Re: [PATCH] audit: add containerid support for IMA-audit

From: Stefan Berger
Date: Fri May 18 2018 - 06:53:43 EST

On 05/17/2018 05:30 PM, Richard Guy Briggs wrote:
On 2018-05-17 10:18, Stefan Berger wrote:
On 03/08/2018 06:21 AM, Richard Guy Briggs wrote:
On 2018-03-05 09:24, Mimi Zohar wrote:
On Mon, 2018-03-05 at 08:50 -0500, Richard Guy Briggs wrote:
On 2018-03-05 08:43, Mimi Zohar wrote:
Hi Richard,

This patch has been compiled, but not runtime tested.
Ok, great, thank you. I assume you are offering this patch to be
included in this patchset?
Yes, thank you.

I'll have a look to see where it fits in the
IMA record. It might be better if it were an AUDIT_CONTAINER_INFO
auxiliary record, but I'll have a look at the circumstances of the
event.
I had a look at the context of this record to see if adding the contid
field to it made sense. I think the only records for which the contid
field makes sense are the two newly proposed records, AUDIT_CONTAINER
which introduces the container ID and the and AUDIT_CONTAINER_INFO which
documents the presence of the container ID in a process event (or
process-less network event). All others should use the auxiliary record
AUDIT_CONTAINER_INFO rather than include the contid field directly
itself. There are several reasons for this including record length, the
ability to filter unwanted records, the difficulty of changing the order
of or removing fields in the future.

Syscalls get this information automatically if the container ID is set
for a task via the AUDIT_CONTAINER_INFO auxiliary record. Generally a
syscall event is one that uses the task's audit_context while a
standalone event uses NULL or builds a local audit_context that is
discarded immediately after the local use.

Looking at the two cases of AUDIT_INTEGRITY_RULE record generation, it
appears that they should be split into two distinct audit record types.

The record created in ima_audit_measurement() is a syscall record that
could possibly stand on its own since the subject attributes are
present. If it remains a syscall auxiliary record it will automatically
have the AUDIT_CONTAINER_INFO record accompany it anyways. If it is
decided to detach it (which would save cpu/netlink/disk bandwidth but is
not recommended due to not wanting to throw away any other syscall
information or other involved records (PATH, CWD, etc...) then a local
audit_context would be created for the AUDIT_INTEGRITY_RULE and
AUDIT_CONTAINERID_INFO records only and immediately discarded.
What does 'detach it' mean? Does it mean we're not using
current->audit_context?
Exactly.

The record created in ima_parse_rule() is not currently a syscall record
since it is passed an audit_context of NULL and it has a very different
format that does not include any subject attributes (except subj_*=).
At first glance it appears this one should be a syscall accompanied
auxiliary record. Either way it should have an AUDIT_CONTAINER_INFO
Do you have an example (pointer) to the format for a 'syscall accompanied
auxiliary record'?
Any that uses current->audit_context (or recently proposed
audit_context() function) will be a syscall auxiliary record. Well
formed record formats are <fieldname>=<value> and named as listed:

https://github.com/linux-audit/audit-documentation/wiki/SPEC-Writing-Good-Events
https://github.com/linux-audit/audit-documentation/blob/master/specs/fields/field-dictionary.csv

auxiliary record either by being converted to a syscall auxiliary record
by using current->audit_context rather than NULL when calling
audit_log_start(), or creating a local audit_context and calling
ima_parse_rule() is invoked when setting a policy by writing it into
/sys/kernel/security/ima/policy. We unfortunately don't have the
current->audit_context in this case.
Sure you do. What process writes to that file? That's the one we care
about, unless it is somehow handed off to a queue and processed later in
a different context.

I just printk'd it again. current->audit_context is NULL in this case.


audit_log_container_info() then releasing the local context. This
version of the record has additional concerns covered here:
https://github.com/linux-audit/audit-kernel/issues/52
Following the discussion there and the concern with breaking user space, how
can we split up the AUDIT_INTEGRITY_RULE that is used in
ima_audit_measurement() and ima_parse_rule(), without 'breaking user space'?
Arguably userspace is already broken by this wildly diverging pair of
formats for the same record.

A message produced by ima_parse_rule() looks like this here:

type=INTEGRITY_RULE msg=audit(1526566213.870:305): action="dont_measure"
fsmagic="0x9fa0" res=1

in contrast to that an INTEGRITY_PCR record type:

type=INTEGRITY_PCR msg=audit(1526566235.193:334): pid=1615 uid=0 auid=0
ses=2 subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
op="invalid_pcr" cause="open_writers" comm="scp"
name="/var/log/audit/audit.log" dev="dm-0" ino=1962625 res=1

Should some of the fields from INTEGRITY_PCR also appear in INTEGRITY_RULE?
Not necessarily. There are a number of records in the PCR record that
would be redundant when connected to a syscall record, but removing them
is discouraged to avoid breaking parsers that expect them.

I don't see any need to touch the PCR record.

I wasn't going to touch the PCR record.


If so, which ones? We could probably refactor the current
integrity_audit_message() and have ima_parse_rule() call into it to get
those fields as well. I suppose adding new fields to it wouldn't be
considered breaking user space?
Changing the order of existing fields or inserting fields could break
stuff and is strongly discouraged without a good reason, but appending
fields is usually the right way to add information.

There are exceptions, and in this case, I'd pick the "more standard" of
the formats for AUDIT_INTEGRITY_RULE (ima_audit_measurement?) and stick
with that, abandoning the other format, renaming the less standard
version of the record (ima_parse_rule?) and perhpas adopting that
abandonned format for the new record type while using
current->audit_context.

Since current->audit_context is NULL I built on your patch, but I am not sure whether it is justifyable to use that before your container id series is applied.

This is what ima_parse_rule() produces now after having it call audit_log_task_info() as well and by introducing 1806 for ima_parse_rule() only ( https://lkml.org/lkml/2018/5/11/386 ):

type=UNKNOWN[1806] msg=audit(1526643702.328:304): action="dont_measure" fsmagic="0x9fa0" res=1 ppid=1563 pid=1595 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=tty2 ses=2 comm="cat" exe="/usr/bin/cat" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023

[before: type=INTEGRITY_RULE msg=audit(1526566213.870:305): action="dont_measure" fsmagic="0x9fa0" res=1]

For comparison the INTEGRITY_RULE:

type=INTEGRITY_RULE msg=audit(1526642504.074:331): file="/usr/bin/ssh" hash="sha256:4abc2558424b9ca61c34af43169d9b9e174d7825bf60c9c76be377549081db5b" ppid=1623 pid=1624 auid=0 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=tty2 ses=2 comm="scp" exe="/usr/bin/scp" subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023


1806 would be in sync with INTEGRITY_RULE now for process related info. If this looks good, I'll remove the dependency on your local context creation and post the series.

The justification for the change is that the INTEGRITY_RULE, as produced by ima_parse_rule(), is broken.

ÂÂÂ Stefan



Does this help?

ÂÂÂ Stefan

Can you briefly describe the circumstances under which these two
different identically-numbered records are produced as a first step
towards splitting them into two distict records?

The four AUDIT_INTEGRITY _METADATA, _PCR, _DATA and _STATUS records
appear to be already properly covered for AUDIT_CONTAINER_INFO records
by being syscall auxiliary records. The AUDIT_INTEGRITY_HASH record
appears to be unused.

Can you suggest a procedure to test it?
Like IMA-measurement and IMA-appraisal, IMA-audit is enabled based on
policy. The example IMA policy, below, includes IMA-audit messages for
files executed. 'cat' the policy to /sys/kernel/security/ima/policy.

/etc/ima/ima-policy:
audit func=BPRM_CHECK

There's a FireEye blog titled "Extending Linux Executable Logging With
The Integrity Measurement Architecture"* that explains how to augment
their existing system security analytics with file hashes.

*Âhttps://www.fireeye.com/blog/threat-research/2016/11/extending_linux
_exec.html


Mimi

If the containerid is defined, include it in the IMA-audit record.

Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx>
---
security/integrity/ima/ima_api.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/security/integrity/ima/ima_api.c b/security/integrity/ima/ima_api.c
index 33b4458cdbef..41d29a06f28f 100644
--- a/security/integrity/ima/ima_api.c
+++ b/security/integrity/ima/ima_api.c
@@ -335,6 +335,9 @@ void ima_audit_measurement(struct integrity_iint_cache *iint,
audit_log_untrustedstring(ab, algo_hash);
audit_log_task_info(ab, current);
+ if (audit_containerid_set(current))
+ audit_log_format(ab, " contid=%llu",
+ audit_get_containerid(current));
audit_log_end(ab);
iint->flags |= IMA_AUDITED;
--
2.7.5

- RGB
- 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

- 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