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. --------------------------------------------------------------------------------