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+/*
+
+serverloop.c
+
+Author: Tatu Ylonen <ylo@cs.hut.fi>
+
+Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
+ All rights reserved
+
+Created: Sun Sep 10 00:30:37 1995 ylo
+
+Server main loop for handling the interactive session.
+
+*/
+
+#include "includes.h"
+#include "xmalloc.h"
+#include "ssh.h"
+#include "packet.h"
+#include "buffer.h"
+#include "servconf.h"
+#include "pty.h"
+
+static Buffer stdin_buffer; /* Buffer for stdin data. */
+static Buffer stdout_buffer; /* Buffer for stdout data. */
+static Buffer stderr_buffer; /* Buffer for stderr data. */
+static int fdin; /* Descriptor for stdin (for writing) */
+static int fdout; /* Descriptor for stdout (for reading);
+ May be same number as fdin. */
+static int fderr; /* Descriptor for stderr. May be -1. */
+static long stdin_bytes = 0; /* Number of bytes written to stdin. */
+static long stdout_bytes = 0; /* Number of stdout bytes sent to client. */
+static long stderr_bytes = 0; /* Number of stderr bytes sent to client. */
+static long fdout_bytes = 0; /* Number of stdout bytes read from program. */
+static int stdin_eof = 0; /* EOF message received from client. */
+static int fdout_eof = 0; /* EOF encountered reading from fdout. */
+static int fderr_eof = 0; /* EOF encountered readung from fderr. */
+static int connection_in; /* Connection to client (input). */
+static int connection_out; /* Connection to client (output). */
+static unsigned int buffer_high;/* "Soft" max buffer size. */
+static int max_fd; /* Max file descriptor number for select(). */
+
+/* This SIGCHLD kludge is used to detect when the child exits. The server
+ will exit after that, as soon as forwarded connections have terminated. */
+
+static int child_pid; /* Pid of the child. */
+static volatile int child_terminated; /* The child has terminated. */
+static volatile int child_wait_status; /* Status from wait(). */
+
+void sigchld_handler(int sig)
+{
+ int save_errno = errno;
+ int wait_pid;
+ debug("Received SIGCHLD.");
+ wait_pid = wait((int *)&child_wait_status);
+ if (wait_pid != -1)
+ {
+ if (wait_pid != child_pid)
+ error("Strange, got SIGCHLD and wait returned pid %d but child is %d",
+ wait_pid, child_pid);
+ if (WIFEXITED(child_wait_status) ||
+ WIFSIGNALED(child_wait_status))
+ child_terminated = 1;
+ }
+ signal(SIGCHLD, sigchld_handler);
+ errno = save_errno;
+}
+
+/* Process any buffered packets that have been received from the client. */
+
+void process_buffered_input_packets()
+{
+ int type;
+ char *data;
+ unsigned int data_len;
+ int row, col, xpixel, ypixel;
+ int payload_len;
+
+ /* Process buffered packets from the client. */
+ while ((type = packet_read_poll(&payload_len)) != SSH_MSG_NONE)
+ {
+ switch (type)
+ {
+ case SSH_CMSG_STDIN_DATA:
+ /* Stdin data from the client. Append it to the buffer. */
+ if (fdin == -1)
+ break; /* Ignore any data if the client has closed stdin. */
+ data = packet_get_string(&data_len);
+ packet_integrity_check(payload_len, (4 + data_len), type);
+ buffer_append(&stdin_buffer, data, data_len);
+ memset(data, 0, data_len);
+ xfree(data);
+ break;
+
+ case SSH_CMSG_EOF:
+ /* Eof from the client. The stdin descriptor to the program
+ will be closed when all buffered data has drained. */
+ debug("EOF received for stdin.");
+ packet_integrity_check(payload_len, 0, type);
+ stdin_eof = 1;
+ break;
+
+ case SSH_CMSG_WINDOW_SIZE:
+ debug("Window change received.");
+ packet_integrity_check(payload_len, 4*4, type);
+ row = packet_get_int();
+ col = packet_get_int();
+ xpixel = packet_get_int();
+ ypixel = packet_get_int();
+ if (fdin != -1)
+ pty_change_window_size(fdin, row, col, xpixel, ypixel);
+ break;
+
+ case SSH_MSG_PORT_OPEN:
+ debug("Received port open request.");
+ channel_input_port_open(payload_len);
+ break;
+
+ case SSH_MSG_CHANNEL_OPEN_CONFIRMATION:
+ debug("Received channel open confirmation.");
+ packet_integrity_check(payload_len, 4 + 4, type);
+ channel_input_open_confirmation();
+ break;
+
+ case SSH_MSG_CHANNEL_OPEN_FAILURE:
+ debug("Received channel open failure.");
+ packet_integrity_check(payload_len, 4, type);
+ channel_input_open_failure();
+ break;
+
+ case SSH_MSG_CHANNEL_DATA:
+ channel_input_data(payload_len);
+ break;
+
+ case SSH_MSG_CHANNEL_CLOSE:
+ debug("Received channel close.");
+ packet_integrity_check(payload_len, 4, type);
+ channel_input_close();
+ break;
+
+ case SSH_MSG_CHANNEL_CLOSE_CONFIRMATION:
+ debug("Received channel close confirmation.");
+ packet_integrity_check(payload_len, 4, type);
+ channel_input_close_confirmation();
+ break;
+
+ default:
+ /* In this phase, any unexpected messages cause a protocol
+ error. This is to ease debugging; also, since no
+ confirmations are sent messages, unprocessed unknown
+ messages could cause strange problems. Any compatible
+ protocol extensions must be negotiated before entering the
+ interactive session. */
+ packet_disconnect("Protocol error during session: type %d",
+ type);
+ }
+ }
+}
+
+/* Make packets from buffered stderr data, and buffer it for sending
+ to the client. */
+
+void make_packets_from_stderr_data()
+{
+ int len;
+
+ /* Send buffered stderr data to the client. */
+ while (buffer_len(&stderr_buffer) > 0 &&
+ packet_not_very_much_data_to_write())
+ {
+ len = buffer_len(&stderr_buffer);
+ if (packet_is_interactive())
+ {
+ if (len > 512)
+ len = 512;
+ }
+ else
+ {
+ if (len > 32768)
+ len = 32768; /* Keep the packets at reasonable size. */
+ }
+ packet_start(SSH_SMSG_STDERR_DATA);
+ packet_put_string(buffer_ptr(&stderr_buffer), len);
+ packet_send();
+ buffer_consume(&stderr_buffer, len);
+ stderr_bytes += len;
+ }
+}
+
+/* Make packets from buffered stdout data, and buffer it for sending to the
+ client. */
+
+void make_packets_from_stdout_data()
+{
+ int len;
+
+ /* Send buffered stdout data to the client. */
+ while (buffer_len(&stdout_buffer) > 0 &&
+ packet_not_very_much_data_to_write())
+ {
+ len = buffer_len(&stdout_buffer);
+ if (packet_is_interactive())
+ {
+ if (len > 512)
+ len = 512;
+ }
+ else
+ {
+ if (len > 32768)
+ len = 32768; /* Keep the packets at reasonable size. */
+ }
+ packet_start(SSH_SMSG_STDOUT_DATA);
+ packet_put_string(buffer_ptr(&stdout_buffer), len);
+ packet_send();
+ buffer_consume(&stdout_buffer, len);
+ stdout_bytes += len;
+ }
+}
+
+/* Sleep in select() until we can do something. This will initialize the
+ select masks. Upon return, the masks will indicate which descriptors
+ have data or can accept data. Optionally, a maximum time can be specified
+ for the duration of the wait (0 = infinite). */
+
+void wait_until_can_do_something(fd_set *readset, fd_set *writeset,
+ unsigned int max_time_milliseconds)
+{
+ struct timeval tv, *tvp;
+ int ret;
+
+ /* When select fails we restart from here. */
+retry_select:
+
+ /* Initialize select() masks. */
+ FD_ZERO(readset);
+
+ /* Read packets from the client unless we have too much buffered stdin
+ or channel data. */
+ if (buffer_len(&stdin_buffer) < 4096 &&
+ channel_not_very_much_buffered_data())
+ FD_SET(connection_in, readset);
+
+ /* If there is not too much data already buffered going to the client,
+ try to get some more data from the program. */
+ if (packet_not_very_much_data_to_write())
+ {
+ if (!fdout_eof)
+ FD_SET(fdout, readset);
+ if (!fderr_eof)
+ FD_SET(fderr, readset);
+ }
+
+ FD_ZERO(writeset);
+
+ /* Set masks for channel descriptors. */
+ channel_prepare_select(readset, writeset);
+
+ /* If we have buffered packet data going to the client, mark that
+ descriptor. */
+ if (packet_have_data_to_write())
+ FD_SET(connection_out, writeset);
+
+ /* If we have buffered data, try to write some of that data to the
+ program. */
+ if (fdin != -1 && buffer_len(&stdin_buffer) > 0)
+ FD_SET(fdin, writeset);
+
+ /* Update the maximum descriptor number if appropriate. */
+ if (channel_max_fd() > max_fd)
+ max_fd = channel_max_fd();
+
+ /* If child has terminated, read as much as is available and then exit. */
+ if (child_terminated)
+ if (max_time_milliseconds == 0)
+ max_time_milliseconds = 100;
+
+ if (max_time_milliseconds == 0)
+ tvp = NULL;
+ else
+ {
+ tv.tv_sec = max_time_milliseconds / 1000;
+ tv.tv_usec = 1000 * (max_time_milliseconds % 1000);
+ tvp = &tv;
+ }
+
+ /* Wait for something to happen, or the timeout to expire. */
+ ret = select(max_fd + 1, readset, writeset, NULL, tvp);
+
+ if (ret < 0)
+ {
+ if (errno != EINTR)
+ error("select: %.100s", strerror(errno));
+ else
+ goto retry_select;
+ }
+}
+
+/* Processes input from the client and the program. Input data is stored
+ in buffers and processed later. */
+
+void process_input(fd_set *readset)
+{
+ int len;
+ char buf[16384];
+
+ /* Read and buffer any input data from the client. */
+ if (FD_ISSET(connection_in, readset))
+ {
+ len = read(connection_in, buf, sizeof(buf));
+ if (len == 0)
+ fatal("Connection closed by remote host.");
+
+ /* There is a kernel bug on Solaris that causes select to sometimes
+ wake up even though there is no data available. */
+ if (len < 0 && errno == EAGAIN)
+ len = 0;
+
+ if (len < 0)
+ fatal("Read error from remote host: %.100s", strerror(errno));
+
+ /* Buffer any received data. */
+ packet_process_incoming(buf, len);
+ }
+
+ /* Read and buffer any available stdout data from the program. */
+ if (!fdout_eof && FD_ISSET(fdout, readset))
+ {
+ len = read(fdout, buf, sizeof(buf));
+ if (len <= 0)
+ fdout_eof = 1;
+ else
+ {
+ buffer_append(&stdout_buffer, buf, len);
+ fdout_bytes += len;
+ }
+ }
+
+ /* Read and buffer any available stderr data from the program. */
+ if (!fderr_eof && FD_ISSET(fderr, readset))
+ {
+ len = read(fderr, buf, sizeof(buf));
+ if (len <= 0)
+ fderr_eof = 1;
+ else
+ buffer_append(&stderr_buffer, buf, len);
+ }
+}
+
+/* Sends data from internal buffers to client program stdin. */
+
+void process_output(fd_set *writeset)
+{
+ int len;
+
+ /* Write buffered data to program stdin. */
+ if (fdin != -1 && FD_ISSET(fdin, writeset))
+ {
+ len = write(fdin, buffer_ptr(&stdin_buffer),
+ buffer_len(&stdin_buffer));
+ if (len <= 0)
+ {
+#ifdef USE_PIPES
+ close(fdin);
+#else
+ if (fdout == -1)
+ close(fdin);
+ else
+ shutdown(fdin, SHUT_WR); /* We will no longer send. */
+#endif
+ fdin = -1;
+ }
+ else
+ {
+ /* Successful write. Consume the data from the buffer. */
+ buffer_consume(&stdin_buffer, len);
+ /* Update the count of bytes written to the program. */
+ stdin_bytes += len;
+ }
+ }
+
+ /* Send any buffered packet data to the client. */
+ if (FD_ISSET(connection_out, writeset))
+ packet_write_poll();
+}
+
+/* Wait until all buffered output has been sent to the client.
+ This is used when the program terminates. */
+
+void drain_output()
+{
+ /* Send any buffered stdout data to the client. */
+ if (buffer_len(&stdout_buffer) > 0)
+ {
+ packet_start(SSH_SMSG_STDOUT_DATA);
+ packet_put_string(buffer_ptr(&stdout_buffer),
+ buffer_len(&stdout_buffer));
+ packet_send();
+ /* Update the count of sent bytes. */
+ stdout_bytes += buffer_len(&stdout_buffer);
+ }
+
+ /* Send any buffered stderr data to the client. */
+ if (buffer_len(&stderr_buffer) > 0)
+ {
+ packet_start(SSH_SMSG_STDERR_DATA);
+ packet_put_string(buffer_ptr(&stderr_buffer),
+ buffer_len(&stderr_buffer));
+ packet_send();
+ /* Update the count of sent bytes. */
+ stderr_bytes += buffer_len(&stderr_buffer);
+ }
+
+ /* Wait until all buffered data has been written to the client. */
+ packet_write_wait();
+}
+
+/* Performs the interactive session. This handles data transmission between
+ the client and the program. Note that the notion of stdin, stdout, and
+ stderr in this function is sort of reversed: this function writes to
+ stdin (of the child program), and reads from stdout and stderr (of the
+ child program). */
+
+void server_loop(int pid, int fdin_arg, int fdout_arg, int fderr_arg)
+{
+ int wait_status, wait_pid; /* Status and pid returned by wait(). */
+ int waiting_termination = 0; /* Have displayed waiting close message. */
+ unsigned int max_time_milliseconds;
+ unsigned int previous_stdout_buffer_bytes;
+ unsigned int stdout_buffer_bytes;
+ int type;
+
+ debug("Entering interactive session.");
+
+ /* Initialize the SIGCHLD kludge. */
+ child_pid = pid;
+ child_terminated = 0;
+ signal(SIGCHLD, sigchld_handler);
+
+ /* Initialize our global variables. */
+ fdin = fdin_arg;
+ fdout = fdout_arg;
+ fderr = fderr_arg;
+ connection_in = packet_get_connection_in();
+ connection_out = packet_get_connection_out();
+
+ previous_stdout_buffer_bytes = 0;
+
+ /* Set approximate I/O buffer size. */
+ if (packet_is_interactive())
+ buffer_high = 4096;
+ else
+ buffer_high = 64 * 1024;
+
+ /* Initialize max_fd to the maximum of the known file descriptors. */
+ max_fd = fdin;
+ if (fdout > max_fd)
+ max_fd = fdout;
+ if (fderr != -1 && fderr > max_fd)
+ max_fd = fderr;
+ if (connection_in > max_fd)
+ max_fd = connection_in;
+ if (connection_out > max_fd)
+ max_fd = connection_out;
+
+ /* Initialize Initialize buffers. */
+ buffer_init(&stdin_buffer);
+ buffer_init(&stdout_buffer);
+ buffer_init(&stderr_buffer);
+
+ /* If we have no separate fderr (which is the case when we have a pty - there
+ we cannot make difference between data sent to stdout and stderr),
+ indicate that we have seen an EOF from stderr. This way we don\'t
+ need to check the descriptor everywhere. */
+ if (fderr == -1)
+ fderr_eof = 1;
+
+ /* Main loop of the server for the interactive session mode. */
+ for (;;)
+ {
+ fd_set readset, writeset;
+
+ /* Process buffered packets from the client. */
+ process_buffered_input_packets();
+
+ /* If we have received eof, and there is no more pending input data,
+ cause a real eof by closing fdin. */
+ if (stdin_eof && fdin != -1 && buffer_len(&stdin_buffer) == 0)
+ {
+#ifdef USE_PIPES
+ close(fdin);
+#else
+ if (fdout == -1)
+ close(fdin);
+ else
+ shutdown(fdin, SHUT_WR); /* We will no longer send. */
+#endif
+ fdin = -1;
+ }
+
+ /* Make packets from buffered stderr data to send to the client. */
+ make_packets_from_stderr_data();
+
+ /* Make packets from buffered stdout data to send to the client.
+ If there is very little to send, this arranges to not send them
+ now, but to wait a short while to see if we are getting more data.
+ This is necessary, as some systems wake up readers from a pty after
+ each separate character. */
+ max_time_milliseconds = 0;
+ stdout_buffer_bytes = buffer_len(&stdout_buffer);
+ if (stdout_buffer_bytes != 0 && stdout_buffer_bytes < 256 &&
+ stdout_buffer_bytes != previous_stdout_buffer_bytes)
+ max_time_milliseconds = 10; /* try again after a while */
+ else
+ make_packets_from_stdout_data(); /* Send it now. */
+ previous_stdout_buffer_bytes = buffer_len(&stdout_buffer);
+
+ /* Send channel data to the client. */
+ if (packet_not_very_much_data_to_write())
+ channel_output_poll();
+
+ /* Bail out of the loop if the program has closed its output descriptors,
+ and we have no more data to send to the client, and there is no
+ pending buffered data. */
+ if (fdout_eof && fderr_eof && !packet_have_data_to_write() &&
+ buffer_len(&stdout_buffer) == 0 && buffer_len(&stderr_buffer) == 0)
+ {
+ if (!channel_still_open())
+ goto quit;
+ if (!waiting_termination)
+ {
+ const char *s =
+ "Waiting for forwarded connections to terminate...\r\n";
+ char *cp;
+ waiting_termination = 1;
+ buffer_append(&stderr_buffer, s, strlen(s));
+
+ /* Display list of open channels. */
+ cp = channel_open_message();
+ buffer_append(&stderr_buffer, cp, strlen(cp));
+ xfree(cp);
+ }
+ }
+
+ /* Sleep in select() until we can do something. */
+ wait_until_can_do_something(&readset, &writeset,
+ max_time_milliseconds);
+
+ /* Process any channel events. */
+ channel_after_select(&readset, &writeset);
+
+ /* Process input from the client and from program stdout/stderr. */
+ process_input(&readset);
+
+ /* Process output to the client and to program stdin. */
+ process_output(&writeset);
+ }
+
+ quit:
+ /* Cleanup and termination code. */
+
+ /* Wait until all output has been sent to the client. */
+ drain_output();
+
+ debug("End of interactive session; stdin %ld, stdout (read %ld, sent %ld), stderr %ld bytes.",
+ stdin_bytes, fdout_bytes, stdout_bytes, stderr_bytes);
+
+ /* Free and clear the buffers. */
+ buffer_free(&stdin_buffer);
+ buffer_free(&stdout_buffer);
+ buffer_free(&stderr_buffer);
+
+ /* Close the file descriptors. */
+ if (fdout != -1)
+ close(fdout);
+ fdout = -1;
+ fdout_eof = 1;
+ if (fderr != -1)
+ close(fderr);
+ fderr = -1;
+ fderr_eof = 1;
+ if (fdin != -1)
+ close(fdin);
+ fdin = -1;
+
+ /* Stop listening for channels; this removes unix domain sockets. */
+ channel_stop_listening();
+
+ /* Wait for the child to exit. Get its exit status. */
+ wait_pid = wait(&wait_status);
+ if (wait_pid < 0)
+ {
+ /* It is possible that the wait was handled by SIGCHLD handler. This
+ may result in either: this call returning with EINTR, or: this
+ call returning ECHILD. */
+ if (child_terminated)
+ wait_status = child_wait_status;
+ else
+ packet_disconnect("wait: %.100s", strerror(errno));
+ }
+ else
+ {
+ /* Check if it matches the process we forked. */
+ if (wait_pid != pid)
+ error("Strange, wait returned pid %d, expected %d", wait_pid, pid);
+ }
+
+ /* We no longer want our SIGCHLD handler to be called. */
+ signal(SIGCHLD, SIG_DFL);
+
+ /* Check if it exited normally. */
+ if (WIFEXITED(wait_status))
+ {
+ /* Yes, normal exit. Get exit status and send it to the client. */
+ debug("Command exited with status %d.", WEXITSTATUS(wait_status));
+ packet_start(SSH_SMSG_EXITSTATUS);
+ packet_put_int(WEXITSTATUS(wait_status));
+ packet_send();
+ packet_write_wait();
+
+ /* Wait for exit confirmation. Note that there might be other
+ packets coming before it; however, the program has already died
+ so we just ignore them. The client is supposed to respond with
+ the confirmation when it receives the exit status. */
+ do
+ {
+ int plen;
+ type = packet_read(&plen);
+ }
+ while (type != SSH_CMSG_EXIT_CONFIRMATION);
+
+ debug("Received exit confirmation.");
+ return;
+ }
+
+ /* Check if the program terminated due to a signal. */
+ if (WIFSIGNALED(wait_status))
+ packet_disconnect("Command terminated on signal %d.",
+ WTERMSIG(wait_status));
+
+ /* Some weird exit cause. Just exit. */
+ packet_disconnect("wait returned status %04x.", wait_status);
+ /*NOTREACHED*/
+}
+