freebsd announce - Sep 1999 - FreeBSD Security Advisory: FreeBSD-SA-99:05.fts

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============================================================================FreeBSD-SA-99:05
Security Advisory
                                                                FreeBSD, Inc.

Topic:          fts library routine vulnerability

Category:       core
Module:         kernel
Announced:      1999-09-15
Affects:        FreeBSD 3.2 (and earlier)
		FreeBSD-current before the correction date.
		FreeBSD 3.2-stable before the correction date.
Corrected:      FreeBSD-3.3 RELEASE
		FreeBSD-current as of 1999/08/26
		FreeBSD-3.2-stable as of 1999/08/26
		The FreeBSD-3.3-RC series of releases are not affected.
FreeBSD only:   NO

Patches:        ftp://ftp.freebsd.org/pub/FreeBSD/CERT/patches/SA-99:05/

I.   Background

The fts library routines provide a convenient way for a program to
walk a hierarchy of files.

II.  Problem Description

The fts library functions had a buffer overflow in them where which
would lead to a core dump when periodic ran the security checking
scripts (or other scripts which traverse trees that can be controlled
by users).  periodic(3) should limit core size to zero to disable core
dumps while it is executing commands, but does not do so.  In
addition, the kernel should not follow symbolic links.

All three of these problems caused a situation where it was possible
for an attacker could create or overwrite an arbitrary file on the
system with a moderate degree of controll of its contents to cause a
problem.

III. Impact

Local users could gain root access.

IV.  Workaround

One can workaround this problem by preventing core dumps for periodic.
This solution is less than completely satisfying, since it only plugs
the known exploit hole.  None the less, this may provide a short term
stopgap solution until a new kernel and userland can be installed.

    # mv /usr/sbin/periodic /usr/sbin/periodic.bin
    # cat > /usr/sbin/periodic
    #!/bin/sh
    ulimit -c 0
    /usr/sbin/periodic.bin $*
    ^D
    # chmod 555 /usr/sbin/periodic

V.   Solution

Apply the following patches to libc and do a make world.  Please also
see the companion advisory FreeBSD-SA-99:04.core.asc in the advisories
directory of our ftp site for details on the kernel portions of this
fix.

    Index: lib/libc/gen/fts.c
    ==================================================================    RCS
file: /home/imp/FreeBSD/CVS/src/lib/libc/gen/fts.c,v
    retrieving revision 1.10
    retrieving revision 1.11
    diff -u -r1.10 -r1.11
    --- fts.c	1999/08/15 19:21:29	1.10
    +++ fts.c	1999/09/02 07:45:07	1.11
    @@ -963,6 +963,24 @@
	    return (sp->fts_path == NULL);
     }

    +static void
    +ADJUST(p, addr)
    +	FTSENT *p;
    +	void *addr;
    +{
    +	if ((p)->fts_accpath >= (p)->fts_path &&			
    +	    (p)->fts_accpath < (p)->fts_path + (p)->fts_pathlen) {
    +		if (p->fts_accpath != p->fts_path)
    +			errx(1, "fts ADJUST: accpath %p path %p",
    +			    p->fts_accpath, p->fts_path);
    +		if (p->fts_level != 0)
    +			errx(1, "fts ADJUST: level %d not 0", p->fts_level);
    +		(p)->fts_accpath =					
    +		    (char *)addr + ((p)->fts_accpath - (p)->fts_path);	
    +	}
    +	(p)->fts_path = addr;						
    +}
    +
     /*
      * When the path is realloc'd, have to fix all of the pointers in
structures
      * already returned.
    @@ -974,18 +992,18 @@
     {
	    FTSENT *p;

    -#define	ADJUST(p) {							\
    -	(p)->fts_accpath =						\
    -	    (char *)addr + ((p)->fts_accpath - (p)->fts_path);		\
    +#define	ADJUST1(p) {							\
    +	if ((p)->fts_accpath == (p)->fts_path)				\
    +		(p)->fts_accpath = (addr);				\
	    (p)->fts_path = addr;						\
     }
	    /* Adjust the current set of children. */
	    for (p = sp->fts_child; p; p = p->fts_link)
    -		ADJUST(p);
    +		ADJUST(p, addr);

	    /* Adjust the rest of the tree. */
	    for (p = sp->fts_cur; p->fts_level >= FTS_ROOTLEVEL;) {
    -		ADJUST(p);
    +		ADJUST(p, addr);
		    p = p->fts_link ? p->fts_link : p->fts_parent;
	    }
     }


============================================================================FreeBSD,
Inc.

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

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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