dm: introduce audit event module for device mapper

To be able to send auditing events to user space, we introduce a
generic dm-audit module. It provides helper functions to emit audit
events through the kernel audit subsystem. We claim the
AUDIT_DM_CTRL type=1336 and AUDIT_DM_EVENT type=1337 out of the
audit event messages range in the corresponding userspace api in
'include/uapi/linux/audit.h' for those events.

AUDIT_DM_CTRL is used to provide information about creation and
destruction of device mapper targets which are triggered by user space
admin control actions.
AUDIT_DM_EVENT is used to provide information about actual errors
during operation of the mapped device, showing e.g. integrity
violations in audit log.

Following commits to device mapper targets actually will make use of
this to emit those events in relevant cases.

The audit logs look like this if executing the following simple test:

 # dd if=/dev/zero of=test.img bs=1M count=1024
 # losetup -f test.img
 # integritysetup -vD format --integrity sha256 -t 32 /dev/loop0
 # integritysetup open -D /dev/loop0 --integrity sha256 integritytest
 # integritysetup status integritytest
 # integritysetup close integritytest
 # integritysetup open -D /dev/loop0 --integrity sha256 integritytest
 # integritysetup status integritytest
 # dd if=/dev/urandom of=/dev/loop0 bs=512 count=1 seek=100000
 # dd if=/dev/mapper/integritytest of=/dev/null

-------------------------
audit.log from auditd

type=UNKNOWN[1336] msg=audit(1630425039.363:184): module=integrity
op=ctr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425039.471:185): module=integrity
op=dtr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425039.611:186): module=integrity
op=ctr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1
type=UNKNOWN[1336] msg=audit(1630425054.475:187): module=integrity
op=dtr ppid=3807 pid=3819 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425073.171:191): module=integrity
op=ctr ppid=3807 pid=3883 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425087.239:192): module=integrity
op=dtr ppid=3807 pid=3902 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1336] msg=audit(1630425093.755:193): module=integrity
op=ctr ppid=3807 pid=3906 auid=1000 uid=0 gid=0 euid=0 suid=0 fsuid=0
egid=0 sgid=0 fsgid=0 tty=pts2 ses=3 comm="integritysetup"
exe="/sbin/integritysetup" subj==unconfined dev=254:3
error_msg='success' res=1

type=UNKNOWN[1337] msg=audit(1630425112.119:194): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:195): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:196): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:197): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:198): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:199): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:200): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:201): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:202): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0
type=UNKNOWN[1337] msg=audit(1630425112.119:203): module=integrity
op=integrity-checksum dev=254:3 sector=77480 res=0

Signed-off-by: Michael Weiß <michael.weiss@aisec.fraunhofer.de>
Signed-off-by: Paul Moore <paul@paul-moore.com> # fix audit.h numbering
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

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