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DOC: additional pass over DEVELOP (just rephrasings, spaces, formatting)

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Yaroslav Halchenko 2013-09-25 22:12:36 -04:00
parent 3d6fa59b53
commit e9504122b8
1 changed files with 148 additions and 134 deletions
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@ -1,6 +1,6 @@
__ _ _ ___ _
/ _|__ _(_) |_ ) |__ __ _ _ _
| _/ _` | | |/ /| '_ \/ _` | ' \
__ _ _ ___ _
/ _|__ _(_) |_ ) |__ __ _ _ _
| _/ _` | | |/ /| '_ \/ _` | ' \
|_| \__,_|_|_/___|_.__/\__,_|_||_|
================================================================================
@ -26,7 +26,7 @@ Pull Requests
When submitting pull requests on GitHub we ask you to:
* Clearly describe the problem you're solving;
* Don't introduce regressions that will make it hard for systems administrators
* Don't introduce regressions that will make it hard for systems administrators
to update;
* If adding a major feature rebase your changes on master and get to a single commit;
* Include test cases (see below);
@ -42,74 +42,79 @@ Filters are tricky. They need to:
* work with the range of logging configuration options available in the
software;
* work with multiple operating systems;
* not make assumptions about the log format in excess of the software (don't
assume a username doesn't contain spaces and use \S+ unless you've checked
the source code);
* make assumptions as to how future versions of the software will log messages
(guess what would happen to the log message if different authentication
* not make assumptions about the log format in excess of the software
(e.g. do not assume a username doesn't contain spaces and use \S+ unless
you've checked the source code);
* account for how future versions of the software will log messages
(e.g. guess what would happen to the log message if different authentication
types are added);
* not be susceptible to DoS vulnerabilities (see Filter Security below); and
* match intended log lines only.
Please follow the steps from Filter Test Cases to Developing Filter Regular
Expressions and submit a GitHub pull request afterwards. If you get stuck,
create a GitHub issue with what you have done and we'll attempt to help.
Expressions and submit a GitHub pull request (PR) afterwards. If you get stuck,
you can push your unfinished changes and still submit a PR -- describe
what you have done, what is the hurdle, and we'll attempt to help (PR
will be automagically updated with future commits you would push to
complete it).
Filter test cases
-----------------
Purpose:
Start by finding the log messages that the application generates related to
Start by finding the log messages that the application generates related to
some form of authentication failure. If you are adding to an existing filter
think about whether the log messages are of a similar importance and purpose
to the existing filter. If you are a user of fail2ban, and did a package
update of fail2ban that started matching the new log messages, would anything
unexpected happen? Would the bantime/findtime for the jail be appropriate for
the new log messages. If it doesn't perhaps it needs to be in a separate
filter definition, for example like exim is authentication failures and
exim-spam contains log messages related to spam.
to the existing filter. If you were a user of Fail2Ban, and did a package
update of Fail2Ban that started matching new log messages, would anything
unexpected happen? Would the bantime/findtime for the jail be appropriate for
the new log messages? If it doesn't, perhaps it needs to be in a separate
filter definition, for example like exim filter aims at authentication failures
and exim-spam at log messages related to spam.
Even if it is a new filter you may consider separating the log messages into
different filters based on purpose.
Cause:
Are some of the log lines a result of the same action? For example is a PAM
Are some of the log lines a result of the same action? For example, is a PAM
failure log message, followed by an application specific failure message the
result of the same user/script action. The result is if you add regular
expressions for both you'll end up with two failures for a single action.
Select the most appropriate log message and document the other log message with
a test case not to match it and a description as to why you chose one over
another.
result of the same user/script action? If you add regular expressions for
both you would end up with two failures for a single action.
Therefore, select the most appropriate log message and document the other log
message) with a test case not to match it and a description as to why you chose
one over another.
With the log lines selected consider what occurred to generate those log
messages and whether they could of been generated by accidental means. Could
the log message occur always as this is the first step towards the application
With the selected log lines consider what action has caused those log
messages and whether they could have been generated by accident? Could
the log message be occurring due to the first step towards the application
asking for authentication? Could the log messages occur often? If some of
these are true make a note of this in the jail.conf example that you provide.
Samples:
Its important to include log file samples so any future change in the regular
It is important to include log file samples so any future change in the regular
expression will still work with the log lines you have identified.
The sample log messages are provided in testcases/files/logs/ with same name
as the filter. Each log line should include a failJSON metadata (so the logs
The sample log messages are provided in a file under testcases/files/logs/
named identically as the corresponding filter (but without .conf extension).
Each log line should be preceded by a line with failJSON metadata (so the logs
lines are tested in the test suite) directly above the log line. If there is
any specific information about the log message, such as version or an
application configuration option that is needed for the message to occur,
application configuration option that is needed for the message to occur,
include this in a comment (line beginning with #) above the failJSON metadata.
Log samples should include only one, definitely not more than 3, examples of
log messages of the same form. If log messages are different in different
versions of the application log messages that show this is encouraged.
versions of the application log messages that show this are encouraged.
Also attempt inject an IP into the application so that fail2ban detects the IP
Also attempt to inject an IP into the application (e.g. by specifying
it as a username) so that Fail2Ban possibly detects the IP
from user input rather than the true origin. See the Filter Security section
and the top example in testcases/files/logs/apache-auth as to how to do this.
One you have discovered this correct the regex so it doesn't match and provide
this as a test case with match: false (see failJSON below).
One you have discovered that this is possible, correct the regex so it doesn't
match and provide this as a test case with "match": false (see failJSON below).
If the mechanism to create the log message isn't obvious provide a
configuration and/or sample scripts testcases/files/config/{filtername} and
@ -120,24 +125,25 @@ FailJSON metadata:
A failJSON metadata is a comment immediately above the log message. It will
look like:
# failJSON: { "time": "2013-06-10T10:10:59", "match": true , "host": "193.169.56.211" }
# failJSON: { "time": "2013-06-10T10:10:59", "match": true , "host": "93.184.216.119" }
Time should match the time of the log message. It is in a specific format of
Year-Month-Day'T'Hour:minute:Second. If your log message does not include a
year, like the example below, the year will be 2005, if before Sun Aug 14 10am
UTC, and 2004 if afterwards.
Year-Month-Day'T'Hour:minute:Second. If your log message does not include a
year, like the example below, the year should be listed as 2005, if before Sun
Aug 14 10am UTC, and 2004 if afterwards. Here is an example failJSON
line preceding a sample log line:
# failJSON: { "time": "2005-03-24T15:25:51", "match": true , "host": "198.51.100.87" }
Mar 24 15:25:51 buffalo1 dropbear[4092]: bad password attempt for 'root' from 198.51.100.87:5543
The host will contain the IP or domain that should be blocked.
The "host" in failJSON should contain the IP or domain that should be blocked.
For long lines that you don't want matched, like log injection vulnerabilities
and log lines excluded (see "Cause" section above), a "match": false in the
failJSON and the reason why in the comment above.
For long lines that you do not want to be matched (e.g. from log injection
attacks) and any log lines to be excluded (see "Cause" section above), set
"match": false in the failJSON and describe the reason in the comment above.
After developing the regexs, the following command will test all the failJSON
metadata against the log lines:
After developing regexes, the following command will test all failJSON metadata
against the log lines in all sample log files
./fail2ban-testcases testSampleRegex
@ -146,28 +152,29 @@ Developing Filter Regular Expressions
Date/Time:
The first step in checking your log line can have a filter is to check that the
time format matches an existing regex. To test this copy the time component
from the log line and append an IP address. Then test it with:
At the moment, Fail2Ban depends on log lines to have time stamps. That is why
before starting to develop failregex, check if your log line format known to
Fail2Ban. Copy the time component from the log line and append an IP address to
test with following command:
./fail2ban-regex "2013-09-19 02:46:12 1.2.3.4" "<HOST>"
In the output from this should be something like:
Output of such command should contain something like:
Date template hits:
|- [# of hits] date format
| [1] Year-Month-Day Hour:Minute:Second
Ensure that the template description matches of bits in the time format. If
there isn't a matched a format and date regex can be added to
server/datedetector.py. Ensure this is added in an order that will match make
more specific matches occur first and that their is no confusion as to which
is the date or month.
Ensure that the template description matches time/date elements in your log line
time stamp. If there is no matched format then date template needs to be added
to server/datedetector.py. Ensure that a new template is added in the order
that more specific matches occur first and that there is no confusion between a
Day and a Month.
Filter file:
The filter file is in config/filter.d/{filtername}.conf. The format of the
filter file has two sections INCLUDES and Definition as follows:
The filter is specified in a config/filter.d/{filtername}.conf file. Filter file
can have sections INCLUDES (optional) and Definition as follows:
[INCLUDES]
@ -181,30 +188,31 @@ failregex = ....
ignoreregex = ....
This is also documented in the man pages as jail.conf (section 5). Other
definitions can be added to make failregex's more readable and maintainable.
This is also documented in the man page jail.conf (section 5). Other definitions
can be added to make failregex's more readable and maintainable to be used
through string Interpolations (see http://docs.python.org/2.7/library/configparser.html)
General rules:
Use "before" if you need to include a common set of rules, like syslog or if
there's a common set of regexs for multiple filters.
there is a common set of regexes for multiple filters.
Use "after" if you wish to allow the user to overwrite a set of customisation's
Use "after" if you wish to allow the user to overwrite a set of customisations
of the current filter. This file doesn't need to exist.
Try to avoid using ignoreregex mainly for performance reasons. The case when
you would use it is if in trying to avoid using ignoreregex, you end up with
an unreadable failregex.
Try to avoid using ignoreregex mainly for performance reasons. The case when you
would use it is if in trying to avoid using it, you end up with an unreadable
failregex.
Syslog:
If your application logs to syslog you can use the following to capture that
part. So as a base use:
If your application logs to syslog you can take advantage of log line prefix
definitions present in common.conf. So as a base use:
[INCLUDES]
before = commmon.conf
before = common.conf
[Definition]
@ -213,113 +221,119 @@ _daemon = app
failregex = ^%(__prefix_line)s
In this example common.conf defines __prefix_line which also contains the
_daemon name, (in syslog terms the service) you specified. _daemon can also be
a regex.
_daemon name (in syslog terms the service) you have just specified. _daemon
can also be a regex.
So the following uses a _daemon set to "dovecot"
For example, to capture following line _daemon should be set to "dovecot"
Dec 12 11:19:11 dunnart dovecot: pop3-login: Aborted login (tried to use disabled plaintext auth): rip=190.210.136.21, lip=113.212.99.193
So now ^%(__prefix_line)s matches "Dec 12 11:19:11 dunnart dovecot: ". Note it
matches the trailing space. Putting a space after ^%(__prefix_line)s in the
regex will probably not match.
and then ^%(__prefix_line)s would match "Dec 12 11:19:11 dunnart dovecot:
". Note it matches the trailing space(s) as well.
Substitutions:
Substitutions (AKA string interpolations):
Substation's are what the syslog uses. The regex bits of %(_name)s substitute
the _name definition into the regex. They are useful for making the regexes
more readable and also defining regex parts that occur in multiple log lines.
We have used string interpolations in above examples. They are useful for
making the regexes more readable, reuse generic patterns in multiple failregex
lines, and also to refer definition of regex parts to specific filters or even
to the user. General principle is that value of a _name variable replaces
occurrences of %(_name)s within the same section or anywhere in the config file
if defined in [DEFAULT] section.
Regular Expressions:
The regular expression you will be writing will assume that the date/time has
been removed from the log line because this is how fail2ban works internally.
Regular expressions (failregex, ignoreregex) assume that the date/time has been
removed from the log line (this is just how fail2ban works internally ATM).
If the format is like '<date...> error 1.2.3.4 is evil' then you will need to
match the < at the start so regex should be similar to '^<> <HOST> is evil$'.
Use <HOST> where the IP/domain name appears in the log line.
If the format is like '<date...> error 1.2.3.4 is evil' then you need to match
the < at the start so regex should be similar to '^<> <HOST> is evil$' using
<HOST> where the IP/domain name appears in the log line.
The following general rules apply to regular expressions:
* Ensure regexs start with a ^ and are restrictive as possible. E.g. not .* if
\d+ is sufficient
* Use the functionality of regexs http://docs.python.org/2/library/re.html
* Try to make the regular expression readable (as much as possible). E.g.
(?:...) represents a non-capturing regex but (...) is more readable.
* ensure regexes start with a ^ and are as restrictive as possible. E.g. do not
use .* if \d+ is sufficient;
* use functionality of Python regexes defined in the standard Python re library
http://docs.python.org/2/library/re.html;
* make regular expressions readable (as much as possible). E.g.
(?:...) represents a non-capturing regex but (...) is more readable, thus
preferred.
If you only have a basic knowledge of regular repressions read
http://docs.python.org/2/library/re.html first. Really. It doesn't take long
and will remind you which bits you need to escape and which bits you don't.
If you have only a basic knowledge of regular repressions we advise to read
http://docs.python.org/2/library/re.html first. It doesn't take long and would
remind you e.g. which characters you need to escape and which you don't.
Developing/testing the regex:
Developing/testing a regex:
You can develop the regex in the file or on the command line depending on your
preference. You can also use the samples you've created in the test cases or
test them one at a time.
You can develop a regex in a file or using command line depending on your
preference. You can also use samples you have already created in the test cases
or test them one at a time.
The general tool is fail2ban-regex. To see how to use it run:
The general tool for testing Fail2Ban regexes is fail2ban-regex. To see how to
use it run:
./fail2ban-regex --help
./fail2ban-regex --help
Take note of -l heavydebug / -l debug and -v as they will be most useful.
Take note of -l heavydebug / -l debug and -v as they might be very useful.
TIP: Take a look at the source code of the application. You may see optional or
extra log messages, or parts there of, that need to form part of your regex.
It may also show how some parts are con trained and different formats
depending on configuration or less common usages.
TIP: Take a look at the source code of the application you are developing
failregex for. You may see optional or extra log messages, or parts there
of, that need to form part of your regex. It may also reveal how some
parts are constrained and different formats depending on configuration or
less common usages.
TIP: Some applications log spaces at the end. If you're not sure add \s*$ as the
end part of the regex.
TIP: Some applications log spaces at the end. If you are not sure add \s*$ as
the end part of the regex.
If your regex isn't matching take a look at http://www.debuggex.com/?flavor=python
If your regex is not matching, http://www.debuggex.com/?flavor=python can help
to tune it:
Using the regex from the ./fail2ban-regex output (to ensure all substitutions
are done) and with <HOST> replaced with (?&.ipv4). Set the regex type to
Python.
For the test data put your log output with the time removed.
When you've fixed the regex put it back into your filter file.
* use regex from the ./fail2ban-regex output (to ensure all substitutions are
done) and replace <HOST> with (?&.ipv4). Make sure that regex type set to
Python;
* for the test data put your log output with the time removed;
- when you have fixed the regex put it back into your filter file.
Please spread the good word about debuggex - Serge Toarca is kindly continuing
its free availability to Open Source developers.
Finishing up:
If you've created a new filter, add an entry in config/jail.conf. The theory
here is that a user will create a jail.conf with [filtername]\nenable=true.
If you've added a new filter, add a new entry in config/jail.conf. The theory
here is that a user will create a jail.local with [filtername]\nenable=true to
enable your jail.
So more specifically in the [filter] section in jail.conf:
* Ensure that you have "enabled = false", we want people to enable as needed
* use "filter =" set to your filter name.
* use a action to disable ports associated with the application
* set "logpath" to a usual location for the log file for the application.
* If the default findtime or bantime isn't appropriate to the filter set a value
that is more appropriate.
* ensure that you have "enabled = false" (users will enable as needed);
* use "filter =" set to your filter name;
* use a typical action to disable ports associated with the application;
* set "logpath" to the usual location of application log file;
* if the default findtime or bantime isn't appropriate to the filter, specify
more appropriate choices (possibly with a brief comment line).
Send the fail2ban a git pull request (See "Pull Requests" above) containing
your great work.
Submit github pull request (See "Pull Requests" above) for
github.com/fail2ban/fail2ban containing your great work.
Filter Security
---------------
Poor filter regular expressions are susceptible to DoS attacks.
When a remote user has the ability to introduce text that will match the
filter regex, such that the inserted text matches the <HOST> part, they have the
When a remote user has the ability to introduce text that would match filter's
failregex, while matching inserted text to the <HOST> part, they have the
ability to deny any host they choose.
So the <HOST> part must be anchored on text generated by the application, and not
the user, to a sufficient extent that the user cannot insert the entire text.
So the <HOST> part must be anchored on text generated by the application, and
not the user, to a extent sufficient to prevent user inserting the entire text
matching this or any other failregex.
Ideally filter regex should anchor to the beginning and end of the log line
however as more applications log at the beginning than the end, anchoring the
Ideally filter regex should anchor at the beginning and at the end of log line.
However as more applications log at the beginning than the end, anchoring the
beginning is more important. If the log file used by the application is shared
with other applications, like system logs, ensure the other application that
use that log file do not log user generated text at the beginning of the line,
or, if they do, ensure the regexs of the filter are sufficient to mitigate the
risk of insertion.
with other applications, like system logs, ensure the other application that use
that log file do not log user generated text at the beginning of the line, or,
if they do, ensure the regexes of the filter are sufficient to mitigate the risk
of insertion.
Examples of poor filters
@ -714,11 +728,11 @@ ver. 0.8.12 (2013/XX/XXX) - wanna-be-released
-----------
- Fixes:
- New Features:
- Enhancements:
and adjust common/version.py to carry .dev suffix to signal
a version under development.