Source Code 1992 March/Source_Code_CD-ROM_Walnut_Creek_March_1992.iso/usenet/altsrcs/3/3437

Internet Message Format | 1991-06-04 | 4.4 KB

From: [e-mail] (John F Haugh II)
Newsgroups: alt.security,alt.sources
Subject: Re: Sun security problem with floppies.
Message-ID: <[e-mail]>
Date: 2 Jun 91 19:34:12 GMT

In article <[e-mail]> [e-mail] (Jyrki Kuoppala) writes:
>I'd suppose that floppies on a Sun are used mostly to transfer data to
>some other kinds of computers, writing some personal files with tar,
>using MS-LOSS tools or something like that, not mounting them.  Making
>the floppy device unreadable would make it useless for this purpose.
>
>Suggested fix: don't mount the floppy in the first place.

Better Suggested Fix:

Write a little utility which will change the ownership of the floppy
disk from some standard UID that you make up to own the device to the
real UID of the invoker.  Something like this -
--
#if    0
cc -o checkin -DHAVE_FUSER checkinout.c
touch /etc/checkinout
cp checkin /usr/local/bin
ln /usr/local/bin/checkin /usr/local/bin/checkout
chown root /usr/local/bin/checkin
chmod 400 /etc/checkinout
chmod 4711 /usr/local/bin/checkin
exit 0
#endif

/*
 * checkinout.c - manage a sharable device
 *
 *    You must define the HAVE_FCHOWN macro on the compile command
 *    line if you have the fchown() system call.
 *    Otherwise don't bother using this thing because it can let
 *    anyone change the ownership of any file (more or less ...)
 *    It is only safe without HAVE_FCHOWN if you have no writable
 *    directories on the root partition (which should be the only
 *    place with files owned by UNUSED_NAME) and if your system
 *    does not have symbolic links.
 *
 *    You should define the HAVE_FUSER macro if you have the fuser
 *    command.  It will be used to clean the device before giving
 *    it to you.
 *
 *    To compile and install this source code, feed to /bin/sh
 *    as root.
 */

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

#define    UNUSED_NAME    "share"
#define    SHARE_FILES    "/etc/checkinout"

usage ()
{
    fprintf (stderr, "usage:\tcheckin <device>\n\tcheckout <device>\n");
    exit (1);
}

main (argc, argv)
int    argc;
char    **argv;
{
    struct    passwd    *pwd;
    uid_t    unused_uid;
    struct    stat    sb;
    enum    { in, out, unknown } in_out;
    char    *cp;
    char    *Prog;
    int    fd;
    char    buf[BUFSIZ];
    FILE    *valid;
    char    *strchr();

    if (argc != 2)
        usage ();

    if (Prog = strchr (argv[0], '/'))
        Prog++;
    else
        Prog = argv[0];

    if (strcmp ("checkin", Prog) == 0)
        in_out = in;
    else if (strcmp ("checkout", Prog) == 0)
        in_out = out;
    else
        usage ();

    if (! (valid = fopen (SHARE_FILES, "r"))) {
        fprintf (stderr,
            "no list of shared devices in %s\n", SHARE_FILES);
        exit (1);
    }
    while (fgets (buf, sizeof buf, valid)) {
        if (cp = strchr (buf, '\n'))
            *cp = '\0';

        if (strcmp (argv[1], buf) == 0)
            break;
    }
    if (feof (valid)) {
        fprintf (stderr, "unknown device: %s\n", argv[1]);
        exit (1);
    }
    if ((pwd = getpwnam (UNUSED_NAME)) == 0) {
        fprintf (stderr, "no sharable device owner\n");
        exit (1);
    }
#ifdef    HAVE_FCHOWN
    if ((fd = open (argv[1], O_RDONLY|O_NDELAY)) < 0) {
        perror (argv[1]);
        exit (1);
    }
    if (fstat (fd, &sb)) {
        perror (argv[1]);
        exit (1);
    }
    if (in_out == in && sb.st_uid != getuid () && getuid () != 0) {
        fprintf (stderr, "device not owned by invoker\n");
        exit (1);
    }
    if (in_out == out && sb.st_uid != pwd->pw_uid && getuid () != 0) {
        fprintf (stderr, "device not owned by %s\n", UNUSED_NAME);
        exit (1);
    }
    if (fchown (fd, in_out == in ? pwd->pw_uid:getuid(), sb.st_gid)) {
        perror (argv[1]);
        exit (1);
    }
    if (fchown (fd, 0)) {
        perror (argv[1]);
        exit (1);
    }
    close (fd);
#else
    if (stat (argv[1], &sb)) {
        perror (argv[1]);
        exit (1);
    }
    if (in_out == in && sb.st_uid != getuid () && getuid () != 0) {
        fprintf (stderr, "device not owned by invoker\n");
        exit (1);
    }
    if (in_out == out && sb.st_uid != pwd->pw_uid && getuid () != 0) {
        fprintf (stderr, "device not owned by %s\n", UNUSED_NAME);
        exit (1);
    }
    if (chown (argv[1], in_out == in ? pwd->pw_uid:getuid(), sb.st_gid)) {
        perror (argv[1]);
        exit (1);
    }
    if (chmod (argv[1], 0)) {
        perror (argv[1]);
        exit (1);
    }
#endif
#ifdef    HAVE_FUSER
    sprintf (buf, "fuser -k %s >> /dev/null", argv[1]);
    (void) system (buf);
#endif
    exit (0);
}
--
John F. Haugh II        | Distribution to  | UUCP: ...!cs.utexas.edu!rpp386!jfh
Ma Bell: [phone] | GEnie PROHIBITED :-) |  Domain: [e-mail]
"If liberals interpreted the 2nd Amendment the same way they interpret the
 rest of the Constitution, gun ownership would be mandatory."