Re: [PATCH v4 0/3] dm: audit event logging

["Weiß, Michael" <michael.weiss@aisec.fraunhofer.de>]

On Tue, 2021-09-07 at 20:59 -0400, Richard Guy Briggs wrote:
> On 2021-09-04 11:59, Michael Weiß wrote:
> > 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(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
> 
> Are these isolated records, or are they accompanied by a type=SYSCALL
> record in your logs?

You are right the dm_audit_log_{ctr,dtr} functions produce type=AUDIT_DM_CTRL
accompanied by a
type=SYSCALL. This was a mistake by me. I grepped
the audit log with 'grep -e "133[6-7]"' during my
tests, thus I have
missed that. I will remove the audit_log_task_info() call in the
internal dm_audit_log_ti() function
for type=AUDIT_DM_CTRL.

dm_audit_log_target and dm_audit_log_bio are using type=AUDIT_DM_EVENT,
These are isolated events since they are not triggert in user context. 

> 
> The reason I ask is that audit_log_task_info() is included in three of
> the calling methods (dm_audit_log_{target,ctr,dtr}) which use a
> combination of AUDIT_DM_CTRL/AUDIT_DM_EVENT type while the fourth
> (dm_audit_log_bio) also uses one of the types above but does not include
> audit_log_task_info().  If all these records are accompanied by SYSCALL
> records, then the task info would be redundant (and might even conflict
> if there's a bug).  Another minor oddity is the double "=" for the subj
> field, which doesn't appear to be a bug in your code, but still puzzling.

In the test setup, I had Apparmor enabled and set as default security module.
This behavior occurs in any audit_log message.
Seems that this is coming from the label handling there. Having a quick look
at the code there is that they use '=' in the label to provide a root view as
part of their policy virtualization. The corresponding commit is sitting
there since 2017: "26b7899510ae243e392960704ebdba52d05fbb13"

> 
> Are those last 10 records expected to be identical other than event
> serial number?

Yes, because the access to the corrupt sector is made 10 times.
This reflects exactly the same behavior without the audit logging, in the 
kernel debug log.

> 
> > v4 Changes:
> > - Added comments on intended use of wrapper functions in dm-audit.h
> > - dm_audit_log_bio(): Fixed missing '=' as spotted by Paul
> > - dm_audit_log_ti(): Handle wrong audit_type as suggested by Paul
> > 
> > v3 Changes:
> > - Use of two audit event types AUDIT_DM_EVENT und AUDIT_DM_CTRL
> > - Additionaly use audit_log_task_info in case of AUDIT_DM_CTRL messages
> > - Provide consistent fields per message type as suggested by Paul
> > - Added sample events to commit message of [1/3] as suggested by Paul
> > - Rebased on v5.14
> > 
> > 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      | 84 ++++++++++++++++++++++++++++++++++++++
> >  drivers/md/dm-audit.h      | 66 ++++++++++++++++++++++++++++++
> >  drivers/md/dm-crypt.c      | 22 ++++++++--
> >  drivers/md/dm-integrity.c  | 25 ++++++++++--
> >  include/uapi/linux/audit.h |  2 +
> >  7 files changed, 205 insertions(+), 8 deletions(-)
> >  create mode 100644 drivers/md/dm-audit.c
> >  create mode 100644 drivers/md/dm-audit.h
> > 
> > -- 
> > 2.20.1
> > 
> > --
> > Linux-audit mailing list
> > Linux-audit@redhat.com
> > https://listman.redhat.com/mailman/listinfo/linux-audit
> 
> - RGB
> 
> --
> Richard Guy Briggs <rgb@redhat.com>
> Sr. S/W Engineer, Kernel Security, Base Operating Systems
> Remote, Ottawa, Red Hat Canada
> IRC: rgb, SunRaycer
> Voice: +1.647.777.2635, Internal: (81) 32635
> 

Thanks,
Michael

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