Allow explicit UDP port option, confine ports to range 60000..61000

scripts/mosh

@@ -29,6 +29,8 @@ my $server = 'mosh-server';
 
 my $predict = undef;
 
+my $port_request = undef;
+
 my $usage =
 qq{Usage: $0 [options] [user@]host
     --client=PATH        mosh client on local machine  (default: "mosh-client")
@@ -38,6 +40,8 @@ qq{Usage: $0 [options] [user@]host
 -a  --predict=always     use local echo even on fast links
 -n  --predict=never      never use local echo
 
+-p  --port=NUM           server-side UDP port
+
 Please report bugs to mosh-devel\@mit.edu.
 Mosh home page: http://mosh.mit.edu\n};
 
@@ -55,8 +59,10 @@ sub predict_check {
 GetOptions( 'client=s' => \$client,
 	    'server=s' => \$server,
 	    'predict=s' => \$predict,
+	    'port=i' => \$port_request,
 	    'a' => sub { $predict = 'always' },
 	    'n' => sub { $predict = 'never' },
+	    'p=i' => \$port_request,
 	    'fake-proxy!' => \my $fake_proxy ) or die $usage;
 
 if ( defined $predict ) {
@@ -69,6 +75,16 @@ if ( defined $predict ) {
   predict_check( $predict, 0 );
 }
 
+if ( defined $port_request ) {
+  if ( $port_request =~ m{^[0-9]+$}
+       and $port_request >= 0
+       and $port_request <= 65535 ) {
+    # good port
+  } else {
+    die "$0: Server-side port ($port_request) must be within valid range [0..65535].\n";
+  }
+}
+
 delete $ENV{ 'MOSH_PREDICTION_DISPLAY' };
 
 if ( defined $fake_proxy ) {
@@ -133,7 +149,13 @@ if ( $pid == 0 ) { # child
   open STDERR, ">&", $pty_slave->fileno() or die;
   close $pty_slave;
 
-  my $s = q{sh -c 'exec "$@" "`set -- $SSH_CONNECTION; echo $3`"' -- } . $server;
+  my $s;
+  if ( defined $port_request ) {
+    $s = q{sh -c 'MOSH_PORT=$1; shift; MOSH_IP=`set -- $SSH_CONNECTION; echo $3`; exec "$@" $MOSH_IP $MOSH_PORT' -- } . $port_request . ' ' . $server;
+  } else {
+    # retain compatibility with older server when no port requested
+    $s = q{sh -c 'exec "$@" "`set -- $SSH_CONNECTION; echo $3`"' -- } . $server;
+  }
   exec 'ssh', '-S', 'none', '-o', "ProxyCommand=$0 --fake-proxy -- %h %p", '-t', $userhost, '--', $s;
   die "Cannot exec ssh: $!\n";
 } else { # server

src/crypto/crypto.cc

@@ -30,7 +30,7 @@ using namespace Crypto;
 
 const char rdev[] = "/dev/urandom";
 
-long int myatoi( char *str )
+long int myatoi( const char *str )
 {
   char *end;
 

src/crypto/crypto.h

@@ -26,7 +26,7 @@
 
 using std::string;
 
-long int myatoi( char *str );
+long int myatoi( const char *str );
 
 namespace Crypto {
   class CryptoException {

src/examples/ntester.cc

@@ -48,7 +48,7 @@ int main( int argc, char *argv[] )
       
       n = new Transport<UserStream, UserStream>( me, remote, key, ip, port );
     } else {
-      n = new Transport<UserStream, UserStream>( me, remote, NULL );
+      n = new Transport<UserStream, UserStream>( me, remote, NULL, NULL );
     }
   } catch ( CryptoException e ) {
     fprintf( stderr, "Fatal error: %s\n", e.text.c_str() );

src/frontend/mosh-server.cc

@@ -62,17 +62,23 @@ void serve( int host_fd,
 	    Terminal::Complete &terminal,
 	    ServerConnection &network );
 
+int run_server( const char *desired_ip, const char *desired_port );
+
 using namespace std;
 
 int main( int argc, char *argv[] )
 {
   char *desired_ip = NULL;
+  char *desired_port = NULL;
   if ( argc == 1 ) {
     desired_ip = NULL;
   } else if ( argc == 2 ) {
     desired_ip = argv[ 1 ];
+  } else if ( argc == 3 ) {
+    desired_ip = argv[ 1 ];
+    desired_port = argv[ 2 ];
   } else {
-    fprintf( stderr, "Usage: %s [LOCALADDR]\n", argv[ 0 ] );
+    fprintf( stderr, "Usage: %s [LOCALADDR] [PORT]\n", argv[ 0 ] );
     exit( 1 );
   }
 
@@ -88,6 +94,20 @@ int main( int argc, char *argv[] )
     exit( 1 );
   }
 
+  try {
+    return run_server( desired_ip, desired_port );
+  } catch ( Network::NetworkException e ) {
+    fprintf( stderr, "Network exception: %s: %s\n",
+	     e.function.c_str(), strerror( e.the_errno ) );
+    return 1;
+  } catch ( Crypto::CryptoException e ) {
+    fprintf( stderr, "Crypto exception: %s\n",
+	     e.text.c_str() );
+    return 1;
+  }
+}
+
+int run_server( const char *desired_ip, const char *desired_port ) {
   /* get initial window size */
   struct winsize window_size;
   if ( ioctl( STDIN_FILENO, TIOCGWINSZ, &window_size ) < 0 ) {
@@ -100,7 +120,7 @@ int main( int argc, char *argv[] )
 
   /* open network */
   Network::UserStream blank;
-  ServerConnection network( terminal, blank, desired_ip );
+  ServerConnection network( terminal, blank, desired_ip, desired_port );
 
   /* network.set_verbose(); */
 
@@ -131,7 +151,7 @@ int main( int argc, char *argv[] )
     _exit( 0 );
   }
 
-  fprintf( stderr, "[mosh-server detached, pid=%d.]\n", (int)getpid() );
+  fprintf( stderr, "[mosh-server detached, pid = %d]\n", (int)getpid() );
 
   int master;
 

src/network/network.cc

@@ -115,7 +115,7 @@ void Connection::setup( void )
 #endif
 }
 
-Connection::Connection( const char *desired_ip ) /* server */
+Connection::Connection( const char *desired_ip, const char *desired_port ) /* server */
   : sock( -1 ),
     has_remote_addr( false ),
     remote_addr(),
@@ -134,30 +134,92 @@ Connection::Connection( const char *desired_ip ) /* server */
 {
   setup();
 
-  /* Attempt to bind free local port, with
-     address client used to connect to us.
+  /* The mosh wrapper always gives an IP request, in order
+     to deal with multihomed servers. The port is optional. */
 
-     This usage does not seem to be endorsed by POSIX. */
+  /* If an IP request is given, we try to bind to that IP, but we also
+     try INADDR_ANY. If a port request is given, we bind only to that port. */
 
-  struct sockaddr_in local_addr;
-  local_addr.sin_family = AF_INET;
-  local_addr.sin_port = htons( 0 );
-  if ( desired_ip
-       && inet_aton( desired_ip, &local_addr.sin_addr )
-       && (bind( sock, (sockaddr *)&local_addr, sizeof( local_addr ) ) == 0) ) {
-    return;
+  /* convert port number */
+  long int desired_port_no = 0;
+
+  if ( desired_port ) {
+    char *end;
+    errno = 0;
+    desired_port_no = strtol( desired_port, &end, 10 );
+    if ( (errno != 0) || (end != desired_port + strlen( desired_port )) ) {
+      throw NetworkException( "Invalid port number", errno );
+    }
   }
 
+  if ( (desired_port_no < 0) || (desired_port_no > 65535) ) {
+    throw NetworkException( "Port number outside valid range [0..65535]", 0 );
+  }
+
+  /* convert desired IP */
+  uint32_t desired_ip_addr = INADDR_ANY;
+
   if ( desired_ip ) {
-    fprintf( stderr, "Could not bind to desired local address %s.\n", desired_ip );
+    struct in_addr sin_addr;
+    if ( inet_aton( desired_ip, &sin_addr ) == 0 ) {
+      throw NetworkException( "Invalid IP address", errno );
+    }
+    desired_ip_addr = sin_addr.s_addr;
   }
 
-  /* Could not bind to that IP (maybe we are behind NAT).
-     Try again with any IP. */
-  local_addr.sin_addr.s_addr = INADDR_ANY;
-  if ( bind( sock, (sockaddr *)&local_addr, sizeof( local_addr ) ) < 0 ) {
-    throw NetworkException( "bind", errno );
+  /* try to bind to desired IP first */
+  if ( desired_ip_addr != INADDR_ANY ) {
+    try {
+      if ( try_bind( sock, desired_ip_addr, desired_port_no ) ) { return; }
+    } catch ( NetworkException e ) {
+      struct in_addr sin_addr;
+      sin_addr.s_addr = desired_ip_addr;
+      fprintf( stderr, "Error binding to IP %s: %s: %s\n",
+	       inet_ntoa( sin_addr ),
+	       e.function.c_str(), strerror( e.the_errno ) );
+    }
   }
+
+  /* now try any local interface */
+  try {
+    if ( try_bind( sock, INADDR_ANY, desired_port_no ) ) { return; }
+  } catch ( NetworkException e ) {
+    fprintf( stderr, "Error binding to any interface: %s: %s\n",
+	     e.function.c_str(), strerror( e.the_errno ) );
+    throw; /* this time it's fatal */
+  }
+
+  assert( false );
+  throw NetworkException( "Could not bind", errno );
+}
+
+bool Connection::try_bind( int socket, uint32_t s_addr, int port )
+{
+  struct sockaddr_in local_addr;
+  local_addr.sin_family = AF_INET;
+  local_addr.sin_addr.s_addr = s_addr;
+
+  int search_low = PORT_RANGE_LOW, search_high = PORT_RANGE_HIGH;
+
+  if ( port != 0 ) { /* port preference */
+    search_low = search_high = port;
+  }
+
+  for ( int i = search_low; i <= search_high; i++ ) {
+    local_addr.sin_port = htons( i );
+
+    if ( bind( socket, (sockaddr *)&local_addr, sizeof( local_addr ) ) == 0 ) {
+      fprintf( stderr, "Server now bound to %s:%d\n",
+	       inet_ntoa( local_addr.sin_addr ),
+	       ntohs( local_addr.sin_port ) );
+      return true;
+    } else if ( i == search_high ) { /* last port to search */
+      throw NetworkException( "bind", errno );
+    }
+  }
+
+  assert( false );
+  return false;
 }
 
 Connection::Connection( const char *key_str, const char *ip, int port ) /* client */
@@ -266,10 +328,10 @@ string Connection::recv( void )
     /* auto-adjust to remote host */
     has_remote_addr = true;
 
-    if ( (remote_addr.sin_addr.s_addr != packet_remote_addr.sin_addr.s_addr)
-	 || (remote_addr.sin_port != packet_remote_addr.sin_port) ) {
-      remote_addr = packet_remote_addr;
-      if ( server ) {
+    if ( server ) { /* only client can roam */
+      if ( (remote_addr.sin_addr.s_addr != packet_remote_addr.sin_addr.s_addr)
+	   || (remote_addr.sin_port != packet_remote_addr.sin_port) ) {
+	remote_addr = packet_remote_addr;
 	fprintf( stderr, "Server now attached to client at %s:%d\n",
 		 inet_ntoa( remote_addr.sin_addr ),
 		 ntohs( remote_addr.sin_port ) );

src/network/network.h

@@ -74,6 +74,11 @@ namespace Network {
     static const uint64_t MIN_RTO = 50; /* ms */
     static const uint64_t MAX_RTO = 1000; /* ms */
 
+    static const int PORT_RANGE_LOW  = 60001;
+    static const int PORT_RANGE_HIGH = 60999;
+
+    static bool try_bind( int socket, uint32_t s_addr, int port );
+
     int sock;
     bool has_remote_addr;
     struct sockaddr_in remote_addr;
@@ -100,7 +105,7 @@ namespace Network {
     Packet new_packet( string &s_payload );
 
   public:
-    Connection( const char *desired_ip ); /* server */
+    Connection( const char *desired_ip, const char *desired_port ); /* server */
     Connection( const char *key_str, const char *ip, int port ); /* client */
     
     void send( string s );

src/network/networktransport.cc

@@ -28,8 +28,8 @@ using namespace std;
 
 template <class MyState, class RemoteState>
 Transport<MyState, RemoteState>::Transport( MyState &initial_state, RemoteState &initial_remote,
-					    const char *desired_ip )
-  : connection( desired_ip ),
+					    const char *desired_ip, const char *desired_port )
+  : connection( desired_ip, desired_port ),
     sender( &connection, initial_state ),
     received_states( 1, TimestampedState<RemoteState>( timestamp(), 0, initial_remote ) ),
     last_receiver_state( initial_remote ),

src/network/networktransport.h

@@ -51,7 +51,8 @@ namespace Network {
     bool verbose;
 
   public:
-    Transport( MyState &initial_state, RemoteState &initial_remote, const char *desired_ip );
+    Transport( MyState &initial_state, RemoteState &initial_remote,
+	       const char *desired_ip, const char *desired_port );
     Transport( MyState &initial_state, RemoteState &initial_remote,
 	       const char *key_str, const char *ip, int port );