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

From: Richard Guy Briggs
Date: Wed Sep 08 2021 - 09:16:45 EST

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On 2021-09-08 08:26, Weiß, Michael wrote:
> 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.

(To get the whole events, use "ausearch ... -m 1336,1337 ...".)

> 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.

Ok, so it sounds like those events *should* have task_info in their
record format since they are not accompanied by SYSCALL records that
already contain that information. So it appears that
audit_log_task_info() should be moved from the type=AUDIT_DM_CTRL case
to the type=AUDIT_DM_EVENT case.

> > 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"

Interesting... Thanks for tracking down that cause. I don't know how
much pain that will cause the userspace parsing tools. I've added Steve
Grubb to the Cc: to get his input, but this should not derail this patch
set.

This has parallels to this previously reported issue with ima/integrity:
https://github.com/linux-audit/audit-kernel/issues/113

> > 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.

Is there any other distinguishing information for that event other than
audit log serial number that would be useful to add? (It doesn't sound
like it.)

> > > 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@xxxxxxxxxx
> > > https://listman.redhat.com/mailman/listinfo/linux-audit
> >
> > - RGB
> >
> > --
> > Richard Guy Briggs <rgb@xxxxxxxxxx>
> > 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

- RGB

--
Richard Guy Briggs <rgb@xxxxxxxxxx>
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

Next message: Christian Borntraeger: "Re: [PATCH v3 2/3] s390x: KVM: Implementation of Multiprocessor Topology-Change-Report"
Previous message: Nicolas Dufresne: "Re: [PATCH v8 03/15] media:Add v4l2 buf flag codec data."
In reply to: Weiß, Michael: "Re: [PATCH v4 0/3] dm: audit event logging"
Next in thread: Steve Grubb: "Re: [PATCH v4 0/3] dm: audit event logging"
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