Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

[Casey Schaufler]

I'm looking at the audit userspace implications of adding two
new kernel audit records. AUDIT_MAC_TASK_CONTEXTS and
AUDIT_MAC_OBJ_CONTEXTS are used when there are multiple security
modules with a "security context" active on the system. This
design has been discussed here at length. The records will look
like:

	AUDIT_MAC_TASK_CONTEXTS
	subj_<lsmname>=value
	subj_<lsmname>=value
	...

Looking at the audit user-space code I see several things
that have me concerned. The first is the use of WITH_APPARMOR.
Going forward what behavior would we want if subj_apparmor=something
shows up on a system that has not got WITH_APPARMOR defined?
The code is inconsistent in that it does not use WITH_SELINUX,
but that's hardly a surprise given its origins. There is also no
WITH_SMACK, but that's unlikely to be an issue since Smack's use
of audit is very much like SELinux's. The question is what to
do about filtering when subj=foo is specified. I suggest that if
any of subj_selinux, subj_smack or subj_something is "foo", it is
a match. But the SELinux components of a label (level, user, ...)
are also available for filtering. If someone wrote a simple Bell &
LaPadula LSM filtering by some of those fields could be useful
there, too.

I would like guidance on whether I ought to go the route of
more extensive use of WITH_APPARMOR (and WITH_SMACK, WITH_MUMBLE)
or take the path of greater generalization. Or, whether I should
treat each case individually and give it my best whack.

Thank you.



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Re: Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

[Steve Grubb]

Hello,

On Monday, June 14, 2021 3:34:33 PM EDT Casey Schaufler wrote:
> I'm looking at the audit userspace implications of adding two
> new kernel audit records. AUDIT_MAC_TASK_CONTEXTS and
> AUDIT_MAC_OBJ_CONTEXTS are used when there are multiple security
> modules with a "security context" active on the system. This
> design has been discussed here at length. The records will look
> like:
> 
> 	AUDIT_MAC_TASK_CONTEXTS
> 	subj_<lsmname>=value
> 	subj_<lsmname>=value
> 	...
> 
> Looking at the audit user-space code I see several things
> that have me concerned. The first is the use of WITH_APPARMOR.
> Going forward what behavior would we want if subj_apparmor=something
> shows up on a system that has not got WITH_APPARMOR defined?

I think it should be ignored.

> The code is inconsistent in that it does not use WITH_SELINUX,
> but that's hardly a surprise given its origins. There is also no
> WITH_SMACK, but that's unlikely to be an issue since Smack's use
> of audit is very much like SELinux's.

We can add those WITH_* if you like.

> The question is what to
> do about filtering when subj=foo is specified. I suggest that if
> any of subj_selinux, subj_smack or subj_something is "foo", it is
> a match.

I think that's how we already treat things. There is a linked list for AVC's 
and we match on any of.

> But the SELinux components of a label (level, user, ...)
> are also available for filtering. If someone wrote a simple Bell &
> LaPadula LSM filtering by some of those fields could be useful
> there, too.
> 
> I would like guidance on whether I ought to go the route of
> more extensive use of WITH_APPARMOR (and WITH_SMACK, WITH_MUMBLE)
> or take the path of greater generalization. Or, whether I should
> treat each case individually and give it my best whack.

To be honest, I have no idea how well the audit system works with any MAC 
system except SE Linux. I don't really know if its doing the right thing. 
Ausearch and report share a parser. It is time sensitive. I usually test it 
on 4 or 5 Gb of logs. We also have the ausearch-test program which can be 
used to test any changes to the parser.

http://people.redhat.com/sgrubb/audit/ausearch-test-0.6.tar.gz

Once that is squared away, there is the auparse library. It has a table that 
classifies a field name into what it is for interpretation purposes. You will 
find a #ifdef WITH_APPARMOR. I don't know if that table is complete or if it 
needs to be extended for any other MAC system.

That then leads to the auparse normalizer. I don't know if we need to make 
any changes there. You can trigger its code with ausearch --format csv or --
format text.

Also, we have some size limits in user space. How big can an event record be 
if the file is MAX_PATH name length and it has a space in its name or 
directory and each context is it's maximum size? We may need to think about 
how this might change the whole userspace ecosystem's size definition, 
MAX_AUDIT_MESSAGE_LENGTH, since this is part of the ABI. And the kernel also 
has AUDIT_MESSAGE_TEXT_MAX. What would you get with:

# /usr/sbin/auditctl -m `perl -e 'print "A"x8880'`

And last...what about auditctl? Is the syscall filter going to allow filtering 
on these other subject/object components?

-Steve


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Re: Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

[Casey Schaufler]

On 6/14/2021 2:13 PM, Steve Grubb wrote:
> Hello,
>
> On Monday, June 14, 2021 3:34:33 PM EDT Casey Schaufler wrote:
>> I'm looking at the audit userspace implications of adding two
>> new kernel audit records. AUDIT_MAC_TASK_CONTEXTS and
>> AUDIT_MAC_OBJ_CONTEXTS are used when there are multiple security
>> modules with a "security context" active on the system. This
>> design has been discussed here at length. The records will look
>> like:
>>
>> 	AUDIT_MAC_TASK_CONTEXTS
>> 	subj_<lsmname>=value
>> 	subj_<lsmname>=value
>> 	...
>>
>> Looking at the audit user-space code I see several things
>> that have me concerned. The first is the use of WITH_APPARMOR.
>> Going forward what behavior would we want if subj_apparmor=something
>> shows up on a system that has not got WITH_APPARMOR defined?
> I think it should be ignored.
>
>> The code is inconsistent in that it does not use WITH_SELINUX,
>> but that's hardly a surprise given its origins. There is also no
>> WITH_SMACK, but that's unlikely to be an issue since Smack's use
>> of audit is very much like SELinux's.
> We can add those WITH_* if you like.
>
>> The question is what to
>> do about filtering when subj=foo is specified. I suggest that if
>> any of subj_selinux, subj_smack or subj_something is "foo", it is
>> a match.
> I think that's how we already treat things. There is a linked list for AVC's 
> and we match on any of.
>
>> But the SELinux components of a label (level, user, ...)
>> are also available for filtering. If someone wrote a simple Bell &
>> LaPadula LSM filtering by some of those fields could be useful
>> there, too.
>>
>> I would like guidance on whether I ought to go the route of
>> more extensive use of WITH_APPARMOR (and WITH_SMACK, WITH_MUMBLE)
>> or take the path of greater generalization. Or, whether I should
>> treat each case individually and give it my best whack.
> To be honest, I have no idea how well the audit system works with any MAC 
> system except SE Linux.

Understood. Part of what I'm looking at is ensuring that as multiple
concurrent LSMs come in that the audit user-space isn't mucked up.
ausearch has these options:

	-o,--object <SE Linux Object context>
	-se,--context <SE Linux context>
	-su,--subject <SE Linux context>

Without multiple LSMs we can easily ignore "SE Linux" in these
options and use whatever kind of "context" is available. If I
have SELinux and AppArmor, the implication is that you can't
search on AppArmor information. Should we be adding

	-aa,--apparmorcontext <AppArmor context>
	-as,--apparmorsubject <AppArmor subject context>

or should we change -se to look at all "contexts", and change
the description to reflect that? Basicaly, I'm asking whether you'd
rather add options for other LSMs or remove descriptions that
specify SELinux.

>  I don't really know if its doing the right thing. 
> Ausearch and report share a parser. It is time sensitive. I usually test it 
> on 4 or 5 Gb of logs. We also have the ausearch-test program which can be 
> used to test any changes to the parser.
>
> http://people.redhat.com/sgrubb/audit/ausearch-test-0.6.tar.gz
>
> Once that is squared away, there is the auparse library. It has a table that 
> classifies a field name into what it is for interpretation purposes. You will 
> find a #ifdef WITH_APPARMOR. I don't know if that table is complete or if it 
> needs to be extended for any other MAC system.
>
> That then leads to the auparse normalizer. I don't know if we need to make 
> any changes there. You can trigger its code with ausearch --format csv or --
> format text.
>
> Also, we have some size limits in user space. How big can an event record be 
> if the file is MAX_PATH name length and it has a space in its name or 
> directory and each context is it's maximum size? We may need to think about 
> how this might change the whole userspace ecosystem's size definition, 
> MAX_AUDIT_MESSAGE_LENGTH, since this is part of the ABI. And the kernel also 
> has AUDIT_MESSAGE_TEXT_MAX. What would you get with:
>
> # /usr/sbin/auditctl -m `perl -e 'print "A"x8880'`
>
> And last...what about auditctl? Is the syscall filter going to allow filtering 
> on these other subject/object components?
>
> -Steve
>
>


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Re: Adding support for MAC_TASK_CONTEXTS and MAC_OBJ_CONTEXTS to userspace.

[Steve Grubb]

On Tuesday, June 15, 2021 1:01:18 PM EDT Casey Schaufler wrote:
> On 6/14/2021 2:13 PM, Steve Grubb wrote:
> > Hello,
> > 
> > On Monday, June 14, 2021 3:34:33 PM EDT Casey Schaufler wrote:
> >> I'm looking at the audit userspace implications of adding two
> >> new kernel audit records. AUDIT_MAC_TASK_CONTEXTS and
> >> AUDIT_MAC_OBJ_CONTEXTS are used when there are multiple security
> >> modules with a "security context" active on the system. This
> >> design has been discussed here at length. The records will look
> >> 
> >> like:
> >> 	AUDIT_MAC_TASK_CONTEXTS
> >> 	subj_<lsmname>=value
> >> 	subj_<lsmname>=value
> >> 	...
> >> 
> >> Looking at the audit user-space code I see several things
> >> that have me concerned. The first is the use of WITH_APPARMOR.
> >> Going forward what behavior would we want if subj_apparmor=something
> >> shows up on a system that has not got WITH_APPARMOR defined?
> > 
> > I think it should be ignored.
> > 
> >> The code is inconsistent in that it does not use WITH_SELINUX,
> >> but that's hardly a surprise given its origins. There is also no
> >> WITH_SMACK, but that's unlikely to be an issue since Smack's use
> >> of audit is very much like SELinux's.
> > 
> > We can add those WITH_* if you like.
> > 
> >> The question is what to
> >> do about filtering when subj=foo is specified. I suggest that if
> >> any of subj_selinux, subj_smack or subj_something is "foo", it is
> >> a match.
> > 
> > I think that's how we already treat things. There is a linked list for
> > AVC's and we match on any of.
> > 
> >> But the SELinux components of a label (level, user, ...)
> >> are also available for filtering. If someone wrote a simple Bell &
> >> LaPadula LSM filtering by some of those fields could be useful
> >> there, too.
> >> 
> >> I would like guidance on whether I ought to go the route of
> >> more extensive use of WITH_APPARMOR (and WITH_SMACK, WITH_MUMBLE)
> >> or take the path of greater generalization. Or, whether I should
> >> treat each case individually and give it my best whack.
> > 
> > To be honest, I have no idea how well the audit system works with any MAC
> > system except SE Linux.
> 
> Understood. Part of what I'm looking at is ensuring that as multiple
> concurrent LSMs come in that the audit user-space isn't mucked up.
> ausearch has these options:
> 
> 	-o,--object <SE Linux Object context>
> 	-se,--context <SE Linux context>
> 	-su,--subject <SE Linux context>
> 
> Without multiple LSMs we can easily ignore "SE Linux" in these
> options and use whatever kind of "context" is available. If I
> have SELinux and AppArmor, the implication is that you can't
> search on AppArmor information. Should we be adding
> 
> 	-aa,--apparmorcontext <AppArmor context>
> 	-as,--apparmorsubject <AppArmor subject context>
> 
> or should we change -se to look at all "contexts", and change
> the description to reflect that? Basicaly, I'm asking whether you'd
> rather add options for other LSMs or remove descriptions that
> specify SELinux.

I'd say any/all contexts available by default. Then we can maybe make a 
restriction to specific LSM's later.

-Steve

> >  I don't really know if its doing the right thing.
> > 
> > Ausearch and report share a parser. It is time sensitive. I usually test
> > it on 4 or 5 Gb of logs. We also have the ausearch-test program which
> > can be used to test any changes to the parser.
> > 
> > http://people.redhat.com/sgrubb/audit/ausearch-test-0.6.tar.gz
> > 
> > Once that is squared away, there is the auparse library. It has a table
> > that classifies a field name into what it is for interpretation
> > purposes. You will find a #ifdef WITH_APPARMOR. I don't know if that
> > table is complete or if it needs to be extended for any other MAC
> > system.
> > 
> > That then leads to the auparse normalizer. I don't know if we need to
> > make
> > any changes there. You can trigger its code with ausearch --format csv or
> > -- format text.
> > 
> > Also, we have some size limits in user space. How big can an event record
> > be if the file is MAX_PATH name length and it has a space in its name or
> > directory and each context is it's maximum size? We may need to think
> > about how this might change the whole userspace ecosystem's size
> > definition, MAX_AUDIT_MESSAGE_LENGTH, since this is part of the ABI. And
> > the kernel also has AUDIT_MESSAGE_TEXT_MAX. What would you get with:
> > 
> > # /usr/sbin/auditctl -m `perl -e 'print "A"x8880'`
> > 
> > And last...what about auditctl? Is the syscall filter going to allow
> > filtering on these other subject/object components?
> > 
> > -Steve




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