/*
* Receive wall messages and pass them to a notification program via stdin.
*
* Copyright (C) 2014 Simon Ruderich
*
* 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 .
*/
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#ifdef USE_UTEMPTER
# include
#endif
#ifdef USE_UTMPX
# include
#endif
static void sig_handler(int signal) {
(void)signal;
}
static void setup_signals(void) {
struct sigaction action;
memset(&action, 0, sizeof(action));
sigemptyset(&action.sa_mask);
action.sa_handler = sig_handler;
/* Handle all important signals which might be sent to us so we break out
* of the read()-loop below and can perform our cleanup. */
sigaction(SIGHUP, &action, NULL);
sigaction(SIGINT, &action, NULL);
sigaction(SIGQUIT, &action, NULL);
sigaction(SIGUSR1, &action, NULL);
sigaction(SIGUSR2, &action, NULL);
/* Collect zombies automatically without having to call waitpid(2). */
signal(SIGCHLD, SIG_IGN);
}
static int open_tty(void) {
int ptm;
const char *name;
ptm = posix_openpt(O_RDWR);
if (ptm < 0) {
return -1;
}
if (grantpt(ptm) != 0) {
return -1;
}
/* Prevent write access for other users so they can't use wall to send
* messages to this program. */
name = ptsname(ptm);
if (!name) {
return -1;
}
if (chmod(name, S_IRUSR | S_IWUSR) != 0) {
return -1;
}
if (unlockpt(ptm) != 0) {
return -1;
}
return ptm;
}
#ifdef USE_UTMPX
static const char *skip_prefix(const char *string, const char *prefix) {
size_t length = strlen(prefix);
if (!strncmp(string, prefix, length)) {
return string + length;
} else {
return string;
}
}
static int set_utmpx(short type, int ptm) {
struct utmpx entry;
const char *tty, *user, *id, *line;
struct timeval now;
user = getpwuid(getuid())->pw_name;
gettimeofday(&now, NULL);
tty = ptsname(ptm);
if (!tty) {
return 0;
}
id = skip_prefix(tty, "/dev/pts/");
line = skip_prefix(tty, "/dev/");
/* Create utmp entry for the given terminal. */
memset(&entry, 0, sizeof(entry));
snprintf(entry.ut_user, sizeof(entry.ut_user), "%s", user);
snprintf(entry.ut_id, sizeof(entry.ut_id), "%s", id);
snprintf(entry.ut_line, sizeof(entry.ut_line), "%s", line);
entry.ut_pid = getpid();
entry.ut_type = type;
entry.ut_tv.tv_sec = now.tv_sec;
entry.ut_tv.tv_usec = now.tv_usec;
/* Write the entry to the utmp file. */
setutxent();
if (!pututxline(&entry)) {
return 0;
}
endutxent();
return 1;
}
#endif
static int login(int ptm) {
#if defined(USE_UTEMPTER)
return utempter_add_record(ptm, NULL);
#elif defined(USE_UTMPX)
return set_utmpx(USER_PROCESS, ptm);
#else
# error "neither USE_UTEMPTER nor USE_UTMPX defined"
#endif
}
static int logout(int ptm) {
#if defined(USE_UTEMPTER)
return utempter_remove_record(ptm);
#elif defined(USE_UTMPX)
return set_utmpx(DEAD_PROCESS, ptm);
#else
# error "neither USE_UTEMPTER nor USE_UTMPX defined"
#endif
}
static void pass_buffer_to_program(const char *buffer, size_t length, char **argv) {
int fds[2];
FILE *fh;
pid_t pid;
/* Skip argv[0]. */
argv++;
if (pipe(fds) != 0) {
perror("pipe");
return;
}
fh = fdopen(fds[1] /* write side */, "w");
if (!fh) {
perror("fdopen");
close(fds[0]);
close(fds[1]);
return;
}
pid = fork();
if (pid < 0) {
perror("fork");
goto out;
} else if (pid == 0) {
/* child */
close(fds[1]); /* write side */
/* Pass read side as stdin to the program. */
if (dup2(fds[0], STDIN_FILENO) < 0) {
perror("dup2");
exit(EXIT_FAILURE);
}
close(fds[0]);
execvp(argv[0], argv);
perror("execvp");
exit(EXIT_FAILURE);
}
/* father */
if (fwrite(buffer, 1, length, fh) != length) {
perror("fwrite");
/* continue to perform cleanup */
}
out:
close(fds[0]); /* read side */
fclose(fh);
}
static void handle_wall(int fd, char **argv) {
char buffer[4096];
ssize_t r;
while ((r = read(fd, buffer, sizeof(buffer))) > 0) {
assert(SSIZE_MAX <= SIZE_MAX);
pass_buffer_to_program(buffer, (size_t)r, argv);
}
}
int main(int argc, char **argv) {
int ptm, pts;
char *name;
if (argc < 2) {
fprintf(stderr, "usage: %s \n", argv[0]);
exit(EXIT_FAILURE);
}
ptm = open_tty();
if (ptm < 0) {
perror("open_tty");
exit(EXIT_FAILURE);
}
name = ptsname(ptm);
if (!name) {
perror("ptsname");
exit(EXIT_FAILURE);
}
#ifdef DEBUG
printf("%s\n", name);
#endif
/* We need to open the slave or reading from the master yields EOF after
* the first wall write to it. */
pts = open(name, O_RDWR);
if (pts < 0) {
perror(name);
exit(EXIT_FAILURE);
}
/* Cleanup on signals. Necessary before login(). */
setup_signals();
if (!login(ptm)) {
perror("login");
exit(EXIT_FAILURE);
}
/* Main loop. Handle all wall messages sent to our PTY. */
handle_wall(ptm, argv);
if (!logout(ptm)) {
perror("logout");
exit(EXIT_FAILURE);
}
close(ptm);
close(pts);
return EXIT_SUCCESS;
}