[refpolicy] MLS file upgrade

[cpebenito@tresys.com (Christopher J. PeBenito)]

On 02/02/12 13:26, Paul Clark wrote:
> In my earlier attempts to debug this desired ability to have all processes have file upgrade capabilities, I reset the type on 'testfile' to user_t (in permissive mode) to try to remove as many variables as possible from the problem, but I guess I introduced more problems.
> 
> When I leave the type as user_home_t, it still fails:
> ls -Z
>     user_u:object_r:user_home_t:s0 testfile
> id -Z
>     user_u:user_r:user_t:s0
> chcon -l s1 testfile
>     chcon: failed to change context of 'testfile' to 'user_u:object_r:user_home_t:s1': Permission denied
> chcon runs with the following context:
>     user_u:user_r:user_t:s0
> 
> It now is reporting a 'relabelto' error.  I changed the 2nd MLS 'mlsconstrain' rule in 'policy/mls' that applies to 'relabelto' from
>     ( h1 dom h2 )
> to
>    ( l1 domby l2)

Thats not going to do anything in this case, as in your test, l1 == h1 and l2 == h2, since both your subject and object are single level.
 
> When I run sealert:
[...]
> Source Context                user_u:user_r:user_t:s0
> Target Context                user_u:object_r:user_home_t:s1
> Target Objects                /home/user2/Documents/testfile [ file ]
[...]
> node=sel13.ern.nps.edu type=AVC msg=audit(1328206230.964:56): avc:  denied  { relabelto } for  pid=2093 comm="chcon" name="testfile" dev=sda1 ino=526347 scontext=user_u:user_r:user_t:s0 tcontext=user_u:object_r:user_home_t:s1 tclass=file

I did a quick look through the MLS constraints, and I /think/ this will achieve what you want.  It should remove all of the upgrading restrictions, except the relabelfrom one.  If you wanted to upgrade a file but your process doesn't dominate the object level (eg subject is s0 and object is s1) you'd have to remove the relabelfrom permission from the MLS constraint for all the file classes.

diff --git a/policy/mls b/policy/mls
index 0e8474b..9a8011b 100644
--- a/policy/mls
+++ b/policy/mls
@@ -68,10 +68,6 @@ gen_levels(mls_num_sens,mls_num_cats)
 mlsconstrain { file lnk_file fifo_file } { create relabelto }
 	( l2 eq h2 );
 
-# new file labels must be dominated by the relabeling subjects clearance
-mlsconstrain { dir file lnk_file chr_file blk_file sock_file fifo_file } relabelto
-	( h1 dom h2 );
-
 # the file "read" ops (note the check is dominance of the low level)
 mlsconstrain { dir file lnk_file chr_file blk_file sock_file fifo_file } { read getattr execute }
 	(( l1 dom l2 ) or
@@ -108,12 +104,10 @@ mlsconstrain dir { add_name remove_name reparent rmdir }
 
 # the file upgrade/downgrade rule
 mlsvalidatetrans { dir file lnk_file chr_file blk_file sock_file fifo_file }
-	((( l1 eq l2 ) or
-	  (( t3 == mlsfileupgrade ) and ( l1 domby l2 )) or
+	((( l1 domby l2 ) or
 	  (( t3 == mlsfiledowngrade ) and ( l1 dom l2 )) or
 	  (( t3 == mlsfiledowngrade ) and ( l1 incomp l2 ))) and
-	 (( h1 eq h2 ) or
-	  (( t3 == mlsfileupgrade ) and ( h1 domby h2 )) or
+	 (( h1 domby h2 ) or
 	  (( t3 == mlsfiledowngrade ) and ( h1 dom h2 )) or
 	  (( t3 == mlsfiledowngrade ) and ( h1 incomp h2 ))));
 
@@ -121,12 +115,10 @@ mlsvalidatetrans { dir file lnk_file chr_file blk_file sock_file fifo_file }
 # has used setfscreate (note that both the high and low level of the object
 # default to the process sensitivity level)
 mlsconstrain { dir file lnk_file chr_file blk_file sock_file fifo_file } create
-	((( l1 eq l2 ) or
-	  (( t1 == mlsfileupgrade ) and ( l1 domby l2 )) or
+	((( l1 domby l2 ) or
 	  (( t1 == mlsfiledowngrade ) and ( l1 dom l2 )) or
 	  (( t1 == mlsfiledowngrade ) and ( l1 incomp l2 ))) and
-	 (( l1 eq h2 ) or
-	  (( t1 == mlsfileupgrade ) and ( l1 domby h2 )) or
+	 (( l1 domby h2 ) or
 	  (( t1 == mlsfiledowngrade ) and ( l1 dom h2 )) or
 	  (( t1 == mlsfiledowngrade ) and ( l1 incomp h2 ))));
 


 
> On 2/2/12 7:23 AM, Christopher J. PeBenito wrote:
>> On 02/01/12 20:09, Paul Clark wrote:
>>> I want to change the MLS policy to allow any process to upgrade a file or directory, but I'm currently failing on an "easy" first step with a "relabelfrom" error.
>>>
>>> I'm using Fedora 13 and selinux-policy-3.7.19-101.fc13.src.rpm.
>>>
>>> I did *not* change the mlscontrain rule that deals with relabelfrom because I think it should still work.
>>>
>>> My test file has the same type that chcon runs with (user_t), and I'm simply trying to change the level from s0 to s1 by doing the following:
>>>      chcon -l s1 testfile
>> Can you clarify this?  It sounds like you're saying that your file is labeled user_t.  If thats the case, then its a regular TE problem, as user_t isn't a file type, so you can't relabel it.
>>
>>> I changed the mlsvalidatetrans statement for "dir" and "file" so that the first line was changed from
>>>      ((( l1 eq l2 ) or
>>> to
>>>      ((( l1 domby l2 ) or
>>>
>>> Any obvious problems or suggestions?
>>>
>>> Another approach would be to also give all domains the "mlsfileupgrade" attribute.  Because my test process was running with user_t, I added:
>>>      mls_file_upgrade(user_t)
>>> to modules/admin/usermanage.te, but there was no change in the error.
>>


-- 
Chris PeBenito
Tresys Technology, LLC
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