audit.rules(7) — Linux manual page

NAME | DESCRIPTION | NOTES | TROUBLESHOOTING | EXAMPLES | HARD WIRED EVENTS | SEE ALSO | AUTHOR | COLOPHON

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

NAME         top

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

DESCRIPTION         top

       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
       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
       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
       sometimes 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
       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, 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
       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.

NOTES         top

       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 -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.

TROUBLESHOOTING         top

       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.

EXAMPLES         top

       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         top

       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

SEE ALSO         top

       auditctl(8), auditd(8).

AUTHOR         top

       Steve Grubb

COLOPHON         top

       This page is part of the audit (Linux Audit) project.
       Information about the project can be found at 
       ⟨http://people.redhat.com/sgrubb/audit/⟩.  If you have a bug
       report for this manual page, send it to linux-audit@redhat.com.
       This page was obtained from the project's upstream Git repository
       ⟨https://github.com/linux-audit/audit-userspace.git⟩ on
       2021-04-01.  (At that time, the date of the most recent commit
       that was found in the repository was 2021-03-29.)  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to man-pages@man7.org

Red Hat                         Jan 2019                 AUDIT.RULES:(7)

Pages that refer to this page: auditctl(8)auditd(8)augenrules(8)