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

Stefan Berger stefanb at linux.vnet.ibm.com
Fri May 18 11:49:45 UTC 2018


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.

     Stefan


>
> Does this help?
>
>>      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.
>>>>
>>>>https://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 at linux.vnet.ibm.com>
>>>>>> ---
>>>>>>    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 at 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
>>>
> - RGB
>
> --
> Richard Guy Briggs <rgb at 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
>



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