Unique audit record type ranges for individual LSMs

[Tyler Hicks]

On 12/06/2017 12:47 PM, Casey Schaufler wrote:
> On 12/6/2017 9:51 AM, Tyler Hicks wrote:
>> Hello - The AppArmor project would like for AppArmor audit records to be
>> supported by the audit-userspace tools, such as ausearch, but it
>> requires some coordination between the linux-security-module and
>> linux-audit lists. This was raised as a feature request years ago in
>> Ubuntu and more recently in Debian:
>>
>>   https://launchpad.net/bugs/1117804
>>   https://bugs.debian.org/872726
>>
>> The quick summary of the problem at hand is that the audit-userspace
>> project requires that each LSM use a unique record type range for audit
>> records while the kernel's common_lsm_audit() function uses the same
>> record type (1400) for all records. SELinux, AppArmor, and SMACK are all
>> using common_lsm_audit() today and, therefore, the 1400-1499 range.
> 
> My, but this is a rat's nest, isn't it? The constants, such as AUDIT_MAC_STATUS,
> look as if they are intended to be generic. But the comment says the range is
> for SELinux. Some of the events, including AUDIT_MAC_MAP_ADD *are* generic, in
> that they are from the netlbl subsystem. But some, AUDIT_AVC being paramount,
> are indeed SELinux specific.

It is a rat's nest, which is why the Ubuntu bug above has lingered for
so long.

Good point regarding AUDIT_MAC_MAP_ADD being generic.

> 
>> While it will be potentially painful to switch, the AppArmor project is
>> considering to use a unique range in order for audit-userspace to
>> support AppArmor audit records. IMHO, SMACK would be free to continue
>> using 1400-1499 as long as they don't need audit-userspace support and
>> SELinux would continue using 1400-1499.
> 
> Aside from the comment that says 1400-1499 are for SELinux, and the three
> events (1400-1402) that are SELinux specific, the events really are general.
> Why not add the AppArmor specifics to the 1400 range? Give them a generic
> sounding name and you'll achieve consistency. Change the comment to say
> "Security Module use" instead of "SELinux use".

I would be alright with this solution. We could even claim 1400-1599 or
even 1400-1699 for "Security Module use" if we thought 100 record types
may not be enough in the future.

I could see how there may be a desire for each LSM to have their own
blocks of 100 where they can assign record types freely without
coordination with LSM maintainers but I don't feel like new record types
come around often enough for this to matter much.

> 
>> Steve Grubb previously told me that he intends 1500-1599 to be used by
>> AppArmor:
>>
>>   https://www.redhat.com/archives/linux-audit/2014-May/msg00119.html
>>
>>
>> John Johansen tells me that AppArmor previously used the 1500-1599 range
>> before AppArmor was upstreamed.
>>
>> There's a conflicting comment in the kernel stating that 1500-1599 is to
>> by used by kernel LSPP events. As far as I can tell, there were never
>> any kernel LSPP events that used the range. Steve is the one that added
>> that comment so I think it is a safe range for AppArmor to use:
>>
>>   https://git.kernel.org/linus/90d526c074ae5db484388da56c399acf892b6c17
>>
>> Considering audit-userspace's stance, does the LSM community agree that
>> common_lsm_audit() should be modified to accept an audit record type
>> parameter to pass on to audit_log_start()?
>>
>> If so, does everyone agree that 1500-1599 would be acceptable for
>> AppArmor to use?
> 
> Why not change the comment and continue to use the 1400 range, adding
> events as necessary?

I don't have any problems with that but I'd like Steve Grubb to weigh in
on it.

Tyler

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