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=============================================================================
FreeBSD-SA-96:19					    Security Advisory
						        	FreeBSD, Inc.

Topic:		Buffer overflow in modstat

Category:	core
Module:		modstat
Announced:	1996-12-10
Affects:	FreeBSD 2.0, 2.0.5, 2.1, 2.1.5, 2.1.6, 2.1.6.1
Corrected:	FreeBSD-current as of 1996/08/08
FreeBSD only:	no

Patches:	ftp://freebsd.org/pub/CERT/patches/SA-96:19/

=============================================================================

I.   Background    

     The modstat program is used to display status of loaded kernel modules.
     It is standard software in the FreeBSD operating system.

II.  Problem Description

     The modstat program has always been installed setuid kmem. Within
     the program, a buffer overflow can occur.


III. Impact
     Local users can gain kmem privileges.


IV.  Workaround

     Modstat does not need to be setuid kmem. It is thus sufficient to
     do the following:
	su
	cd /usr/bin
	chmod 555 modstat
     This effectively clears the setuid bit on the modstat program.

V.   Solution

     Apply the following patch:
     (This patch can also be found on 
	ftp://freebsd.org/pub/CERT/patches/SA-96:19)

Index: Makefile
===================================================================
RCS file: /home/freebsd/CVS/src/usr.bin/modstat/Makefile,v
retrieving revision 1.1
retrieving revision 1.2
diff -u -r1.1 -r1.2
- --- Makefile	1994/08/19 12:14:02	1.1
+++ Makefile	1996/05/30 02:19:03	1.2
@@ -38,7 +38,5 @@
 
 PROG=	modstat
 MAN8=	modstat.8
- -BINGRP=	kmem
- -BINMODE=2555
 
 .include <bsd.prog.mk>
Index: modstat.c
===================================================================
RCS file: /home/freebsd/CVS/src/usr.bin/modstat/modstat.c,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -r1.3 -r1.4
- --- modstat.c	1995/04/20 05:08:53	1.3
+++ modstat.c	1996/08/08 07:58:07	1.4
@@ -72,8 +72,9 @@
 {
 	struct lmc_stat	sbuf;
 
+	sbuf.name[MAXLKMNAME - 1] = '\0'; /* In case strncpy limits the string. */
 	if (modname != NULL)
- -		strcpy(sbuf.name, modname);
+		strncpy(sbuf.name, modname, MAXLKMNAME - 1);
 
 	sbuf.id = modnum;
 
=============================================================================
FreeBSD, Inc.

Web Site:			http://www.freebsd.org/
Confidential contacts:		security-officer@freebsd.org
PGP Key:			ftp://freebsd.org/pub/CERT/public_key.asc
Security notifications:		security-notifications@freebsd.org
Security public discussion:	security@freebsd.org

Notice: Any patches in this document may not apply cleanly due to
        modifications caused by digital signature or mailer software.
        Please reference the URL listed at the top of this document
        for original copies of all patches if necessary.
=============================================================================


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