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Diffstat (limited to 'serverloop.c')
| -rw-r--r-- | serverloop.c | 644 |
1 files changed, 644 insertions, 0 deletions
diff --git a/serverloop.c b/serverloop.c new file mode 100644 index 00000000..552c69c2 --- /dev/null +++ b/serverloop.c @@ -0,0 +1,644 @@ +/* + +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*/ +} + |