pty.c

大名鼎鼎的远程登录软件putty的Symbian版源码

/*
 * Pseudo-tty backend for pterm.
 * 
 * Unlike the other backends, data for this one is not neatly
 * encapsulated into a data structure, because it wouldn't make
 * sense to do so - the utmp stuff has to be done before a backend
 * is initialised, and starting a second pterm from the same
 * process would therefore be infeasible because privileges would
 * already have been dropped. Hence, I haven't bothered to keep the
 * data dynamically allocated: instead, the backend handle is just
 * a null pointer and ignored everywhere.
 */

#define _XOPEN_SOURCE
#define _XOPEN_SOURCE_EXTENDED
#define _GNU_SOURCE
#include <features.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.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/wait.h>
#include <sys/ioctl.h>
#include <errno.h>

#include "putty.h"

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

#ifndef UTMP_FILE
#define UTMP_FILE "/var/run/utmp"
#endif
#ifndef WTMP_FILE
#define WTMP_FILE "/var/log/wtmp"
#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

static Config pty_cfg;
static int pty_master_fd;
static void *pty_frontend;
static char pty_name[FILENAME_MAX];
static int pty_signal_pipe[2];
static int pty_stamped_utmp = 0;
static int pty_child_pid;
static int pty_utmp_helper_pid, pty_utmp_helper_pipe;
static int pty_term_width, pty_term_height;
static int pty_child_dead, pty_finished;
static int pty_exit_code;
#ifndef OMIT_UTMP
static struct utmp utmp_entry;
#endif
char **pty_argv;
int use_pty_argv = TRUE;

static void pty_close(void);

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

    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 utmp).ut_time
     * is not essentially time_t (e.g. Linux amd64). Hence the temporary. */
    time(&uttime);
    utmp_entry.ut_time = uttime; /* may truncate */

#if defined HAVE_PUTUTLINE
    utmpname(UTMP_FILE);
    setutent();
    pututline(&utmp_entry);
    endutent();
#endif

    if ((wtmp = fopen(WTMP_FILE, "a")) != NULL) {
	fwrite(&utmp_entry, 1, sizeof(utmp_entry), wtmp);
	fclose(wtmp);
    }

#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;

#endif
}

static void cleanup_utmp(void)
{
#ifndef OMIT_UTMP
    FILE *wtmp;
    time_t uttime;

    if (!pty_stamped_utmp)
	return;

    utmp_entry.ut_type = DEAD_PROCESS;
    memset(utmp_entry.ut_user, 0, lenof(utmp_entry.ut_user));
    time(&uttime);
    utmp_entry.ut_time = uttime;

    if ((wtmp = fopen(WTMP_FILE, "a")) != NULL) {
	fwrite(&utmp_entry, 1, sizeof(utmp_entry), wtmp);
	fclose(wtmp);
    }

    memset(utmp_entry.ut_line, 0, lenof(utmp_entry.ut_line));
    utmp_entry.ut_time = 0;

#if defined HAVE_PUTUTLINE
    utmpname(UTMP_FILE);
    setutent();
    pututline(&utmp_entry);
    endutent();
#endif

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

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

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

static void pty_open_master(void)
{
#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)
		    goto got_one;
		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:
    strcpy(pty_name, master_name);
    pty_name[5] = 't';		       /* /dev/ptyXX -> /dev/ttyXX */

    /* 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);
    }

    pty_name[FILENAME_MAX-1] = '\0';
    strncpy(pty_name, ptsname(pty_master_fd), FILENAME_MAX-1);
#endif
}

/*
 * 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)
{
    pid_t pid;
    int pipefd[2];

    /* set the child signal handler straight away; it needs to be set
     * before we ever fork. */
    putty_signal(SIGCHLD, sigchld_handler);
    pty_master_fd = -1;

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

#ifndef OMIT_UTMP
    /*
     * Fork off the utmp helper.
     */
    if (pipe(pipefd) < 0) {
	perror("pterm: pipe");
	exit(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. */
    {
	int gid = getgid(), uid = getuid();
#ifndef HAVE_NO_SETRESUID
	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_select_result(int fd, int event)
{
    char buf[4096];
    int ret;
    int finished = FALSE;

    if (fd == pty_master_fd && event == 1) {

	ret = read(pty_master_fd, buf, sizeof(buf));

	/*
	 * Clean termination condition is that either ret == 0, or ret
	 * < 0 and errno == EIO. Not sure why the latter, but it seems
	 * to happen. Boo.
	 */
	if (ret == 0 || (ret < 0 && errno == EIO)) {
	    /*
	     * We assume a clean exit if the pty has closed but the
	     * actual child process hasn't. The only way I can
	     * imagine this happening is if it detaches itself from
	     * the pty and goes daemonic - in which case the
	     * expected usage model would precisely _not_ be for
	     * the pterm window to hang around!
	     */