From mboxrd@z Thu Jan  1 00:00:00 1970
Message-ID: <44C91F31.1070103@mentalrootkit.com>
Date: Thu, 27 Jul 2006 16:16:49 -0400
From: Karl MacMillan <kmacmillan@mentalrootkit.com>
MIME-Version: 1.0
To: Joshua Brindle <jbrindle@tresys.com>
CC: Stephen Smalley <sds@tycho.nsa.gov>, selinux@tycho.nsa.gov
Subject: Re: [PATCH RETRY 2/3] Optionally expand neverallows
References: <6FE441CD9F0C0C479F2D88F959B0158832A937@exchange.columbia.tresys.com>
In-Reply-To: <6FE441CD9F0C0C479F2D88F959B0158832A937@exchange.columbia.tresys.com>
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Sender: owner-selinux@tycho.nsa.gov
List-Id: selinux@tycho.nsa.gov

Joshua Brindle wrote:
>> From: Karl MacMillan [mailto:kmacmillan@mentalrootkit.com] 
>>
>> Joshua Brindle wrote:
>>     
>>> @@ -366,6 +366,7 @@
>>>     uint32_t policy_type;
>>>     char *name;
>>>     char *version;
>>> +    int invalid;
>>>
>>>       
>> Expanding the avrules doesn't really make the policydb 
>> invalid, right? 
>> It just makes it non-standard (tainted :) )
>>
>>     
>
> Putting neverallows in the avtab is invalid (the reader will bail if it
> tries to read one)
>
>   

I disagree - the policydb is still valid, otherwise there would be no 
point doing analysis on it. I think the more correct semantic is that 
this policydb cannot be represented by the on disc format. So the 
variable would be better called something like policydb->unsupported_format.

Wait, just because the neverallows are expanded doesn't mean that the 
unexpanded aren't also there, meaning that the policydb could be written 
to disc with no loss of information. This reinforces my notion that the 
policy is valid. Why not just skip saving the neverallows in the format 
and document the behavior?

>>>     }
>>> @@ -2156,7 +2159,7 @@
>>>         goto cleanup;
>>>     hashtab_map_remove_on_error(state.out->p_types.table,
>>>                     type_attr_remove, type_destroy, state.out);
>>> -    if (check) {
>>> +    if (check && !(out->invalid)) {
>>>         if (hierarchy_check_constraints(handle, state.out))
>>>             goto cleanup;
>>>
>>>       
>> Why disallow hierarchy checking?
>>     
>
> It disables all checking for invalid policies, there is no reason to do
> checking if you've marked a policy invalid since it can't be written
> anyway 

1) The policy is still valid.
2) If this is for analysis I would imagine you would want the 
neverallows and _also_ know if the policy violates hierarchy constraints.
3) It is surprising since the caller explicitly requests both the 
checking and the expansion. If these parameters really are exclusive an 
error should be raised rather than silently not performing the action.

> (invalid will probably mean other things in the future, such as a
> policy with disabled rules expanded out and conflicting type transitions
> in the avtab for access control checking).
>
>   
>>> Index: trunk/libsepol/src/write.c
>>> ===================================================================
>>> --- trunk/libsepol/src/write.c    (revision 951)
>>> +++ trunk/libsepol/src/write.c    (working copy)
>>> @@ -1411,6 +1411,9 @@
>>>     struct policy_data pd;
>>>     char *policydb_str;
>>>
>>> +    if (p->invalid)
>>> +        return -1;
>>> +
>>>       
>> A separate return code is needed so that the caller can 
>> distinguish between general, likely fatal errors and a 
>> policydb that can't be written because the format doesn't support it.
>>
>>     
>
> -2? ;)
>
> -1 is currently used if, for example, policy->policyvers is invalid,
> same deal.. These are programming errors not user errors. I'd be fine
> with it being an assert() personally.
>   

See above - I think that the write should just work and ignore the 
expanded neverallows.

Karl


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