/*
  * safe_finger - finger client wrapper that protects against nasty stuff
  * from finger servers. Use this program for automatic reverse finger
  * probes, not the raw finger command.
  *
  * Build with: cc -o safe_finger safe_finger.c
  *
  * The problem: some programs may react to stuff in the first column. Other
  * programs may get upset by thrash anywhere on a line. File systems may
  * fill up as the finger server keeps sending data. Text editors may bomb
  * out on extremely long lines. The finger server may take forever because
  * it is somehow wedged. The code below takes care of all this badness.
  *
  * Author: Wietse Venema, Eindhoven University of Technology, The Netherlands.
  */

/* System libraries */

#include <sys/types.h>
#include <sys/stat.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <pwd.h>

extern void exit();

/* Local stuff */

char    path[] = "PATH=/bin:/usr/bin:/usr/ucb:/usr/bsd:/etc:/usr/etc:/usr/sbin";

#define TIME_LIMIT      60              /* Do not keep listinging forever */
#define INPUT_LENGTH    100000          /* Do not keep listinging forever */
#define LINE_LENGTH     128             /* Editors can choke on long lines */
#define FINGER_PROGRAM  "finger"        /* Most, if not all, UNIX systems */
#define UNPRIV_NAME     "nobody"        /* Preferred privilege level */
#define UNPRIV_UGID     32767           /* Default uid and gid */

void    perror_exit(char *text) __NORETURN;
int     finger_pid;

void    cleanup(sig)
int     sig;
{
    kill(finger_pid, SIGKILL);
    exit(0);
}

int
main(argc, argv)
int     argc;
char  **argv;
{
    int     c;
    int     line_length = 0;
    int     finger_status;
    int     wait_pid;
    int     input_count = 0;
    struct passwd *pwd;

    /*
     * First of all, let's don't run with superuser privileges.
     */
    if (getuid() == 0 || geteuid() == 0) {
        if ((pwd = getpwnam(UNPRIV_NAME)) && pwd->pw_uid > 0) {
            setgid(pwd->pw_gid);
            setuid(pwd->pw_uid);
        } else {
            setgid(UNPRIV_UGID);
            setuid(UNPRIV_UGID);
        }
    }

    /*
     * Redirect our standard input through the raw finger command.
     */
    if (putenv(path)) {
        fprintf(stderr, "%s: putenv: out of memory", argv[0]);
        exit(1);
    }
    argv[0] = FINGER_PROGRAM;
    finger_pid = pipe_stdin(argv);

    /*
     * Don't wait forever (Peter Wemm <peter@gecko.DIALix.oz.au>).
     */
    signal(SIGALRM, cleanup);
    (void) alarm(TIME_LIMIT);

    /*
     * Main filter loop.
     */
    while ((c = getchar()) != EOF) {
        if (input_count++ >= INPUT_LENGTH) {    /* don't listen forever */
            fclose(stdin);
            printf("\n\n Input truncated to %d bytes...\n", input_count - 1);
            break;
        }
        if (c == '\n') {                        /* good: end of line */
            putchar(c);
            line_length = 0;
        } else {
            if (line_length >= LINE_LENGTH) {   /* force end of line */
                printf("\\\n");
                line_length = 0;
            }
            if (line_length == 0) {             /* protect left margin */
                putchar(' ');
                line_length++;
            }
            if (isascii(c) && (isprint(c) || isspace(c))) {     /* text */
                if (c == '\\') {
                    putchar(c);
                    line_length++;
                }
                putchar(c);
                line_length++;
            } else {                            /* quote all other thash */
                printf("\\%03o", c & 0377);
                line_length += 4;
            }
        }
    }

    /*
     * Wait until the finger child process has terminated and account for its
     * exit status. Which will always be zero on most systems.
     */
    while ((wait_pid = wait(&finger_status)) != -1 && wait_pid != finger_pid)
         /* void */ ;
    return (wait_pid != finger_pid || finger_status != 0);
}

/* perror_exit - report system error text and terminate */

void
perror_exit(char *text)
{
    perror(text);
    exit(1);
}

/* pipe_stdin - pipe stdin through program (from my ANSI to OLD C converter) */

int     pipe_stdin(argv)
char  **argv;
{
    int     pipefds[2];
    int     pid;
    int     i;
    struct stat st;

    /*
     * The code that sets up the pipe requires that file descriptors 0,1,2
     * are already open. All kinds of mysterious things will happen if that
     * is not the case. The following loops makes sure that descriptors 0,1,2
     * are set up properly.
     */

    for (i = 0; i < 3; i++) {
        if (fstat(i, &st) == -1 && open("/dev/null", 2) != i)
            perror_exit("open /dev/null");
    }

    /*
     * Set up the pipe that interposes the command into our standard input
     * stream.
     */

    if (pipe(pipefds))
        perror_exit("pipe");

    switch (pid = fork()) {
    case -1:                                    /* error */
        perror_exit("fork");
        /* NOTREACHED */
    case 0:                                     /* child */
        (void) close(pipefds[0]);               /* close reading end */
        (void) close(1);                        /* connect stdout to pipe */
        if (dup(pipefds[1]) != 1)
            perror_exit("dup");
        (void) close(pipefds[1]);               /* close redundant fd */
        (void) execvp(argv[0], argv);
        perror_exit(argv[0]);
        /* NOTREACHED */
    default:                                    /* parent */
        (void) close(pipefds[1]);               /* close writing end */
        (void) close(0);                        /* connect stdin to pipe */
        if (dup(pipefds[0]) != 0)
            perror_exit("dup");
        (void) close(pipefds[0]);               /* close redundant fd */
        return (pid);
    }
}