Unique audit record type ranges for individual LSMs

Unique audit record type ranges for individual LSMs

[Casey Schaufler]

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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Unique audit record type ranges for individual LSMs

[Steve Grubb]

On Wednesday, December 6, 2017 12:51:26 PM EST 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.
> 
> 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.
> 
> 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.

Yes, this is what I have:

#define AUDIT_AA                        1500    /* Not upstream yet */
#define AUDIT_APPARMOR_AUDIT            1501
#define AUDIT_APPARMOR_ALLOWED          1502
#define AUDIT_APPARMOR_DENIED           1503
#define AUDIT_APPARMOR_HINT             1504
#define AUDIT_APPARMOR_STATUS           1505
#define AUDIT_APPARMOR_ERROR            1506


> 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.

This seems like an erroneous comment in audit.h.


> 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

I think this commit predates the agreement on the apparmor range and a 
followup assignment in the kernel was never done.


> 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()?

This is part of the problem. I get an AVC from selinux like this:

type=AVC msg=audit(1512997597.761:271): avc:  denied  { append } for  pid=1304 
comm="mail" name="dead.letter" dev="nvme0n1p2" ino=17 
scontext=system_u:system_r:fsdaemon_t:s0 
tcontext=system_u:object_r:etc_runtime_t:s0 tclass=file permissive=0

Nowhere in this does it tell me this is from the selinux LSM. So, that means 
it is implicit in the event number. Its important for me to know what LSM sent 
this so that it can be parsed correctly. If every LSM uses the same event 
numbers as selinux, then we probably have parsing problems because they are 
being parsed like selinux events and the wording/reporting probably does not 
make sense.


> If so, does everyone agree that 1500-1599 would be acceptable for
> AppArmor to use?

In the absence of any way to determine what I'm dealing with, separating LSMs 
by event number is best.

Also, I don't get or see any events from these other LSM's. I can't reproduce 
any bugs or verify the correctness of any reports or searches. Not that I 
don't want to support other LSM's, but I need someone else to check it and 
make sure it's doing  the right thing. Patches are welcome.

-Steve
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Unique audit record type ranges for individual LSMs

[Steve Grubb]

On Wednesday, December 6, 2017 1:47:43 PM EST Casey Schaufler wrote:
> > 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 really don't know what the status is for user space support on the other 
LSMs. I couldn't tell you if the searching/reporting are broken or working 
just fine.

Additionally, there is auditctl which has very selinux specific field options 
to audit on a variety of pieces of the labels. Does this make sense for other 
LSMs? Do other LSMs have different needs? I really have no idea.

But one thing for sure...if we combine them all, I expect patches are needed 
for user space. By separating them out by event number or some identifier like 
lsm=, then we can have lsm specific fixups if necessary.

-Steve
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Unique audit record type ranges for individual LSMs

[Casey Schaufler]

On 12/11/2017 7:44 AM, Steve Grubb wrote:
> On Wednesday, December 6, 2017 1:47:43 PM EST Casey Schaufler wrote:
>>> 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 really don't know what the status is for user space support on the other 
> LSMs. I couldn't tell you if the searching/reporting are broken or working 
> just fine.

Understood. And it's only going to get worse with module stacking.

> Additionally, there is auditctl which has very selinux specific field options 
> to audit on a variety of pieces of the labels. Does this make sense for other 
> LSMs? Do other LSMs have different needs? I really have no idea.

Three of the record types are SELinux specific. Nine are netlabel, which are
not SELinux specific, or at least shouldn't be. Three are about setting state.
We could have different audit records for Smack setting netlabel maps from the
one SELinux uses, but that seems wrong.

> But one thing for sure...if we combine them all, I expect patches are needed 
> for user space. By separating them out by event number or some identifier like 
> lsm=, then we can have lsm specific fixups if necessary.

It seems to me that adding proper support for security modules
other than SELinux is going to be a project. That's true regardless
of how the messages are numbered and whether or not we have generic
messages.

> -Steve
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Unique audit record type ranges for individual LSMs

[Steve Grubb]

On Monday, December 11, 2017 3:56:35 PM EST Casey Schaufler wrote:
> On 12/11/2017 7:44 AM, Steve Grubb wrote:
> > On Wednesday, December 6, 2017 1:47:43 PM EST Casey Schaufler wrote:
> >>> 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 really don't know what the status is for user space support on the other
> > LSMs. I couldn't tell you if the searching/reporting are broken or working
> > just fine.
> 
> Understood. And it's only going to get worse with module stacking.
> 
> > Additionally, there is auditctl which has very selinux specific field
> > options to audit on a variety of pieces of the labels. Does this make
> > sense for other LSMs? Do other LSMs have different needs? I really have
> > no idea.
> 
> Three of the record types are SELinux specific. Nine are netlabel, which are
> not SELinux specific, or at least shouldn't be. Three are about setting
> state. We could have different audit records for Smack setting netlabel
> maps from the one SELinux uses, but that seems wrong.

I'd also be open to defining a block for generic messages and a couple small 
blocks (10 or so) for LSM specific events. By defining a new event type, it 
allows you to express the information specific to a LSM without having to 
conform to all other LSMs.


> > But one thing for sure...if we combine them all, I expect patches are
> > needed for user space. By separating them out by event number or some
> > identifier like lsm=, then we can have lsm specific fixups if necessary.
> 
> It seems to me that adding proper support for security modules
> other than SELinux is going to be a project. That's true regardless
> of how the messages are numbered and whether or not we have generic
> messages.

First step would be to either add lsm= to all audit events from LSM's or 
define blocks each will use. It might be best to add the lsm= field if we have 
standard events across all LSMs. Then at some future date we can start using 
that to do something smart with the extra info. But knowing which LSM emitted 
the event is important to cleaning this up.

Also...auditctl issue seems to be glossed over. Do other LSMs have auditing 
needs related to rules + labeling the LSM may do?

-Steve

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