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AUDIT.RULES:(7)         System Administration Utilities        AUDIT.RULES:(7)

NAME
       audit.rules - a set of rules loaded in the kernel audit system

DESCRIPTION
       audit.rules is a file containing audit rules that will be loaded by the
       audit daemon's init script whenever the daemon is started. The auditctl
       program  is used by the initscripts to perform this operation. The syn-
       tax for the rules is essentially the same as when typing in an auditctl
       command  at  a shell prompt except you do not need to type the auditctl
       command name since that is implied. The audit rules  come  in  3  vari-
       eties: control, file, and syscall.

   Control
       Control  commands generally involve configuring the audit system rather
       than telling it what to watch for.  These  commands  typically  include
       deleting  all  rules,  setting  the size of the kernel's backlog queue,
       setting the failure mode, setting the event  rate  limit,  or  to  tell
       auditctl  to  ignore  syntax  errors in the rules and continue loading.
       Generally, these rules are at the top of the rules file.

   File System
       File System rules are sometimes called watches. These rules are used to
       audit  access to particular files or directories that you may be inter-
       ested in. If the path given in the rule is a directory, then  the  rule
       used  is  recursive  to  the bottom of the directory tree excluding any
       directories that may be mount points. The syntax of these rules  gener-
       ally follow this format:

       -w path-to-file -p permissions -k keyname

       where the permission are any one of the following:

              r - read of the file

              w - write to the file

              x - execute the file

              a - change in the file's attribute

   System Call
       The system call rules are loaded into a matching engine that intercepts
       each syscall that all programs on the system  makes.  Therefore  it  is
       very  important  to only use syscall rules when you have to since these
       affect performance. The more rules, the bigger the performance hit. You
       can  help  the performance, though, by combining syscalls into one rule
       whenever possible.

       The Linux kernel has 5 rule matching lists or filters as they are some-
       times  called. They are: task, entry, exit, user, and exclude. The task
       list is checked only during the fork or clone syscalls.  It  is  rarely
       used in practice.

       The  entry  list is run through at each syscall entry. The exit list is
       checked on syscall exit. The main difference between these two is  that
       some  things  are not available at syscall entry and cannot be checked,
       like the exit value. Rules on the exit filter are much more common  and
       all  fields are available for use at syscall exit. At some point in the
       near future the entry filter will be deprecated, so it would be best to
       only use the exit filter.

       The  user  filter  is used to filter some events that originate in user
       space. Fields that are valid for use are: uid, auid, gid, and  pid. The
       exclude  filter  is  used to exclude certain events from being emitted.
       The msgtype field is used to tell the kernel which message types you do
       not want to record.

       Syscall rules take the general form of:

       -a action,list -S syscall -F field=value -k keyname

       The  -a  option tells the kernel's rule matching engine that we want to
       append a rule and the end of the rule list.  But  we  need  to  specify
       which  rule  list  it goes on and what action to take when it triggers.
       Valid actions are:

              always - always create an event

              never  - never create an event

       The action and list are separated by a comma but no space  in  between.
       Valid  lists  are:  task, entry, exit, user, and exclude. There meaning
       was explained earlier.

       Next in the rule would normally be the -S option. This field can either
       be  the  syscall  name  or  number. For readability, the name is almost
       always used. You may give more that one syscall in a rule by specifying
       another  -S  option.  When sent into the kernel, all syscall fields are
       put into a mask so that one compare can determine if the syscall is  of
       interest.  So,  adding multiple syscalls in one rule is very efficient.
       When you specify a syscall name, auditctl will look up the name and get
       its  syscall  number.  This leads to some problems on bi-arch machines.
       The 32 and 64 bit syscall numbers sometimes, but not  always  line  up.
       So,  to  solve this problem, you would generally need to break the rule
       into 2 with one specifying -F arch=b32  and  the  other  specifying  -F
       arch=b64.  This  needs  to go infront of the -S option so that auditctl
       looks at the right lookup table when returning the number.

       After the syscall is specified, you would normally have one or more  -F
       options  that fine tune what to match against. Rather than list all the
       valid field types here, the reader should look at the auditctl man page
       which has a full listing of each field and what it means. But its worth
       mentioning a couple things.

       The audit system considers uids to be unsigned numbers. The audit  sys-
       tem  uses  the  number  -1 to indicate that a loginuid is not set. This
       means that when its printed out, it looks like 4294967295. If you write
       a  rule  that  you wanted try to get the valid users over 500, then you
       would also need to take into account that the representation of  -1  is
       higher  than 500. So you would address this with the following piece of
       a rule:

       -F auid>=500 -F auid!=4294967295

       These rules are "anded" and both have to be true.

       The last thing to know about syscall rules is that you can  add  a  key
       field  which is a free form text string that you want inserted into the
       event to help identify its meaning. This is discussed in more detail in
       the NOTES section.

NOTES
       The  purpose  of auditing is to be able to do an investigation periodi-
       cally or whenever an incident occurs. A few simple steps in planning up
       front will make this job easier. The best advice is to use keys in both
       the watches and system call rules to give the rule a meaning. If  rules
       are  related  or together meet a specific requirement, then give them a
       common key name. You can use this during your investigation  to  select
       only results with a specific meaning.

       When doing an investigation, you would normally start off with the main
       aureport output to just get an idea about what is happening on the sys-
       tem.  This  report mostly tells you about events that are hard coded by
       the audit system such as  login/out,  uses  of  authentication,  system
       anomalies, how many users have been on the machine, and if SE Linux has
       detected any AVCs.

       aureport --start this-week

       After looking at the report, you probably want to  get  a  second  view
       about  what  rules  you loaded that have been triggering. This is where
       keys become important. You would generally run the key  summary  report
       like this:

       aureport --start this-week --keys --summary

       This  will  give  an  ordered listing of the keys associated with rules
       that have been triggering. If, for example, you  had  a  syscall  audit
       rule  that triggered on the failure to open files with EPERM that had a
       key field of access like this:

       -a always,exit -F arch=b64 -S open -F exit=-EPERM -k access

       Then you can isolate these failures with ausearch and pipe the  results
       to  aureport  for  display. Suppose your investigation noticed a lot of
       the access denied events. If you wanted to see the files that  unautho-
       rized access has been attempted, you could run the following command:

       ausearch --start this-week -k access --raw | aureport --file --summary

       This  will  give an ordered list showing which files are being accessed
       with the EPERM failure. Suppose you wanted to see which users might  be
       having failed access, you would run the following command:

       ausearch --start this-week -k access --raw | aureport --user --summary

       If  your  investigation showed a lot of failed accesses to a particular
       file, you could run the following report to see who is doing it:

       ausearch --start this-week -k access -f /path-to/file --raw |  aureport
       --user -i

       This  report will give you the individual access attempts by person. If
       you needed to see the actual audit event that is  being  reported,  you
       would look at the date, time, and event columns. Assuming the event was
       822 and it occurred at 2:30 on 09/01/2009 and you  use  the  en_US.utf8
       locale, the command would look something like this:

       ausearch --start 09/01/2009 02:30 -a 822 -i --just-one

       This will select the first event from that day and time with the match-
       ing event id and interpret the numeric values into human readable  val-
       ues.

       The  most  important  step in being able to do this kind of analysis is
       setting up key fields when the rules were originally written. It should
       also  be  pointed out that you can have more than one key field associ-
       ated with any given rule.

TROUBLESHOOTING
       If you are not getting events on  syscall  rules  that  you  think  you
       should, try running a test program under strace so that you can see the
       syscalls. There is a chance that you might have  identified  the  wrong
       syscall.

       If  you get a warning from auditctl saying, "32/64 bit syscall mismatch
       in line XX, you should specify an arch". This means that you  specified
       a  syscall  rule  on a bi-arch system where the syscall has a different
       syscall number for the 32 and 64 bit interfaces. This means that on one
       of those interfaces you are likely auditing the wrong syscall. To solve
       the problem, re-write the rule as two  rules  specifying  the  intended
       arch for each rule. For example,

       -always,exit -S open -k access

       would be rewritten as

       -always,exit -F arch=b32 -S open -k access
       -always,exit -F arch=b64 -S open -k access

       If  you  get  a warning that says, "entry rules deprecated, changing to
       exit rule". This means that you have a rule intended for the entry fil-
       ter,  but that filter is not going to be available at some point in the
       future. Auditctl moved your rule to the exit filter  so  that  its  not
       lost.  But  to  solve this so that you do not get the warning any more,
       you need to change the offending rule from entry to exit.

EXAMPLES
       The following rule shows how to audit failed access to files  due  per-
       mission  problems.  Note  that  it takes two rules for each arch ABI to
       audit this since file access can fail with two different failure  codes
       indicating permission problems.

       -a always,exit -F arch=b32 -S open -S openat -F exit=-EACCES -k access
       -a always,exit -F arch=b32 -S open -S openat -F exit=-EPERM -k access
       -a always,exit -F arch=b64 -S open -S openat -F exit=-EACCES -k access
       -a always,exit -F arch=b64 -S open -S openat -F exit=-EPERM -k access

SEE ALSO
       auditctl(8), auditd(8).

AUTHOR
       Steve Grubb

Red Hat                            Sep 2009                    AUDIT.RULES:(7)
 

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Gedruckt am: 20.10.2017 01:40 GMT+0200 (2017-10-20T01:40:43+02:00)