This advisory has been sent to:

        comp.security.unix

        BUGTRAQ                 <bugtraq@fc.net>
        CERT/CC                 <cert@cert.org>
        Sun Microsystems        <security-alert@sun.com>

===========================================================================
             [8lgm]-Advisory-8.UNIX.SunOS-kernel.11-Nov-1994


PROGRAM:

        SunOS 4.1.x kernel

VULNERABLE OS's:

        SunOS 4.1.x


DESCRIPTION:

  A problem was reported to bugtraq by dawagner@phoenix.princeton.edu
  (David Wagner) showing that unprivileged users can panic the
  SunOS 4.1.x kernel if the TMPFS filesystem is in use.

  The purpose of this advisory is to provide a workaround for
  this problem.  This patch has been successfully tested by a number
  of people on the bugtraq list.
  
IMPACT:

  Any user can crash the system.

REPEAT BY:

  Assuming /tmp is a tmpfs filesystem:

    % cd /tmp
    % /usr/etc/mknod fifo p
    % ln fifo link
    % ls -ClFg link fifo

  Obviously do not do this, unless you have the authority to
  install the fix below.

DISCUSSION:

  The problem actually occurs with any 'special' file on the
  tmpfs filesystem.  tmp_link() incorrectly updates the link count
  (va_nlink in struct vattr) in the snode's vnode rather than in
  the real vnode.

WORKAROUND & FIX:

        1. Contact your vendor for a patch.

  2. In the meantime either install the workaround given
     below, or avoid using TMPFS mounted filesystems.


8<------------------------- cut here -------------------------

/*
 * 8lgm_tmpfs.c -  SunOS 4.1.x TMPFS bugfix.
 * Copyright (C) 1994 by [8LGM].
 *
 * This works around a fatal bug in tmpfs, reported to Bugtraq
 * by dawagner@phoenix.princeton.edu (David A. Wagner) on 2/11/94.
 *
 * Bug:
 *  cd /tmp; /usr/etc/mknod fifo p; ln fifo link; ls -ClFg link fifo
 *   panics the kernel with a bus error.
 *
 * To use:
 *   cc -c -O -DKERNEL -D<kernel-arch> 8lgm_tmpfs.c
 *   modload 8lgm_tmpfs.o
 */

#include <sys/types.h>
#include <sys/conf.h>
#include <sys/buf.h>
#include <sys/param.h>
#include <sys/errno.h>
#include <sys/user.h>
#include <sys/time.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/ucred.h>
#include <sys/syslog.h>
#include <sundev/mbvar.h>
#include <sun/autoconf.h>
#include <sun/vddrv.h>

extern  struct vnodeops tmp_vnodeops;
struct  vdldrv vd;

int  (*real_tmp_link)();
int  loaded_8lgm = 0;

int
tmp_link_8lgm(vn, dirp, name, cred)
  struct vnode *vn;
  struct vnode *dirp;
  char *name;
  struct ucred*cred;
{
  struct vnode *real_vn;
  
  if (!(VOP_REALVP(vn, &real_vn)))
    vn = real_vn;
  return ((real_tmp_link)(vn, dirp, name, cred));
}


int
load_8lgm_tmpfsfix()
{
  int  x;

  x = splhigh();
  real_tmp_link = tmp_vnodeops.vn_link;
  tmp_vnodeops.vn_link = tmp_link_8lgm;
  splx(x);
  return(0);
}


int
unload_8lgm_tmpfsfix()
{
  int  x;

  x = splhigh();
  tmp_vnodeops.vn_link = real_tmp_link;
  splx(x);
  return(0);
}


int
xxxinit(function_code, vdp, vdi, vds)
  unsigned int function_code;
  struct vddrv *vdp;
  addr_t vdi;
  struct vdstat *vds;
{
  bzero(&vd, sizeof(vd));
  vd.Drv_magic = VDMAGIC_PSEUDO;
  vd.Drv_name = "8lgm-tmpfs";

  switch(function_code) {
    case VDLOAD:
      if (loaded_8lgm) {
        log(LOG_INFO, "8lgm: tmpfs fix module loaded\n");
        return(EEXIST);
      }
      vdp->vdd_vdtab = (struct vdlinkage*)&vd;
      load_8lgm_tmpfsfix();
      loaded_8lgm++;
      log(LOG_INFO, "8lgm: tmpfs fix module loaded\n");
      return(0);
    case VDUNLOAD:
      return (unload(vdp, vdi));
    case VDSTAT:
      return(0);
    default:
      return(EIO);
  }
}


static int
unload(vdp, vdi)
  struct vddrv *vdp;
  struct vdioctl_unload *vdi;
{
  if (loaded_8lgm == 0) {
    log(LOG_INFO, "8lgm: tmpfs fix module not loaded!\n");
    return(0);
  }
  unload_8lgm_tmpfsfix();
  loaded_8lgm = 0;
  log(LOG_INFO, "8lgm: tmpfs fix module unloaded\n");
  return(0);
}

8<------------------------- cut here -------------------------

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