Bell Labs libsafe-2.0, detection and protection against stack smashing and
format string attacks.

// Copyright (C) 2000 Avaya Labs, Avaya Inc.
// Copyright (C) 1999 Bell Labs, Lucent Technologies.
// Copyright (C) Arash Baratloo, Timothy Tsai, and Navjot Singh.
//
// This file is part of the Libsafe library.
// Libsafe version 2.x: protecting against stack smashing attacks.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// 
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
// 
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
//
// For more information, 
//   visit http://www.research.avayalabs.com/project/libsafe/index.html
//   or email libsafe@research.avayalabs.com

The libsafe-1.3 library protects a process against the exploitation of buffer
overflow vulnerabilities in process stacks.  Libsafe-2.0 adds the capability of
protecting against format string exploits.  [See Note 1.] Libsafe works with
any existing pre-compiled executable and can be used transparently, even on a
system-wide basis.  The method intercepts all calls to library functions that
are known to be vulnerable.  A substitute version of the corresponding function
implements the original functionality, but in a manner that ensures that any
buffer overflows are contained within the current stack frame.  Libsafe has
been shown to detect several known attacks and can potentially prevent yet
unknown attacks.  Experiments indicate that the performance overhead of libsafe
is negligible.

The following unsafe functions are currently monitored by libsafe:

              strcpy(char *dest, const char *src)
                     May overflow the dest buffer.

              strcat(char *dest, const char *src)
                     May overflow the dest buffer.

              getwd(char *buf)
                     May overflow the buf buffer.

              gets(char *s)
                     May overflow the s buffer.

              [vf]scanf(const char *format, ...)
                     May overflow its arguments.

              realpath(char *path, char resolved_path[])
                     May overflow the path buffer.

              [v]sprintf(char *str, const char *format, ...)
                     May overflow the str buffer.



For more information see libsafe/doc/libsafe.8.html.

--------------------------------------------------
Note 1:   Tim Robbins has created an alternative solution to detecting format
string attacks.  Tim's solution is called libformat.  Both libformat and
libsafe use function interception via shared libraries to sanity check function
arguments, but the particular methods for checking arguments differ.  See
http://box3n.gumbynet.org/~fyre/software/libformat.php3 for more information.


SLACKWARE NOTES (this section added by volkerdi@slackware.com)

       While testing libsafe on Slackware, I noticed a couple of minor
       problems:

       o  libsafe breaks libc4 and libc5 dynamic binaries.
          This shouldn't be too much of a surprise, since it preloads against
          everything.  If it could be made to load only against glibc2
          binaries, this problem would be solved.

       o  libsafe may break a few programs.  For example, we found that the
          'xv' image program would segfault when libsafe was preloaded.

       Because of these problems (especially the first one) it was decided that
       libsafe.tgz should be placed in the /contrib directory as an optional
       package rather than merged into the base (A) series.  However, don't
       think that's because we're not impressed with libsafe. :)  Most people
       don't have a need for libc4 and libc5 compatability, and xv can always
       be recompiled statically to work around the problem.  I run libsafe on
       my server/router box, and have experienced no problems with it.  In an
       environment where security is important, libsafe is highly recommended.

       To install on Slackware, simply use installpkg:

           installpkg libsafe.tgz

       New processes that are started after the package is installed will
       be automatically protected.  To get protection on things like sendmail
       and other daemons, you'll need to restart them (or just reboot your
       machine).

       Libsafe must be uninstalled manually.  To uninstall it, follow this
       procedure (carefully):

           1.  remove /lib/libsafe.so.2 from /etc/ld.so.preload
           2.  reboot
           3.  remove /lib/libsafe.so.2 and /lib/libsafe.so.2.0

HOMEPAGE

       The home web page for libsafe is:
         http://www.research.avayalabs.com/project/libsafe