Re: [PATCH 8/8] ima: Differentiate auditing policy rules from "audit" actions

Stefan Berger
2018-06-01T20:00:47Z

On 05/30/2018 07:34 PM, Richard Guy Briggs wrote:
> On 2018-05-30 17:38, Stefan Berger wrote:
>> On 05/30/2018 05:22 PM, Paul Moore wrote:
>>> On Wed, May 30, 2018 at 9:08 AM, Stefan Berger
>>> <stefanb@linux.vnet.ibm.com> wrote:
>>>> On 05/30/2018 08:49 AM, Richard Guy Briggs wrote:
>>>>> On 2018-05-24 16:11, Stefan Berger wrote:
>>>>>> The AUDIT_INTEGRITY_RULE is used for auditing IMA policy rules and
>>>>>> the IMA "audit" policy action. This patch defines
>>>>>> AUDIT_INTEGRITY_POLICY_RULE to reflect the IMA policy rules.
>>>>>>
>>>>>> With this change we now call integrity_audit_msg_common() to get
>>>>>> common integrity auditing fields. This now produces the following
>>>>>> record when parsing an IMA policy rule:
>>>>>>
>>>>>> type=UNKNOWN[1806] msg=audit(1527004216.690:311): action=dont_measure \
>>>>>> fsmagic=0x9fa0 pid=1613 uid=0 auid=0 ses=2 \
>>>>>> subj=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023 \
>>>>>> op=policy_update cause=parse_rule comm="echo" exe="/usr/bin/echo" \
>>>>>> tty=tty2 res=1
>>>>>>
>>>>>> Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
>>>>>> ---
>>>>>> include/uapi/linux/audit.h | 3 ++-
>>>>>> security/integrity/ima/ima_policy.c | 5 +++--
>>>>>> 2 files changed, 5 insertions(+), 3 deletions(-)
>>>>>>
>>>>>> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
>>>>>> index 4e61a9e05132..776e0abd35cf 100644
>>>>>> --- a/include/uapi/linux/audit.h
>>>>>> +++ b/include/uapi/linux/audit.h
>>>>>> @@ -146,7 +146,8 @@
>>>>>> #define AUDIT_INTEGRITY_STATUS 1802 /* Integrity enable
>>>>>> status */
>>>>>> #define AUDIT_INTEGRITY_HASH 1803 /* Integrity HASH type */
>>>>>> #define AUDIT_INTEGRITY_PCR 1804 /* PCR invalidation msgs */
>>>>>> -#define AUDIT_INTEGRITY_RULE 1805 /* policy rule */
>>>>>> +#define AUDIT_INTEGRITY_RULE 1805 /* IMA "audit" action policy
>>>>>> msgs */
>>>>>> +#define AUDIT_INTEGRITY_POLICY_RULE 1806 /* IMA policy rules */
>>>>>> #define AUDIT_KERNEL 2000 /* Asynchronous audit
>>>>>> record. NOT A REQUEST. */
>>>>>> diff --git a/security/integrity/ima/ima_policy.c
>>>>>> b/security/integrity/ima/ima_policy.c
>>>>>> index 3aed25a7178a..a8ae47a386b4 100644
>>>>>> --- a/security/integrity/ima/ima_policy.c
>>>>>> +++ b/security/integrity/ima/ima_policy.c
>>>>>> @@ -634,7 +634,7 @@ static int ima_parse_rule(char *rule, struct
>>>>>> ima_rule_entry *entry)
>>>>>> int result = 0;
>>>>>> ab = integrity_audit_log_start(NULL, GFP_KERNEL,
>>>>>> - AUDIT_INTEGRITY_RULE);
>>>>>> + AUDIT_INTEGRITY_POLICY_RULE);
>>>>> Is it possible to connect this record to a syscall by replacing the
>>>>> first parameter (NULL) by current->context?
>>> We're likely going to need to "associate" this record (audit speak for
>>> making the first parameter non-NULL) with others for the audit
>>> container ID work. If you do it now, Richard's patches will likely
>>> get a few lines smaller and that will surely make him a bit happier :)
>> Richard is also introducing a local context that we can then create and use
>> instead of the NULL. Can we not use that then?
> That is for records for which there is no syscall or user associated.
>
> In fact there is another recent change that would be better to use than
> current->audit_context, which is the function audit_context().
> See commit cdfb6b3 ("audit: use inline function to get audit context").
>
>> Steven seems to say: "We don't want to add syscall records to everything.
>> That messes up schemas and existing code. The integrity events are 1 record
>> in size and should stay that way. This saves disk space and improves
>> readability."
>>
>>>> We would have to fix current->context in this case since it is NULL. We get
>>>> to this location by root cat'ing a policy or writing a policy filename into
>>>> /sys/kernel/security/ima/policy.
>>> Perhaps I'm missing something, but current in this case should point
>>> to the process which is writing to the policy file, yes?
>> Yes, but current->context is NULL for some reason.
> Is it always this way? If it isn't, which it should not be, we should
> find out why. Well, we should find out why this is NULL anyways, since
> it shouldn't be.

When someone writes a policy for IMA into securityfs, it's always NULL.
There's another location where IMA uses the current->audit_context, and
that's here:

https://elixir.bootlin.com/linux/latest/source/security/integrity/ima/ima_api.c#L323

At this location we sometimes see a (background) process with an
audit_context but in the majority of cases it's current->audit_context
is NULL. Starting a process as root or also non-root user, with the
appropriate IMA audit policy rules set, we always see a NULL
audit_context here.

>
> - 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
>