[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 8lgm_tmpfs.c
 * 	modload 8lgm_tmpfs.o
 */

#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 
#include 

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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