
+      }
+    } else {
+      /* We have some data, log it and keep asking for more */
+      size_t len;
+
+      len = strlen(buf);
+      if (buf[len - 1] == '\n') {
+        /* Remove the trailing newline */
+        buf[len - 1] = '\0';
+      } else {
+        /* No newline; check whether we overflowed the buffer */
+        if (!feof(stream))
+          log_err(LD_GENERAL,
+                  "Line from port forwarding helper was truncated: %s", buf);
+          /* TODO: What to do with this error? */
+      }
+
+      /* Check if buf starts with SPAWN_ERROR_MESSAGE */
+      if (strstr(buf, SPAWN_ERROR_MESSAGE) == buf) {
+          /* Parse error message */
+          int retval, child_state, saved_errno;
+          retval = sscanf(buf, SPAWN_ERROR_MESSAGE "%d/%d",
+                          &child_state, &saved_errno);
+          if (retval == 2) {
+              log_err(LD_GENERAL,
+                "Failed to start child process \"%s\" in state %d: %s",
+                executable, child_state, strerror(saved_errno));
+              if (child_status)
+                  *child_status = 1;
+          } else {
+              /* Failed to parse message from child process, log it as error */
+              log_err(LD_GENERAL,
+                "Unexpected message from port forwarding helper \"%s\": %s",
+                executable, buf);
+          }
+      } else {
+          log_fn(severity, LD_GENERAL, "Port forwarding helper says: %s", buf);
+      }
+    }
+  }
+
+  /* We should never get here */
+  return -1;
+}
+
+void
+tor_check_port_forwarding(const char *filename, int dir_port, int or_port,
+                          time_t now)
+{
+
+/* When fw-helper succeeds, how long do we wait until running it again */
+#define TIME_TO_EXEC_FWHELPER_SUCCESS 300
+/* When fw-helper fails, how long do we wait until running it again */
+#define TIME_TO_EXEC_FWHELPER_FAIL 60
+
+  static int child_pid = -1;
+  static FILE *stdout_read = NULL;
+  static FILE *stderr_read = NULL;
+  static time_t time_to_run_helper = 0;
+  int stdout_status, stderr_status, retval;
+  const char *argv[10];
+  char s_dirport[6], s_orport[6];
+
+  tor_assert(filename);
+
+  /* Set up command line for tor-fw-helper */
+  snprintf(s_dirport, sizeof s_dirport, "%d", dir_port);
+  snprintf(s_orport, sizeof s_orport, "%d", or_port);
+
+  /* TODO: Allow different internal and external ports */
+  argv[0] = filename;
+  argv[1] = "--internal-or-port";
+  argv[2] = s_orport;
+  argv[3] = "--external-or-port";
+  argv[4] = s_orport;
+  argv[5] = "--internal-dir-port";
+  argv[6] = s_dirport;
+  argv[7] = "--external-dir-port";
+  argv[8] = s_dirport;
+  argv[9] = NULL;
+
+  /* Start the child, if it is not already running */
+  if (-1 == child_pid &&
+      time_to_run_helper < now) {
+    int fd_out, fd_err;
+
+    /* Assume tor-fw-helper will succeed, start it later*/
+    time_to_run_helper = now + TIME_TO_EXEC_FWHELPER_SUCCESS;
+
+    child_pid = tor_spawn_background(filename, &fd_out, &fd_err, argv);
+    if (child_pid < 0) {
+      log_err(LD_GENERAL, "Failed to start port forwarding helper %s",
+              filename);
+      child_pid = -1;
+      return;
+    }
+    /* Set stdout/stderr pipes to be non-blocking */
+    fcntl(fd_out, F_SETFL, O_NONBLOCK);
+    fcntl(fd_err, F_SETFL, O_NONBLOCK);
+    /* Open the buffered IO streams */
+    stdout_read = fdopen(fd_out, "r");
+    stderr_read = fdopen(fd_err, "r");
+
+    log_info(LD_GENERAL,
+      "Started port forwarding helper (%s) with pid %d", filename, child_pid);
+  }
+
+  /* If child is running, read from its stdout and stderr) */
+  if (child_pid > 0) {
+    /* Read from stdout/stderr and log result */
+    retval = 0;
+    stdout_status = log_from_pipe(stdout_read, LOG_INFO, filename, &retval);
+    stderr_status = log_from_pipe(stderr_read, LOG_ERR, filename, &retval);
+    if (retval) {
+      /* There was a problem in the child process */
+      time_to_run_helper = now + TIME_TO_EXEC_FWHELPER_FAIL;
+    }
+  
+    /* Combine the two statuses in order of severity */
+    if (-1 == stdout_status || -1 == stderr_status)
+      /* There was a failure */
+      retval = -1;
+    else if (1 == stdout_status || 1 == stderr_status)
+      /* stdout or stderr was closed */
+      retval = 1;
+    else
+      /* Both are fine */
+      retval = 0;
+  
+    /* If either pipe indicates a failure, act on it */
+    if (0 != retval) {
+      if (1 == retval) {
+        log_info(LD_GENERAL, "Port forwarding helper terminated");
+      } else {
+        log_err(LD_GENERAL, "Failed to read from port forwarding helper");
+      }
+  
+      /* TODO: The child might not actually be finished (maybe it failed or
+         closed stdout/stderr), so maybe we shouldn't start another? */
+      child_pid = -1;
+    }
+  }
+}
+
+

src/common/util.h

@@ -340,10 +340,25 @@ void start_daemon(void);
 void finish_daemon(const char *desired_cwd);
 void write_pidfile(char *filename);
 
+/* Port forwarding */
+void tor_check_port_forwarding(const char *filename,
+                               int dir_port, int or_port, time_t now);
+
 #ifdef MS_WINDOWS
 HANDLE load_windows_system_library(const TCHAR *library_name);
 #endif
 
+#ifdef UTIL_PRIVATE
+/* Prototypes for private functions only used by util.c (and unit tests) */
+void format_helper_exit_status(unsigned char child_state,
+                               int saved_errno, char *hex_errno);
+
+/* Space for hex values of child state, a slash, saved_errno (with
+   leading minus) and newline (no null) */
+#define HEX_ERRNO_SIZE (sizeof(char) * 2 + 1 + \
+                        1 + sizeof(int) * 2 + 1)
+#endif
+
 const char *libor_get_digests(void);
 
 #endif

src/or/config.c

@@ -317,6 +317,8 @@ static config_var_t _option_vars[] = {
   V(PerConnBWRate,               MEMUNIT,  "0"),
   V(PidFile,                     STRING,   NULL),
   V(TestingTorNetwork,           BOOL,     "0"),
+  V(PortForwarding,              BOOL,     "0"),
+  V(PortForwardingHelper,        FILENAME, "tor-fw-helper"),
   V(PreferTunneledDirConns,      BOOL,     "1"),
   V(ProtocolWarnings,            BOOL,     "0"),
   V(PublishServerDescriptor,     CSV,      "1"),

src/or/main.c

@@ -1026,6 +1026,7 @@ run_scheduled_events(time_t now)
   static time_t time_to_check_for_expired_networkstatus = 0;
   static time_t time_to_write_stats_files = 0;
   static time_t time_to_write_bridge_stats = 0;
+  static time_t time_to_check_port_forwarding = 0;
   static int should_init_bridge_stats = 1;
   static time_t time_to_retry_dns_init = 0;
   or_options_t *options = get_options();
@@ -1385,6 +1386,17 @@ run_scheduled_events(time_t now)
 #define BRIDGE_STATUSFILE_INTERVAL (30*60)
     time_to_write_bridge_status_file = now+BRIDGE_STATUSFILE_INTERVAL;
   }
+
+  if (time_to_check_port_forwarding < now &&
+      options->PortForwarding &&
+      server_mode(options)) {
+#define PORT_FORWARDING_CHECK_INTERVAL 5
+    tor_check_port_forwarding(options->PortForwardingHelper,
+                              options->DirPort,
+                              options->ORPort,
+                              now);
+    time_to_check_port_forwarding = now+PORT_FORWARDING_CHECK_INTERVAL;
+  }
 }
 
 /** Timer: used to invoke second_elapsed_callback() once per second. */

src/or/or.h

@@ -2772,6 +2772,10 @@ typedef struct {
                        * possible. */
   int PreferTunneledDirConns; /**< If true, avoid dirservers that don't
                                * support BEGIN_DIR, when possible. */
+  int PortForwarding; /**< If true, use NAT-PMP or UPnP to automatically
+                       * forward the DirPort and ORPort on the NAT device */
+  char *PortForwardingHelper; /** < Filename or full path of the port
+                                  forwarding helper executable */
   int AllowNonRFC953Hostnames; /**< If true, we allow connections to hostnames
                                 * with weird characters. */
   /** If true, we try resolving hostnames with weird characters. */

src/test/test_util.c

@@ -6,6 +6,7 @@
 #include "orconfig.h"
 #define CONTROL_PRIVATE
 #define MEMPOOL_PRIVATE
+#define UTIL_PRIVATE
 #include "or.h"
 #include "config.h"
 #include "control.h"
@@ -1208,6 +1209,45 @@ test_util_load_win_lib(void *ptr)
 }
 #endif
 
+static void
+clear_hex_errno(char *hex_errno)
+{
+  memset(hex_errno, ' ', HEX_ERRNO_SIZE - 2);
+  hex_errno[HEX_ERRNO_SIZE - 1] = '\n';
+  hex_errno[HEX_ERRNO_SIZE] = '\0';
+}
+
+static void
+test_util_exit_status(void *ptr)
+{
+  char hex_errno[HEX_ERRNO_SIZE + 1];
+
+  (void)ptr;
+
+  clear_hex_errno(hex_errno);
+  format_helper_exit_status(0, 0, hex_errno);
+  tt_str_op(hex_errno, ==, "         0/0\n");
+
+  clear_hex_errno(hex_errno);
+  format_helper_exit_status(0, 0x7FFFFFFF, hex_errno);
+  tt_str_op(hex_errno, ==, "  0/7FFFFFFF\n");
+
+  clear_hex_errno(hex_errno);
+  format_helper_exit_status(0xFF, -0x80000000, hex_errno);
+  tt_str_op(hex_errno, ==, "FF/-80000000\n");
+
+  clear_hex_errno(hex_errno);
+  format_helper_exit_status(0x7F, 0, hex_errno);
+  tt_str_op(hex_errno, ==, "        7F/0\n");
+
+  clear_hex_errno(hex_errno);
+  format_helper_exit_status(0x08, -0x242, hex_errno);
+  tt_str_op(hex_errno, ==, "      8/-242\n");
+
+ done:
+  ;
+}
+
 #define UTIL_LEGACY(name)                                               \
   { #name, legacy_test_helper, 0, &legacy_setup, test_util_ ## name }
 
@@ -1234,6 +1274,7 @@ struct testcase_t util_tests[] = {
 #ifdef MS_WINDOWS
   UTIL_TEST(load_win_lib, 0),
 #endif
+  UTIL_TEST(exit_status, 0),
   END_OF_TESTCASES
 };