[v2,0/3] dm: audit event logging

Message

Michael Weiß Aug. 14, 2021, 6:33 p.m. UTC

dm integrity and also stacked dm crypt devices track integrity
violations internally. Thus, integrity violations could be polled
from user space, e.g., by 'integritysetup status'.

>From an auditing perspective, we only could see that there were
a number of integrity violations, but not when and where the
violation exactly was taking place. The current error log to
the kernel ring buffer, contains those information, time stamp and
sector on device. However, for auditing the audit subsystem provides
a separate logging mechanism which meets certain criteria for secure
audit logging.

With this small series we make use of the kernel audit framework
and extend the dm driver to log audit events in case of such
integrity violations. Further, we also log construction and
destruction of the device mappings.

We focus on dm-integrity and stacked dm-crypt devices for now.
However, the helper functions to log audit messages should be
applicable to dm verity too.

The first patch introduce generic audit wrapper functions.
The second patch makes use of the audit wrapper functions in the
dm-integrity.c.
The third patch uses the wrapper functions in dm-crypt.c.

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(1628692862.187:409): module=integrity dev=254:3 op=ctr res=1
type=UNKNOWN[1336] msg=audit(1628692862.443:410): module=integrity dev=254:3 op=dtr res=1
type=UNKNOWN[1336] msg=audit(1628692862.543:411): module=integrity dev=254:3 op=ctr res=1
type=UNKNOWN[1336] msg=audit(1628692877.943:412): module=integrity dev=254:3 op=dtr res=1

type=UNKNOWN[1336] msg=audit(1628692887.287:413): module=integrity dev=254:3 op=ctr res=1

type=UNKNOWN[1336] msg=audit(1628692925.156:417): module=integrity dev=254:3 op=dtr res=1

type=UNKNOWN[1336] msg=audit(1628692930.720:418): module=integrity dev=254:3 op=ctr res=1

type=UNKNOWN[1336] msg=audit(1628692989.344:419): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:420): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:421): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:422): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:423): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:424): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:425): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:426): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:427): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0
type=UNKNOWN[1336] msg=audit(1628692989.348:428): module=integrity dev=254:3 op=integrity-checksum sector=77480 res=0

v2 Changes:
- Fixed compile errors if CONFIG_DM_AUDIT is not set
- Fixed formatting and typos as suggested by Casey

Michael Weiß (3):
  dm: introduce audit event module for device mapper
  dm integrity: log audit events for dm-integrity target
  dm crypt: log aead integrity violations to audit subsystem

 drivers/md/Kconfig         | 10 +++++++
 drivers/md/Makefile        |  4 +++
 drivers/md/dm-audit.c      | 59 ++++++++++++++++++++++++++++++++++++++
 drivers/md/dm-audit.h      | 33 +++++++++++++++++++++
 drivers/md/dm-crypt.c      | 22 +++++++++++---
 drivers/md/dm-integrity.c  | 25 +++++++++++++---
 include/uapi/linux/audit.h |  1 +
 7 files changed, 146 insertions(+), 8 deletions(-)
 create mode 100644 drivers/md/dm-audit.c
 create mode 100644 drivers/md/dm-audit.h