audit.rules(inc) - phpMan

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 a watch 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  watch
       rules generally 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
       Watches  can  also  be created using the syscall format described below
       which allow for greater flexibility and options.  Using  syscall  rules
       you  can  choose between path and dir which is against a specific inode
       or directory tree respectively. It should also be noted that the recur-
       sive directory watch will stop if there is a mount point below the par-
       ent directory. There is an option  to  make  the  mounted  subdirectory
       equivalent by using a -q rule.

   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
       practice.
       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 and a number of subject attribute fields can be 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 filters are better suited to  selec-
       tively  auditing  events.   The  action  is  ignored  for  this filter,
       defaulting to "never".
       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  it's
       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  it's  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  500, then you would also need to take  into
       account  that  the unsigned 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 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.

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 --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 -S openat -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 openat -k access
       would be rewritten as
       -always,exit -F arch=b32 -S openat -k access
       -always,exit -F arch=b64 -S openat -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.

EXAMPLES
       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

HARD WIRED EVENTS
       If  auditing  is enabled, then you can get any event that is not caused
       by syscall or file watch  rules  (because  you  don't  have  any  rules
       loaded). So, that means, any event from 1100-1299, 1326, 1328, 1331 and
       higher can be emitted. The reason that there are  a  number  of  events
       that  are  hardwired is because they are required by regulatory compli-
       ance and  are  sent  automatically  as  a  convenience.  (For  example,
       logon/logoff  is  a  mandatory  event in all security guidance.) If you
       don't want this, you can use the exclude filter to drop events that you
       do not want.
       -a always,exclude -F msgtype=CRED_REFR

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

AUTHOR
       Steve Grubb

Red Hat                            Jan 2019                    AUDIT.RULES:(7)