uxpty.c

putty

/*
 * Pseudo-tty backend for pterm.
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <assert.h>
#include <fcntl.h>
#include <termios.h>
#include <grp.h>
#include <utmp.h>
#include <pwd.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <sys/ioctl.h>
#include <errno.h>

#include "putty.h"
#include "tree234.h"

#ifndef OMIT_UTMP
#include <utmpx.h>
#endif

#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif

/* updwtmpx() needs the name of the wtmp file.  Try to find it. */
#ifndef WTMPX_FILE
#ifdef _PATH_WTMPX
#define WTMPX_FILE _PATH_WTMPX
#else
#define WTMPX_FILE "/var/log/wtmpx"
#endif
#endif

#ifndef LASTLOG_FILE
#ifdef _PATH_LASTLOG
#define LASTLOG_FILE _PATH_LASTLOG
#else
#define LASTLOG_FILE "/var/log/lastlog"
#endif
#endif

/*
 * Set up a default for vaguely sane systems. The idea is that if
 * OMIT_UTMP is not defined, then at least one of the symbols which
 * enable particular forms of utmp processing should be, if only so
 * that a link error can warn you that you should have defined
 * OMIT_UTMP if you didn't want any. Currently HAVE_PUTUTLINE is
 * the only such symbol.
 */
#ifndef OMIT_UTMP
#if !defined HAVE_PUTUTLINE
#define HAVE_PUTUTLINE
#endif
#endif

typedef struct pty_tag *Pty;

/*
 * The pty_signal_pipe, along with the SIGCHLD handler, must be
 * process-global rather than session-specific.
 */
static int pty_signal_pipe[2] = { -1, -1 };   /* obviously bogus initial val */

struct pty_tag {
    Config cfg;
    int master_fd, slave_fd;
    void *frontend;
    char name[FILENAME_MAX];
    int child_pid;
    int term_width, term_height;
    int child_dead, finished;
    int exit_code;
    bufchain output_data;
};

/*
 * We store our pty backends in a tree sorted by master fd, so that
 * when we get an uxsel notification we know which backend instance
 * is the owner of the pty that caused it.
 */
static int pty_compare_by_fd(void *av, void *bv)
{
    Pty a = (Pty)av;
    Pty b = (Pty)bv;

    if (a->master_fd < b->master_fd)
	return -1;
    else if (a->master_fd > b->master_fd)
	return +1;
    return 0;
}

static int pty_find_by_fd(void *av, void *bv)
{
    int a = *(int *)av;
    Pty b = (Pty)bv;

    if (a < b->master_fd)
	return -1;
    else if (a > b->master_fd)
	return +1;
    return 0;
}

static tree234 *ptys_by_fd = NULL;

/*
 * We also have a tree sorted by child pid, so that when we wait()
 * in response to the signal we know which backend instance is the
 * owner of the process that caused the signal.
 */
static int pty_compare_by_pid(void *av, void *bv)
{
    Pty a = (Pty)av;
    Pty b = (Pty)bv;

    if (a->child_pid < b->child_pid)
	return -1;
    else if (a->child_pid > b->child_pid)
	return +1;
    return 0;
}

static int pty_find_by_pid(void *av, void *bv)
{
    int a = *(int *)av;
    Pty b = (Pty)bv;

    if (a < b->child_pid)
	return -1;
    else if (a > b->child_pid)
	return +1;
    return 0;
}

static tree234 *ptys_by_pid = NULL;

/*
 * If we are using pty_pre_init(), it will need to have already
 * allocated a pty structure, which we must then return from
 * pty_init() rather than allocating a new one. Here we store that
 * structure between allocation and use.
 * 
 * Note that although most of this module is entirely capable of
 * handling multiple ptys in a single process, pty_pre_init() is
 * fundamentally _dependent_ on there being at most one pty per
 * process, so the normal static-data constraints don't apply.
 * 
 * Likewise, since utmp is only used via pty_pre_init, it too must
 * be single-instance, so we can declare utmp-related variables
 * here.
 */
static Pty single_pty = NULL;

#ifndef OMIT_UTMP
static int pty_utmp_helper_pid, pty_utmp_helper_pipe;
static int pty_stamped_utmp;
static struct utmpx utmp_entry;
#endif

/*
 * pty_argv is a grievous hack to allow a proper argv to be passed
 * through from the Unix command line. Again, it doesn't really
 * make sense outside a one-pty-per-process setup.
 */
char **pty_argv;

static void pty_close(Pty pty);
static void pty_try_write(Pty pty);

#ifndef OMIT_UTMP
static void setup_utmp(char *ttyname, char *location)
{
#ifdef HAVE_LASTLOG
    struct lastlog lastlog_entry;
    FILE *lastlog;
#endif
    struct passwd *pw;
    struct timeval tv;

    pw = getpwuid(getuid());
    memset(&utmp_entry, 0, sizeof(utmp_entry));
    utmp_entry.ut_type = USER_PROCESS;
    utmp_entry.ut_pid = getpid();
    strncpy(utmp_entry.ut_line, ttyname+5, lenof(utmp_entry.ut_line));
    strncpy(utmp_entry.ut_id, ttyname+8, lenof(utmp_entry.ut_id));
    strncpy(utmp_entry.ut_user, pw->pw_name, lenof(utmp_entry.ut_user));
    strncpy(utmp_entry.ut_host, location, lenof(utmp_entry.ut_host));
    /*
     * Apparently there are some architectures where (struct
     * utmpx).ut_tv is not essentially struct timeval (e.g. Linux
     * amd64). Hence the temporary.
     */
    gettimeofday(&tv, NULL);
    utmp_entry.ut_tv.tv_sec = tv.tv_sec;
    utmp_entry.ut_tv.tv_usec = tv.tv_usec;

    setutxent();
    pututxline(&utmp_entry);
    endutxent();

    updwtmpx(WTMPX_FILE, &utmp_entry);

#ifdef HAVE_LASTLOG
    memset(&lastlog_entry, 0, sizeof(lastlog_entry));
    strncpy(lastlog_entry.ll_line, ttyname+5, lenof(lastlog_entry.ll_line));
    strncpy(lastlog_entry.ll_host, location, lenof(lastlog_entry.ll_host));
    time(&lastlog_entry.ll_time);
    if ((lastlog = fopen(LASTLOG_FILE, "r+")) != NULL) {
	fseek(lastlog, sizeof(lastlog_entry) * getuid(), SEEK_SET);
	fwrite(&lastlog_entry, 1, sizeof(lastlog_entry), lastlog);
	fclose(lastlog);
    }
#endif

    pty_stamped_utmp = 1;

}

static void cleanup_utmp(void)
{
    struct timeval tv;

    if (!pty_stamped_utmp)
	return;

    utmp_entry.ut_type = DEAD_PROCESS;
    memset(utmp_entry.ut_user, 0, lenof(utmp_entry.ut_user));
    gettimeofday(&tv, NULL);
    utmp_entry.ut_tv.tv_sec = tv.tv_sec;
    utmp_entry.ut_tv.tv_usec = tv.tv_usec;

    updwtmpx(WTMPX_FILE, &utmp_entry);

    memset(utmp_entry.ut_line, 0, lenof(utmp_entry.ut_line));
    utmp_entry.ut_tv.tv_sec = 0;
    utmp_entry.ut_tv.tv_usec = 0;

    setutxent();
    pututxline(&utmp_entry);
    endutxent();

    pty_stamped_utmp = 0;	       /* ensure we never double-cleanup */
}
#endif

static void sigchld_handler(int signum)
{
    write(pty_signal_pipe[1], "x", 1);
}

#ifndef OMIT_UTMP
static void fatal_sig_handler(int signum)
{
    putty_signal(signum, SIG_DFL);
    cleanup_utmp();
    setuid(getuid());
    raise(signum);
}
#endif

static int pty_open_slave(Pty pty)
{
    if (pty->slave_fd < 0) {
	pty->slave_fd = open(pty->name, O_RDWR);
        cloexec(pty->slave_fd);
    }

    return pty->slave_fd;
}

static void pty_open_master(Pty pty)
{
#ifdef BSD_PTYS
    const char chars1[] = "pqrstuvwxyz";
    const char chars2[] = "0123456789abcdef";
    const char *p1, *p2;
    char master_name[20];
    struct group *gp;

    for (p1 = chars1; *p1; p1++)
	for (p2 = chars2; *p2; p2++) {
	    sprintf(master_name, "/dev/pty%c%c", *p1, *p2);
	    pty->master_fd = open(master_name, O_RDWR);
	    if (pty->master_fd >= 0) {
		if (geteuid() == 0 ||
		    access(master_name, R_OK | W_OK) == 0) {
		    /*
		     * We must also check at this point that we are
		     * able to open the slave side of the pty. We
		     * wouldn't want to allocate the wrong master,
		     * get all the way down to forking, and _then_
		     * find we're unable to open the slave.
		     */
		    strcpy(pty->name, master_name);
		    pty->name[5] = 't'; /* /dev/ptyXX -> /dev/ttyXX */

                    cloexec(pty->master_fd);

		    if (pty_open_slave(pty) >= 0 &&
			access(pty->name, R_OK | W_OK) == 0)
			goto got_one;
		    if (pty->slave_fd > 0)
			close(pty->slave_fd);
		    pty->slave_fd = -1;
		}
		close(pty->master_fd);
	    }
	}

    /* If we get here, we couldn't get a tty at all. */
    fprintf(stderr, "pterm: unable to open a pseudo-terminal device\n");
    exit(1);

    got_one:

    /* We need to chown/chmod the /dev/ttyXX device. */
    gp = getgrnam("tty");
    chown(pty->name, getuid(), gp ? gp->gr_gid : -1);
    chmod(pty->name, 0600);
#else
    pty->master_fd = open("/dev/ptmx", O_RDWR);

    if (pty->master_fd < 0) {
	perror("/dev/ptmx: open");
	exit(1);
    }

    if (grantpt(pty->master_fd) < 0) {
	perror("grantpt");
	exit(1);
    }
    
    if (unlockpt(pty->master_fd) < 0) {
	perror("unlockpt");
	exit(1);
    }

    cloexec(pty->master_fd);

    pty->name[FILENAME_MAX-1] = '\0';
    strncpy(pty->name, ptsname(pty->master_fd), FILENAME_MAX-1);
#endif

    {
        /*
         * Set the pty master into non-blocking mode.
         */
        int i = 1;
        ioctl(pty->master_fd, FIONBIO, &i);
    }

    if (!ptys_by_fd)
	ptys_by_fd = newtree234(pty_compare_by_fd);
    add234(ptys_by_fd, pty);
}

/*
 * Pre-initialisation. This is here to get around the fact that GTK
 * doesn't like being run in setuid/setgid programs (probably
 * sensibly). So before we initialise GTK - and therefore before we
 * even process the command line - we check to see if we're running
 * set[ug]id. If so, we open our pty master _now_, chown it as
 * necessary, and drop privileges. We can always close it again
 * later. If we're potentially going to be doing utmp as well, we
 * also fork off a utmp helper process and communicate with it by
 * means of a pipe; the utmp helper will keep privileges in order
 * to clean up utmp when we exit (i.e. when its end of our pipe
 * closes).
 */
void pty_pre_init(void)
{
    Pty pty;

#ifndef OMIT_UTMP
    pid_t pid;
    int pipefd[2];
#endif

    pty = single_pty = snew(struct pty_tag);
    bufchain_init(&pty->output_data);

    /* set the child signal handler straight away; it needs to be set
     * before we ever fork. */
    putty_signal(SIGCHLD, sigchld_handler);
    pty->master_fd = pty->slave_fd = -1;
#ifndef OMIT_UTMP
    pty_stamped_utmp = FALSE;
#endif

    if (geteuid() != getuid() || getegid() != getgid()) {
	pty_open_master(pty);
    }

#ifndef OMIT_UTMP
    /*
     * Fork off the utmp helper.
     */
    if (pipe(pipefd) < 0) {
	perror("pterm: pipe");
	exit(1);
    }
    cloexec(pipefd[0]);
    cloexec(pipefd[1]);
    pid = fork();
    if (pid < 0) {
	perror("pterm: fork");
	exit(1);
    } else if (pid == 0) {
	char display[128], buffer[128];
	int dlen, ret;

	close(pipefd[1]);
	/*
	 * Now sit here until we receive a display name from the
	 * other end of the pipe, and then stamp utmp. Unstamp utmp
	 * again, and exit, when the pipe closes.
	 */

	dlen = 0;
	while (1) {
	    
	    ret = read(pipefd[0], buffer, lenof(buffer));
	    if (ret <= 0) {
		cleanup_utmp();
		_exit(0);
	    } else if (!pty_stamped_utmp) {
		if (dlen < lenof(display))
		    memcpy(display+dlen, buffer,
			   min(ret, lenof(display)-dlen));
		if (buffer[ret-1] == '\0') {
		    /*
		     * Now we have a display name. NUL-terminate
		     * it, and stamp utmp.
		     */
		    display[lenof(display)-1] = '\0';
		    /*
		     * Trap as many fatal signals as we can in the
		     * hope of having the best possible chance to
		     * clean up utmp before termination. We are
		     * unfortunately unprotected against SIGKILL,
		     * but that's life.
		     */
		    putty_signal(SIGHUP, fatal_sig_handler);
		    putty_signal(SIGINT, fatal_sig_handler);
		    putty_signal(SIGQUIT, fatal_sig_handler);
		    putty_signal(SIGILL, fatal_sig_handler);
		    putty_signal(SIGABRT, fatal_sig_handler);
		    putty_signal(SIGFPE, fatal_sig_handler);
		    putty_signal(SIGPIPE, fatal_sig_handler);
		    putty_signal(SIGALRM, fatal_sig_handler);
		    putty_signal(SIGTERM, fatal_sig_handler);
		    putty_signal(SIGSEGV, fatal_sig_handler);
		    putty_signal(SIGUSR1, fatal_sig_handler);
		    putty_signal(SIGUSR2, fatal_sig_handler);
#ifdef SIGBUS
		    putty_signal(SIGBUS, fatal_sig_handler);
#endif
#ifdef SIGPOLL
		    putty_signal(SIGPOLL, fatal_sig_handler);
#endif
#ifdef SIGPROF
		    putty_signal(SIGPROF, fatal_sig_handler);
#endif
#ifdef SIGSYS
		    putty_signal(SIGSYS, fatal_sig_handler);
#endif
#ifdef SIGTRAP
		    putty_signal(SIGTRAP, fatal_sig_handler);
#endif
#ifdef SIGVTALRM
		    putty_signal(SIGVTALRM, fatal_sig_handler);
#endif
#ifdef SIGXCPU
		    putty_signal(SIGXCPU, fatal_sig_handler);
#endif
#ifdef SIGXFSZ
		    putty_signal(SIGXFSZ, fatal_sig_handler);
#endif
#ifdef SIGIO
		    putty_signal(SIGIO, fatal_sig_handler);
#endif
		    setup_utmp(pty->name, display);
		}
	    }
	}
    } else {
	close(pipefd[0]);
	pty_utmp_helper_pid = pid;
	pty_utmp_helper_pipe = pipefd[1];
    }
#endif

    /* Drop privs. */
    {
#ifndef HAVE_NO_SETRESUID
	int gid = getgid(), uid = getuid();
	int setresgid(gid_t, gid_t, gid_t);
	int setresuid(uid_t, uid_t, uid_t);
	setresgid(gid, gid, gid);
	setresuid(uid, uid, uid);
#else
	setgid(getgid());
	setuid(getuid());
#endif
    }
}

int pty_real_select_result(Pty pty, int event, int status)
{
    char buf[4096];
    int ret;
    int finished = FALSE;

    if (event < 0) {
	/*
	 * We've been called because our child process did
	 * something. `status' tells us what.
	 */
	if ((WIFEXITED(status) || WIFSIGNALED(status))) {
	    /*
	     * The primary child process died. We could keep
	     * the terminal open for remaining subprocesses to
	     * output to, but conventional wisdom seems to feel
	     * that that's the Wrong Thing for an xterm-alike,
	     * so we bail out now (though we don't necessarily
	     * _close_ the window, depending on the state of
	     * Close On Exit). This would be easy enough to
	     * change or make configurable if necessary.
	     */
	    pty->exit_code = status;