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openssh/serverloop.c

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/*
* 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. */
/* Ignore any data if the client has closed stdin. */
if (fdin == -1)
break;
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 {
/* Keep the packets at reasonable size. */
if (len > packet_get_maxsize())
len = packet_get_maxsize();
}
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 {
/* Keep the packets at reasonable size. */
if (len > packet_get_maxsize())
len = packet_get_maxsize();
}
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 and there is enough buffer space to read
* from it, then read as much as is available and exit.
*/
if (child_terminated && packet_not_very_much_data_to_write())
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) {
verbose("Connection closed by remote host.");
fatal_cleanup();
}
/*
* 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) {
verbose("Read error from remote host: %.100s", strerror(errno));
fatal_cleanup();
}
/* 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) {
/* try again after a while */
max_time_milliseconds = 10;
} else {
/* Send it now. */
make_packets_from_stdout_data();
}
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 */
}
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