/**
* mds — A micro-display server
* Copyright © 2014, 2015, 2016 Mattias Andrée (maandree@member.fsf.org)
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include "mds-vt.h"
#include <libmdsserver/config.h>
#include <libmdsserver/macros.h>
#include <libmdsserver/util.h>
#include <libmdsserver/mds-message.h>
#include <errno.h>
#include <inttypes.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <linux/kd.h>
#include <limits.h>
#include <fcntl.h>
#include <unistd.h>
#include <signal.h>
#define reconnect_fd_to_display(fd) -1
#define reconnect_to_display() reconnect_fd_to_display(&socket_fd)
#define MDS_VT_VARS_VERSION 0
/**
* This variable should declared by the actual server implementation.
* It must be configured before `main` is invoked.
*
* This tells the server-base how to behave
*/
server_characteristics_t server_characteristics = {
.require_privileges = 1,
/* Required for acquiring a TTY and requesting a VT switch. */
.require_display = 1,
.require_respawn_info = 1,
.sanity_check_argc = 1,
.fork_for_safety = 0,
.danger_is_deadly = 0
};
/**
* Value of the ‘Message ID’ header for the next message
*/
static uint32_t message_id = 1;
/**
* Buffer for received messages
*/
static mds_message_t received;
/**
* Whether the server is connected to the display
*/
static int connected = 1;
/**
* The index of the VT used for the display
*/
static int display_vt;
/**
* The file descriptor the display's TTY is opened on
*/
static int display_tty_fd = -1;
/**
* Whether the display's TTY is in the foreground
*/
static int vt_is_active = 1;
/**
* The stat for the TTY of the display's VT before we toke it
*/
static struct stat old_vt_stat;
/**
* -1 if switching to our VT, 1 if switching to another VT, 0 otherwise
*/
static volatile sig_atomic_t switching_vt = 0;
/**
* The pathname for the file containing VT information
*/
static char vtfile_path[PATH_MAX];
/**
* The file descriptor for the secondary connection to the display
*/
static int secondary_socket_fd;
/**
* Whether the secondary thread has been started
*/
static volatile sig_atomic_t secondary_thread_started = 0;
/**
* The secondary thread
*/
static pthread_t secondary_thread;
/**
* Whether the secondary thread failed
*/
static volatile sig_atomic_t secondary_thread_failed = 0;
/**
* The number of servers currently require non-exclusive mode
*/
static ssize_t nonexclusive_counter = 0;
/**
* This function will be invoked before `initialise_server` (if not re-exec:ing)
* or before `unmarshal_server` (if re-exec:ing)
*
* @return Non-zero on error
*/
int __attribute__((const))
preinitialise_server(void)
{
return 0;
}
/**
* Write persistent data about the VT and TTY to a file
*
* @return Zero on success, -1 on error
*/
static int
write_vt_file(void)
{
char buf[(sizeof(int) + sizeof(struct stat)) / sizeof(char)];
int *intbuf = (int *)buf;
int fd = -1, saved_errno;
*intbuf = display_vt;
*(struct stat *)(buf + sizeof(int) / sizeof(char)) = old_vt_stat;
fail_if (open(vtfile_path, O_WRONLY | O_CREAT, 0644), fd < 0);
fail_if (full_write(fd, buf, sizeof(buf)));
return 0;
fail:
saved_errno = errno;
if (fd >= 0)
xclose(fd);
return errno = saved_errno, -1;
}
/**
* Read persistent data about the VT and TTY from a file
*
* @return Zero on success, -1 on error
*/
static int
read_vt_file(void)
{
char *buf;
size_t len;
int fd;
fail_if (fd = open(vtfile_path, O_RDONLY), fd < 0);
fail_if (buf = full_read(fd, &len), buf == NULL);
if (len != sizeof(int) + sizeof(struct stat)) {
eprint("VT file is of wrong size.");
return errno = 0, -1;
}
display_vt = *(int *)buf;
old_vt_stat = *(struct stat *)(buf + sizeof(int) / sizeof(char));
return 0;
fail:
return -1;
}
/**
* This function should initialise the server,
* and it not invoked after a re-exec.
*
* @return Non-zero on error
*/
int
initialise_server(void)
{
struct vt_mode mode;
char *display_env;
int primary_socket_fd;
int stage = 0;
const char *const message =
"Command: intercept\n"
"Message ID: 0\n"
"Length: 38\n"
"\n"
"Command: get-vt\n"
"Command: configure-vt\n";
const char *const secondary_message =
"Command: intercept\n"
"Message ID: 0\n"
"Priority: -4611686018427387904\n" /* −2⁶² */
"Length: 22\n"
"\n"
"Command: switching-vt\n";
primary_socket_fd = socket_fd;
fail_if (connect_to_display());
secondary_socket_fd = socket_fd;
socket_fd = primary_socket_fd;
display_env = getenv("MDS_DISPLAY");
display_env = display_env ? strchr(display_env, ':') : NULL;
if ((display_env == NULL) || (strlen(display_env) < 2))
goto no_display;
memset(vtfile_path, 0, sizeof(vtfile_path));
xsnprintf(vtfile_path, "%s/%s.vt", MDS_RUNTIME_ROOT_DIRECTORY, display_env + 1);
stage = 1;
if (is_respawn == 0) {
display_vt = select_vt();
fail_if (display_vt < 0);
display_tty_fd = vt_open(display_vt, &old_vt_stat);
fail_if (write_vt_file() < 0);
fail_if (vt_set_active(display_vt) < 0);
} else {
fail_if (read_vt_file() < 0);
vt_is_active = (display_vt == vt_get_active());
fail_if (vt_is_active < 0);
}
fail_if (full_send(secondary_socket_fd, secondary_message, strlen(secondary_message)));
fail_if (full_send(socket_fd, message, strlen(message)));
fail_if (server_initialised() < 0);
fail_if (mds_message_initialise(&received)); stage = 2;
fail_if (xsigaction(SIGRTMIN + 2, received_switch_vt) < 0);
fail_if (xsigaction(SIGRTMIN + 3, received_switch_vt) < 0);
vt_construct_mode(1, SIGRTMIN + 2, SIGRTMIN + 3, &mode);
fail_if (vt_get_set_mode(display_tty_fd, 1, &mode) < 0);
if (vt_set_exclusive(display_tty_fd, 1) < 0)
xperror(*argv);
return 0;
no_display:
eprint("no display has been set, how did this happen.");
return 1;
fail:
xperror(*argv);
if (stage >= 1)
unlink(vtfile_path);
if (display_tty_fd >= 0)
vt_close(display_tty_fd, &old_vt_stat);
if (stage >= 2)
mds_message_destroy(&received);
return 1;
}
/**
* This function will be invoked after `initialise_server` (if not re-exec:ing)
* or after `unmarshal_server` (if re-exec:ing)
*
* @return Non-zero on error
*/
int
postinitialise_server(void)
{
if (connected)
return 0;
if (reconnect_to_display()) {
mds_message_destroy(&received);
fail_if (1);
}
connected = 1;
fail_if ((errno = pthread_create(&secondary_thread, NULL, secondary_loop, NULL)));
return 0;
fail:
return 1;
}
/**
* Calculate the number of bytes that will be stored by `marshal_server`
*
* On failure the program should `abort()` or exit by other means.
* However it should not be possible for this function to fail.
*
* @return The number of bytes that will be stored by `marshal_server`
*/
size_t
marshal_server_size(void)
{
size_t rc = 6 * sizeof(int) + sizeof(uint32_t) + sizeof(ssize_t);
rc += sizeof(struct stat);
rc += PATH_MAX * sizeof(char);
rc += mds_message_marshal_size(&received);
return rc;
}
/**
* Marshal server implementation specific data into a buffer
*
* @param state_buf The buffer for the marshalled data
* @return Non-zero on error
*/
int
marshal_server(char *state_buf)
{
buf_set_next(state_buf, int, MDS_VT_VARS_VERSION);
buf_set_next(state_buf, int, connected);
buf_set_next(state_buf, uint32_t, message_id);
buf_set_next(state_buf, int, display_vt);
buf_set_next(state_buf, int, display_tty_fd);
buf_set_next(state_buf, int, vt_is_active);
buf_set_next(state_buf, struct stat, old_vt_stat);
buf_set_next(state_buf, int, secondary_socket_fd);
buf_set_next(state_buf, ssize_t, nonexclusive_counter);
memcpy(state_buf, vtfile_path, PATH_MAX * sizeof(char));
state_buf += PATH_MAX;
mds_message_marshal(&received, state_buf);
mds_message_destroy(&received);
return 0;
}
/**
* Unmarshal server implementation specific data and update the servers state accordingly
*
* On critical failure the program should `abort()` or exit by other means.
* That is, do not let `reexec_failure_recover` run successfully, if it unrecoverable
* error has occurred or one severe enough that it is better to simply respawn.
*
* @param state_buf The marshalled data that as not been read already
* @return Non-zero on error
*/
int
unmarshal_server(char *state_buf)
{
int r;
/* buf_get_next(state_buf, int, MDS_VT_VARS_VERSION); */
buf_next(state_buf, int, 1);
buf_get_next(state_buf, int, connected);
buf_get_next(state_buf, uint32_t, message_id);
buf_get_next(state_buf, int, display_vt);
buf_get_next(state_buf, int, display_tty_fd);
buf_get_next(state_buf, int, vt_is_active);
buf_get_next(state_buf, struct stat, old_vt_stat);
buf_get_next(state_buf, int, secondary_socket_fd);
buf_get_next(state_buf, ssize_t, nonexclusive_counter);
memcpy(vtfile_path, state_buf, PATH_MAX * sizeof(char));
state_buf += PATH_MAX;
if ((r = mds_message_unmarshal(&received, state_buf))) {
xperror(*argv);
mds_message_destroy(&received);
}
return r;
}
/**
* Attempt to recover from a re-exec failure that has been
* detected after the server successfully updated it execution image
*
* @return Non-zero on error
*/
int __attribute__((const))
reexec_failure_recover(void)
{
return -1;
}
/**
* Perform the server's mission
*
* @return Non-zero on error
*/
int
master_loop(void)
{
int rc = 1, r, leaving;
while (!reexecing && !terminating) {
if (switching_vt) {
leaving = switching_vt == 1;
switching_vt = 0;
r = switch_vt(leaving);
} else if (!(r = mds_message_read(&received, socket_fd))) {
r = handle_message();
}
if (!r) {
continue;
} else if (r == -2) {
eprint("corrupt message received, aborting.");
goto done;
} else if (errno == EINTR) {
continue;
} else {
fail_if (errno != ECONNRESET);
}
eprint("lost primary connection to server.");
mds_message_destroy(&received);
mds_message_initialise(&received);
connected = 0;
fail_if (reconnect_to_display());
connected = 1;
}
rc = 0;
if (vt_set_exclusive(display_tty_fd, 0) < 0)
xperror(*argv);
if (vt_set_graphical(display_tty_fd, 0) < 0)
xperror(*argv);
if (unlink(vtfile_path) < 0)
xperror(*argv);
vt_close(display_tty_fd, &old_vt_stat);
goto done;
fail:
xperror(*argv);
done:
rc |= secondary_thread_failed;
if (rc || !reexecing)
mds_message_destroy(&received);
if ((errno = pthread_join(secondary_thread, NULL)))
xperror(*argv);
return rc;
}
/**
* Wait for confirmation that we may switch virtual terminal
*
* @param data Thread input parameter, will always be `NULL`
* @return Thread return value, will always be `NULL`
*/
void *secondary_loop(void *data)
{
mds_message_t secondary_received;
int r;
secondary_thread_started = 1;
fail_if (mds_message_initialise(&secondary_received) < 0);
while (!reexecing && !terminating) {
if (!(r = mds_message_read(&secondary_received, secondary_socket_fd)))
r = vt_accept_switch(display_tty_fd);
if (!r) {
continue;
} else if (r == -2) {
eprint("corrupt message received, aborting.");
secondary_thread_failed = 1;
goto done;
} else if (errno == EINTR) {
continue;
} else {
fail_if (errno != ECONNRESET);
}
eprint("lost secondary connection to server.");
mds_message_destroy(&secondary_received);
mds_message_initialise(&secondary_received);
fail_if (reconnect_fd_to_display(&secondary_socket_fd) < 0);
}
goto done;
fail:
xperror(*argv);
secondary_thread_failed = 1;
done:
secondary_thread_started = 0;
mds_message_destroy(&secondary_received);
if (!reexecing && !terminating)
pthread_kill(master_thread, SIGTERM);
return NULL;
(void) data;
}
/**
* Perform a VT switch requested by the OS kernel
*
* @param leave_foreground Whether the display is leaving the foreground
* @return Zero on success, -1 on error
*/
int
switch_vt(int leave_foreground)
{
char buf[46 + 22];
sprintf(buf,
"Command: switching-vt\n"
"Message ID: %" PRIu32 "\n"
"Status: %s\n"
"\n",
message_id,
leave_foreground ? "deactivating" : "activating");
message_id = message_id == UINT32_MAX ? 0 : (message_id + 1);
fail_if (full_send(socket_fd, buf, strlen(buf)));
return 0;
fail:
return -1;
}
/**
* Handle the received message
*
* @return Zero on success, -1 on error
*/
int
handle_message(void)
{
/* Fetch message headers. */
const char* recv_client_id = "0:0";
const char* recv_message_id = NULL;
const char* recv_graphical = "neither";
const char* recv_exclusive = "neither";
const char* recv_command = NULL;
size_t i;
#define __get_header(storage, header)\
(startswith(received.headers[i], header))\
storage = received.headers[i] + strlen(header)
for (i = 0; i < received.header_count; i++) {
if __get_header(recv_client_id, "Client ID: ");
else if __get_header(recv_message_id, "Message ID: ");
else if __get_header(recv_graphical, "Graphical: ");
else if __get_header(recv_exclusive, "Exclusive: ");
else if __get_header(recv_command, "Command: ");
}
#undef __get_header
/* Validate headers. */
if (!recv_message_id)
return eprint("received message without ID, ignoring, master server is misbehaving."), 0;
if (strequals(recv_client_id, "0:0"))
return eprint("received information request from an anonymous client, ignoring."), 0;
if (strlen(recv_client_id) > 21)
return eprint("received invalid client ID, ignoring."), 0;
if (strlen(recv_message_id) > 10)
return eprint("received invalid message ID, ignoring."), 0;
/* Take appropriate action. */
if (!recv_command)
return 0; /* How did that get here, no matter, just ignore it? */
if (strequals(recv_command, "get-vt"))
fail_if (handle_get_vt(recv_client_id, recv_message_id));
if (strequals(recv_command, "configure-vt"))
fail_if (handle_configure_vt(recv_client_id, recv_message_id, recv_graphical, recv_exclusive));
return 0; /* How did that get here, no matter, just ignore it? */
fail:
return -1;
}
/**
* Handle a received `Command: get-vt` message
*
* @param client The value of the header `Client ID` in the received message
* @param message The value of the header `Message ID` in the received message
* @return Zero on success, -1 on error
*/
int
handle_get_vt(const char *client, const char *message)
{
char buf[81 + 44 + 3 * sizeof(int)];
int active = vt_get_active();
int r;
sprintf(buf,
"To: %s\n"
"In response to: %s\n"
"Message ID: %" PRIu32 "\n"
"Origin command: get-vt\n"
"VT index: %i\n"
"Active: %s\n"
"\n",
client, message, message_id, display_vt,
active == display_vt ? "yes" : "no");
message_id = message_id == UINT32_MAX ? 0 : (message_id + 1);
r = full_send(socket_fd, buf, strlen(buf));
fail_if ((active < 0) || r);
return 0;
fail:
return -1;
}
/**
* Handle a received `Command: configure-vt` message
*
* @param client The value of the header `Client ID` in the received message
* @param message The value of the header `Message ID` in the received message
* @param graphical The value of the header `Graphical` in the received message
* @param exclusive The value of the header `Exclusive` in the received message
* @return Zero on success, -1 on error
*/
int
handle_configure_vt(const char *client, const char *message, const char *graphical, const char *exclusive)
{
char buf[60 + 41 + 3 * sizeof(int)];
int r = 0, set_nonexclusive;
if (strequals(exclusive, "yes") || strequals(exclusive, "no")) {
/* Switch to exclusive mode when no server has request
non-exclusive mode anymore, and switch to non-exclusive
mode when the number of server that server that has
request non-exclusive switches from zero to one. */
set_nonexclusive = strequals(exclusive, "no");
if (nonexclusive_counter == (ssize_t)!set_nonexclusive)
r |= vt_set_exclusive(display_tty_fd, !set_nonexclusive);
nonexclusive_counter += set_nonexclusive ? 1 : -1;
}
if (strequals(graphical, "yes") || strequals(graphical, "no"))
r |= vt_set_graphical(display_tty_fd, strequals(graphical, "yes"));
sprintf(buf,
"Command: error\n"
"To: %s\n"
"In response to: %s\n"
"Message ID: %" PRIu32 "\n"
"Error: %i\n"
"\n",
client, message, message_id, r);
message_id = message_id == UINT32_MAX ? 0 : (message_id + 1);
fail_if (full_send(socket_fd, buf, strlen(buf)));
return 0;
fail:
return -1;
}
/**
* Send a singal to all threads except the current thread
*
* @param signo The signal
*/
void
signal_all(int signo)
{
pthread_t current_thread = pthread_self();
if (pthread_equal(current_thread, master_thread) == 0)
pthread_kill(master_thread, signo);
else if (secondary_thread_started)
pthread_kill(secondary_thread, signo);
}
/**
* This function is called when the kernel wants
* to switch foreground virtual terminal
*
* @param signo The received signal number
*/
void
received_switch_vt(int signo)
{
SIGHANDLER_START;
int leaving = signo == (SIGRTMIN + 2);
switching_vt = leaving ? 1 : -1;
SIGHANDLER_END;
}
/**
* Get the index of the virtual terminal on which the display should be opened
*
* @return The index of the virtual terminal on which the display should be opened, -1 on error
*/
int
select_vt(void)
{
int rc, r;
const char *xdg_vtnr;
xdg_vtnr = getenv("XDG_VTNR");
if (xdg_vtnr == NULL)
xdg_vtnr = "";
if (*xdg_vtnr) {
/* $XDG_VTNR has been specified, use it to select VT. */
r = strict_atoi(xdg_vtnr, &rc, MIN_NR_CONSOLES, MAX_NR_CONSOLES);
if (r < 0) {
eprint("the environment variable XDG_VTNR contains an invalid value.");
fail_if (errno = 0, 1);
}
} else {
/* $XDG_VTNR has not been specified, select next available VT. */
rc = vt_get_next_available();
if (rc == 0) {
eprint("out of available virtual terminals, I am stymied.");
fail_if (errno = 0, 1);
}
}
return rc;
fail:
return -1;
}
/**
* Get the index of the next available virtual terminal
*
* @return -1 on error, 0 if the terminals are exhausted, otherwise the next terminal
*/
int
vt_get_next_available(void)
{
int next_vt = -1;
fail_if (ioctl(STDIN_FILENO, VT_OPENQRY, &next_vt) < 0);
return ((next_vt < 0) || (MAX_NR_CONSOLES < next_vt)) ? 0 : next_vt;
fail:
return -1;
}
/**
* Get the currently active virtual terminal
*
* @return -1 on error, otherwise the current terminal
*/
int
vt_get_active(void)
{
struct vt_stat state;
fail_if (ioctl(STDIN_FILENO, VT_GETSTATE, &state) < 0);
return state.v_active;
fail:
return -1;
}
/**
* Change currently active virtual terminal and wait for it to complete the switch
*
* @param vt The index of the terminal
* @return Zero on success, -1 on error
*/
int
vt_set_active(int vt)
{
fail_if (ioctl(STDIN_FILENO, VT_ACTIVATE, vt) < 0);
if (ioctl(STDIN_FILENO, VT_WAITACTIVE, vt) < 0)
xperror(*argv);
return 0;
fail:
return -1;
}
/**
* Open a virtual terminal
*
* @param vt The index of the terminal
* @param old_stat Output parameter for the old file stat for the terminal
* @return The file descriptor for the terminal, -1 on error
*/
int
vt_open(int vt, struct stat *restrict old_stat)
{
char vtpath[64]; /* Should be small enough and large enough for any
lunatic alternative to /dev/ttyNNN, if not you
will need to apply a patch (or fix your system.) */
int fd = -1, saved_errno;
sprintf(vtpath, VT_PATH_PATTERN, vt);
fail_if (fd = open(vtpath, O_RDWR), fd < 0);
fail_if ((fstat(fd, old_stat) < 0) || (fchown(fd, getuid(), getgid()) < 0));
return fd;
fail:
saved_errno = errno;
if (fd >= 0)
xclose(fd);
return errno = saved_errno, -1;
}
/**
* Close a virtual terminal
*
* @param vt The index of the terminal
* @param old_stat The old file stat for the terminal
*/
void
vt_close(int fd, struct stat *restrict old_stat)
{
if (fchown(fd, old_stat->st_uid, old_stat->st_gid) < 0) {
xperror(*argv);
eprint("while resetting TTY ownership.");
}
xclose(fd);
}
/**
* Construct a virtual terminal mode that can be used in `vt_get_set_mode`
*
* @param vt_switch_control Whether we want to be able to block and delay VT switches
* @param vt_leave_signal The signal that should be send to us we a process is trying
* to switch terminal to another terminal
* @param vt_enter_signal The signal that should be send to us we a process is trying
* to switch terminal to our terminal
* @param mode Output parameter
*/
void
vt_construct_mode(int vt_switch_control, int vt_leave_signal,
int vt_enter_signal, struct vt_mode *restrict mode)
{
mode->mode = vt_switch_control ? VT_PROCESS : VT_AUTO;
mode->waitv = 0;
mode->relsig = (short int)vt_leave_signal;
mode->acqsig = (short int)vt_enter_signal;
}
/**
* This function is called when a signal that
* signals that the system to dump state information
* and statistics has been received
*
* @param signo The signal that has been received
*/
void
received_info(int signo)
{
SIGHANDLER_START;
(void) signo;
iprintf("next message ID: %" PRIu32, message_id);
iprintf("connected: %s", connected ? "yes" : "no");
iprintf("VT of the display: %i", display_vt);
iprintf("TTY FD of the display: %i", display_tty_fd);
iprintf("TTY in foreground: %s", vt_is_active ? "yes" : "no");
iprintf("old VT stat: mode: %lo", (long)(old_vt_stat.st_mode));
iprintf("old VT stat: uid: %li", (long)(old_vt_stat.st_uid));
iprintf("old VT stat: gid: %li", (long)(old_vt_stat.st_gid));
iprintf("switching VT: %s", switching_vt ? "yes" : "no");
iprintf("VT-file pathname: %s", vtfile_path);
iprintf("secondary socket FD: %i", secondary_socket_fd);
iprintf("secondary thread started: %s", secondary_thread_started ? "yes" : "no");
iprintf("secondary thread failed: %s", secondary_thread_failed ? "yes" : "no");
iprintf("non-exclusive counter: %zi", nonexclusive_counter);
SIGHANDLER_END;
}
