Unique audit record type ranges for individual LSMs

Casey Schaufler casey at schaufler-ca.com
Wed Dec 6 18:47:43 UTC 2017

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.

> 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".

> 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?

> Tyler

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