Provided by: auditd_3.0.7-1ubuntu1_amd64 bug


       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 syntax 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 varieties: 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 interested 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  recursive  directory watch will stop if there is a mount point below the parent
       directory. There is an option to make the mounted subdirectory equivalent by  using  a  -q

   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 sometimes called. They
       are: task, exit, user, exclude, and filesystem. 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

       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 emitted. 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  selectively
       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, exclude, and filesystem. 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 system uses the number
       -1 to indicate that a loginuid is not set. This means that when it's printed out, it looks
       like  4294967295.  But  when  you write rules, you can use either "unset" which is easy to
       remember, or -1, or 4294967295. They are all equivalent. 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 500. So you
       would address this with the following piece of a rule:

       -F auid>=1000 -F auid!=unset

       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 periodically 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 system. 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 -S openat2 -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 unauthorized 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  matching  event  id  and
       interpret the numeric values into human readable values.

       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 associated 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 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,

       -a always,exit -S openat -k access

       would be rewritten as

       -a always,exit -F arch=b32 -S openat -k access
       -a 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 filter, 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 -S openat2 -F exit=-EACCES -k access
       -a always,exit -F arch=b32 -S open -S openat -S openat2 -F exit=-EPERM -k access
       -a always,exit -F arch=b64 -S open -S openat -S openat2 -F exit=-EACCES -k access
       -a always,exit -F arch=b64 -S open -S openat -S openat2 -F exit=-EPERM -k access


       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 compliance 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


       auditctl(8), auditd(8).


       Steve Grubb