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

[8lgm () bagpuss demon co uk ([8LGM] Security Team)]

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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