audit.rules man page on Oracle

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

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

       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	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 4 rule matching lists or filters as they are some‐
       times called. They are: task, exit, user, and exclude. The task list is
       checked only during the fork or clone syscalls. It is  rarely  used  in

       The  exit  filter  is the place where all syscall and file system audit
       requests are evaluated.

       The user filter is used to filter (remove) some events  that  originate
       in  user	 space.	  By  default,	any event originating in user space is
       allowed. So, if there are some events that you do not want to see, then
       this  is	 a place where some can be removed. See auditctl(8) for fields
       that are valid.

       The exclude filter is used to exclude certain events from  being	 emit‐
       ted.  The  msgtype field is used to tell the kernel which message types
       you do not want to record. This filter can remove the event as a	 whole
       and  is not selective about any other attribute. The user and exit fil‐
       ters are better suited to selectively auditing events.

       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 at 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, exit,  user,  and	 exclude.  Their  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 than 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 in front 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 of  the  system,  you
       need  to	 look in /etc/login.defs to see where user accounts start. For
       example, if UID_MIN is  1000, then you would also  need	to  take  into
       account	that the unsigned representation of -1 is higher than 1000. So
       you would address this with the following piece of a rule:

       -F auid>=1000 -F auid!=4294967295

       These individual checks 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.

       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 --key --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‐

       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.

       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

       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 no longer available. Auditctl moved your rule
       to the exit filter so that it's 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.

       The following rule shows how to audit failed access  to	files  due  to
       permission  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

       auditctl(8), auditd(8).

       Steve Grubb

Red Hat				   Apr 2013		       AUDIT.RULES:(7)

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