Integrit File Verification System

This manual corresponds to integrit version 4.1.
Copyright (C) 2006 Ed L. Cashin

Current copies should be available at the integrit homepage.

the integrit file verification system is an independent project hosted by Sourceforge.

Table of Contents

Top

1 Introduction

1.1 Description

The integrit system detects intrusion by detecting when trusted files have been altered.

By creating an integrit database (update mode) that is a snapshot of a host system in a known state, the host’s files can later be verified as unaltered by running integrit in check mode to compare current state to the recorded known state. integrit can do a check and an update simultaneously.

1.2 Normal Use

Using a product like integrit for intrusion detection is a repeating process, involving something like the following activities:

1. generate a new current-state database while checking against an old known-state database that has been protected from modification (e.g. by putting it on read-only media or on a secure server), mailing the output to a remote machine (or more)

   This step can be done unattended, since the report that integrit generates at runtime includes the checksum of the newly-generated current-state database. The output should be directed to a remote host, e.g., via a trusted sendmail binary.

   You may use a script to renice the integrit process and possibly do a sequence of runs, each with a different configuration file.

2. read the report, possibly using UN*X or XML tools to massage it into a form to your liking

   There is an example GUI viewer for integrit’s XML output in the examples directory of the distribution.

   Below please find a description of the syntax of integrit’s human-readable output format.

3. if the report looks fine, copy the new database to a secure server for export via read-only NFS, or a secure medium that can be made read-only. (saving the old one in case something goes wrong.)
4. IMPORTANT: verify that the current checksum of the database you just copied over matches the one in the report. (This shows that no one has tampered with the database since the report and the new database were generated.)
5. everything’s OK, so the new database will be the known-state database the next time you repeat this process.

2 Invoking Integrit

Here is a list of command-line arguments that may be used when invoking integrit:

-C {conffile}

Specify a runtime configuration file for integrit.

-V

Show integrit version information and exit.

-h

Show brief help.

-x

Produce XML output.

-u

Do update - create a new database that reflects the current state of the system.

-c

Do check - compare the current state of the system to a database containing a snapshot of the system when it was in a known state.

-N

Manually override specification of the current (“New”) database. Normally it is set in the configuration file.

-O

Manually override specification of the known (“Old”) database. Normally it is set in the configuration file.

-q

Lower integrit’s level of verbosity.

-v

Increase integrit’s level of verbosity.

3 Configuration File

The configuration file determines what integrit does when it runs. For that reason, it should be kept on a secure medium, like a CD-ROM or a directory that’s exported via read-only NFS from a tightly-secured machine.¹

Please note that a trailing slash is never part of a filename, including directory names. A slash is a path separator, and any other use is not supported.

3.1 Config File Elements

• comments

  The following kinds of lines in the configuration file are ignored by integrit: blank lines; lines consisting of whitespace only; lines having the # character as the first non-whitespace character.

• known database

  The location of the known database (which contains information about the previous state of the host’s files) is specified with a line like this:

       known=/root/databases/usr_known.cdb
  

• current database

  The location of the current database (the one to be generated if integrit is doing an update) is specified in a similar manner.

      current=/root/databases/usr_current.cdb
  

• the root of integrit’s check

  The root of the filetree that integrit will cover is specified on a line like this:

      root=/usr
  

  Integrit’s file tree walk starts at the root. Everything integrit checks must be under the root. In the above example, the "/boot" directory will never be checked because it is not under /usr. You can specify slash as the root and then ignore lots of directories like /tmp, /proc, and /home, or you can use multiple configuration files.

  To search multiple roots, use multiple configure files and launch multiple instances of integrit, either in sequence or in parallel, depending on your needs.

• behavior on errors

  By default integrit stops scanning at the first error. When running as root, errors usually mean severely broken permissions or media errors that the administrator should take note of immediately. When stop_on_err is set to “0” instead, integrit will try to continue as much as possible, ignoring all non-fatal errors in the process.

• rules

  Rules in the configuration file tell integrit how to treat various parts of the filesystem. You can tell integrit to ignore /proc, not to do checksums on logfiles, not to descend into /home, to ignore the modification time on /etc/issue, etc.

  Whether or not integrit descends parts of the filetree, and whether or not it does checksums, comparison of access times, etc., are specified in a compact syntax (described below) on lines like these:

      !/usr/local/useless
      !/usr/mnt/nfs
      =/usr/share/teTeX
      /usr/local/var/log SIAM
  

  We’ll get into the nitty gritty in the following sections.

3.2 Config Rule Prefixes

When integrit is running it can do several things. By specifying rules for integrit to follow, you can control its behavior. Each rule has an optional prefix or prefixes, a filename (or directory name), and a set of checks that integrit should or should not do.

A prefix comes before the filename and tells integrit something

!

An exclamation point means “ignore”.

It will cause integrit to pretend a file or directory isn’t there.

    # ignore the useless directory and its subdirectories
    !/usr/local/useless

=

An equal sign means “don’t descend”. It will cause integrit to do checks on the file itself, but if it’s a directory, integrit won’t visit its subdirectories.

This is useful for telling integrit not to bother with certain parts of a file tree.

    # don't bother with old_project's subdirectories,
    # but do perform normal checks on the directory itself
    =/usr/local/share/old_project

You can cut down drastically on database size and integrit’s runtime by ignoring parts of the filesystem that are not essential to the system, e.g., home directories.

In general, integrit is much easier to use on a daily basis if it’s just checking the most essential parts of a system. Some sysadmins, however, have told me that they enjoy getting more in touch with their systems by having integrit monitor almost everything!

$

A dollar sign prefix indicates a non-cascading rule that doesn’t get inherited by subdirectories and files as regular rules do.

    # this redhat system updates /etc/issue on boot
    # so we ignore modification and change time on /etc,
    # but we still want to monitor mtime and ctime on
    # some files and directories under this /etc.

    $ /etc     MC

3.3 Config Rule Checksets

• a set of switches

  A filename followed by a set of one-letter switches turns checks on and off, for example:

      # do check the access time, but don't do a checksum:
      /usr/local/secret/text.txt aS
  

  There are no spaces between the switches.

• switch syntax

  Upper case turns off a given check. Lower case turns it on.

  When you turn off a check, e.g. by using S for “no checksums”, then all subdirectories inherit that option: no checksums are done.

  You can always override switches that are inherited from parent directories. There is also a special dollar-sign prefix (described above) you can use to override the normal cascading behavior.

  e.g., In the example below, all the stuff under /var/log won’t have checksums done, except all the files under /var/log/archives:

      /var/log            S
      /var/log/archive    s
  

  Again, the upper case turns the check off, and the lower case turns it back on.

• list of switches

  The default checks are these: checksum; inode; permissions; number of links; uid; gid; mtime; and ctime. You can overrule the defaults by specifying all switches for the root directory in the configuration file.

  Here’s a table of letters and the corresponding checks/options:

  s

  checksum

  i

  inode

  p

  permissions

  t

  file type

  d

  device type (if file is blk or chr special)

  l

  number of links

  u

  uid

  g

  gid

  z

  file size (redundant if checksums are on)

  a

  access time

  m

  modification time

  c

  time UN*X file information was changed

  r

  reset access time (option)

4 Human Readable Output

The human-readable format is intended for quick scanning on a viewer with a large number of columns (like an xterm with maximized width).

Other popular file integrity verification systems split the information between a list of files that have changed at the top of the report and a more detailed section showing the nature of the changes at the bottom of the report. Instead, integrit provides all the information for each file as it learns it.

Besides saving on runtime memory usage, the big advantage of this approach is that the person reading the output never has to skip to the end of the report to learn the exact nature of a change.

In this output format, messages from integrit have a specific prefix showing what kind of message it is:

• “integrit: ” integrit is telling you something
• “changed: ” a file has changed somehow
• “missing: ” a file in the known database is no longer around ²
• “new: ” a file not in the known database has appeared

The one-letter characters for options and checks (see table of checkset codes) is used in the human-readable output format for reporting corresponding changes.

For example, the switch for checking permissions is p. If integrit notes that the file permissions have changed, in the output you will see this kind of line:

    changed: /etc/secret   p(640:666)

That means that the permissions (“p”) have changed from 640 to 666. In general, the syntax is as follows:

    changed: filename   x(known:current)

… where x is the one-letter symbol showing what’s changed (see list of switches), "known" is the value from the known database, and "current" is the state of the file that integrit observed at runtime.

exception:

• Symlinks have sym where the octal permissions (which would always be “777”) would be.

You can skip the preamble in the human-readable report by lowering the verbosity level with the “-q” command-line option.

5 Exit Status

Since version three, integrit’s exit status indicates whether or not it found changes.

0

When integrit returns zero to the process that started integrit, it means that no changes were detected. (Unless you are doing a check, no changes will be detected.)

1

An exit status of one means that changes were detected but no errors were encountered. (An error is a failure condition that prevents integrit from doing its job.)

2

Two signifies that an error occured, and integrit was not able to do its job. When stop_on_err is “0” and a check is performed, an exit status of two means that some errors were encountered during the scan, but no changes could be found.

3

Both errors and changes were found.

6 Auxiliary Tools

The integrit source distribution comes with two standalone tools. You do not need to be familiar with these tools in order to use integrit, but I personally find them to be very convenient once in a while.

The tools are i-viewdb and i-ls.

6.1 i-viewdb

To detect file deletions, modifications, and creations, integrit saves information about your files in databases. i-viewdb is a standalone tool that allows you to view the information stored in integrit databases. It only has one option:

-s

Do not show the checksums stored in the database.

… and you invoke it like this:

    i-viewdb [-s] {dbname}

… where “dbname” is the name of the integrit database for i-viewdb to examine.

The output syntax is the same as that of integrit.

Examples:

   i-viewdb integrit-foo.cdb | less

… uses the "less" pager to view contents of the integrit database.

   i-viewdb integrit-foo.cdb | awk '{ print $1 " " $8 }'

… look at the files and access times in the integrit database.

6.2 i-ls

The integrit system detects intrusion by detecting when trusted files have been altered.

Integrit records information about files in a database when it does an update and compares that information to live files when it does a check.

The i-ls standalone tool allows the user to see that same information for live files.

The output syntax is similar to that of integrit.

Options:

-s

Do not show/calculate a checksums for all regular files. In case i-ls cannot do a checksum (e.g. permission denied), a warning is issued.

It is invoked like this:

    i-ls [-s] {filename|dirname} [filename|dirname] ...

You specify a filename for i-ls to examine, or you specify a directory to have i-ls examine all the files in the directory.

Examples:

     i-ls /tmp/foo.txt /tmp/bar.txt

… shows file stat attributes for the file, /tmp/foo.txt and also for /tmp/bar.txt.

     i-ls /tmp

… shows file stat attributes for all files in the directory, /tmp.

     i-ls -s /tmp

… shows file stat attributes for all files in the directory, /tmp, omitting SHA-1 checksum information.

7 FAQ

7.1 Win32

Q: What about Win32 support?

A few people have asked about Win32 support. In short, go for it. I get the impression that it’s not something that a lot of people have done, and I’m not much of a Windows user, but I did it just to see what would happen.

A helpful soul pointed out that it is still (Windows 2000) not possible to create a directory named "aux" in Windows (a DOS-ism like "prn" and "nul"), and so integrit’s aux directory has been renamed to "utils" since version three to accomodate the limitation. Since then it’s been theoretically possible to build integrit on Windows.

Version 3.03 integrit on Windows XP using Cygwin 1.3.12-2 builds cleanly and passes the “make test”. Your mileage may vary.

7.2 Regular Expressions

Q: What about regular expressions in the conf file?

It usually occurs to an integrit user at some point, "Wouldn’t it be nice to use regular expressions in the integrit configuration file instead of literal paths?" The answer is that, yes, that would be convenient, but it isn’t likely to happen.

The added runtime cost of compiling regular expression objects and evaluating all the pathnames would be substantial, and it would make integrit more complex. Better to leave integrit stable and simple and then list files explicitly in the configuration file.

After all, you have all kinds of unix tools (find, grep, etc.), that can help you create the configuration file by using regular expressions!

7.3 Trailing Slash

Q: Why does integrit scan /proc when I put "! /proc/" in the configuration file?

Trailing slashes aren’t really part of a directory’s name. Leave them out in the configuration file.

For example, to ignore /var/tmp, this will work:

    ! /tmp

... but this will not:

    # WRONG: trailing slash
    ! /tmp/

7.4 Missing Files

Q: When I do a check only, -c and no -u, I get an error:

   integrit: not doing update, so no check for missing files

Just use both "-c" and "-u". This is the fastest, simplest way to be able to check for missing files. If integrit is creating a new current-state database, then at the end of the run it has all the information it needs to tell you what files are missing.

The good news is that it takes almost the same amount of time to do check and update simultaneously as it would to do one or the other. wouldn’t be gaining anything by running check by itself.

7.5 Large Files

Q: Why does integrit crash on encountering files of greater than five gigabytes in size?

It’s a platform-dependent thing.

Many Operating Systems are in the process of developing support for large files. If you see integrit fail when it encounters large files, then large file support is what you need.

Since version 3.02, integrit has large file support turned on by default (via the autoconf-generated configure script), but you still need to make sure your system can handle large files.

For Linux-based systems, there is a good document here:

http://www.suse.de/~aj/linux_lfs.html

In a nutshell, if you are using gcc and Linux, then if your using a 2.4.x and an ext2 filesystem that was created under a 2.4.x kernel, then you should be OK with integrit versions 3.02 and later.

For general information, here is a resource:

http://www.sas.com/standards/large.file/x_open.20Mar96.html

Your system should have documentation explaining how to get large file support.

7.6 Multiple Roots

Q: Wouldn’t it be nicer if we could put multiple roots in one integrit config file?

A: Perhaps, but not much nicer, and it would complicate integrit internally.

Say you want to ignore all of /usr/local in your integrit-root.conf configuration file, but you want to check /usr/local/etc. You can create another configuration file, integrit-usr_local_etc.conf, with “root=/usr/local/etc” in it.

Then simply run integrit twice. You can even run two integrits in parallel if /usr/local/etc is on a different device than the other areas and you have the CPU and memory to spare.

It is very easy to generate multiple configuration files from a master configuration file using UN*X tools. It’s also easy to create a statically-linked program that does fork and execl to run multiple integrits. There’s an example in the examples directory of the integrit distribution: integrit-run.c.

Appendix A Resources

To get the latest integrit, check the integrit homepage:

    http://integrit.sourceforge.net/

There are many resources at integrit’s project page on sourceforge, including mailing lists and a web-interface for the source in CVS.

    http://sourceforge.net/projects/integrit

Appendix B GNU GENERAL PUBLIC LICENSE

Copyright © 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111, USA

Everyone is permitted to copy and distribute verbatim copies
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How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.

To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively convey the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.

one line to give the program's name and an idea of what it does.
Copyright (C) 19yy  name of author

This program is free software; you can redistribute it and/or
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as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.

This program 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 General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111, USA.

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this when it starts in an interactive mode:

Gnomovision version 69, Copyright (C) 19yy name of author
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
type `show w'.  This is free software, and you are welcome
to redistribute it under certain conditions; type `show c' 
for details.

The hypothetical commands ‘show w’ and ‘show c’ should show the appropriate parts of the General Public License. Of course, the commands you use may be called something other than ‘show w’ and ‘show c’; they could even be mouse-clicks or menu items—whatever suits your program.

You should also get your employer (if you work as a programmer) or your school, if any, to sign a “copyright disclaimer” for the program, if necessary. Here is a sample; alter the names:

Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written 
by James Hacker.

signature of Ty Coon, 1 April 1989
Ty Coon, President of Vice

This General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Library General Public License instead of this License.

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