Re: SNMP/VACM: bugfix for vacmViewTreeFamilyMask

From aa2acfb8a0b5ae05fc5ba982d78ee5607384a2be Mon Sep 17 00:00:00 2001
From: Stefan Zegenhagen <[email protected]>
Date: Wed, 1 Aug 2012 09:56:15 +0200
Subject: [PATCH] bugfix for vacmViewTreeFamilyMask

The vacmViewTreeFamilyMask is defined to be a bit string in the MIB, not
an OID. However, the MIB implementation assumed the latter, effectively
rendering all attempts to read/set masks via SNMP unsuccessful.

Since the mask is used in hot paths (e.g. access permission checks for
each SNMP operation, the OID representation of the mask has benefits
(e.g. faster processing). Therefore, convert the bitstring to/from its
OID representation when reading/setting any mask object.
---
 lib/snmp/src/agent/snmp_view_based_acm_mib.erl |   91 ++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 6 deletions(-)

diff --git a/lib/snmp/src/agent/snmp_view_based_acm_mib.erl b/lib/snmp/src/agent/snmp_view_based_acm_mib.erl
index 71dcc0f..56fbf90 100644
--- a/lib/snmp/src/agent/snmp_view_based_acm_mib.erl
+++ b/lib/snmp/src/agent/snmp_view_based_acm_mib.erl
@@ -949,9 +949,9 @@ verify_vacmViewTreeFamilyTable_col(?vacmViewTreeFamilyMask, Mask) ->
 	null -> [];
 	[]   -> [];
 	_ ->
-	    case (catch snmp_conf:check_oid(Mask)) of
+	    case (catch check_mask(Mask)) of
 		ok ->
-		    Mask;
+		    mask2oid(Mask);
 	        _ ->
 		    wrongValue(?vacmViewTreeFamilyMask)
 	    end
@@ -967,7 +967,54 @@ verify_vacmViewTreeFamilyTable_col(?vacmViewTreeFamilyType, Type) ->
     end;
 verify_vacmViewTreeFamilyTable_col(_, Val) ->
     Val.
-	    
+
+
+check_mask([]) ->
+    ok;
+check_mask([Head | Tail]) when is_integer(Head) ->
+% we can cause exception here because the caller catches
+    if
+        Head > -1 andalso Head < 256 ->
+            check_mask(Tail)
+    end.
+
+% internally (for easier computations), the mask is stored
+% as OID and not as bit-field. Therefore, we have to convert
+% the bitstring to a list of integers before storing it.
+mask2oid(Mask) ->
+    Func = fun(Byte) ->
+            % what's a nice syntax for extracting bits
+            % from a byte???
+            <<A:1, B:1, C:1, D:1, E:1, F:1, G:1, H:1>> = <<Byte>>,
+            [A, B, C, D, E, F, G, H]
+    end,
+    lists:flatten(lists:map(Func, Mask)).
+
+oid2mask(Oid) ->
+    % convert all suboids to either 1 or 0 for sure
+    Func = fun
+        (0) -> 0;
+        (_) -> 1
+    end,
+    oid2mask(lists:map(Func, Oid), []).
+
+oid2mask([], Mask) ->
+    % end-of-list, return bitstring
+    lists:reverse(Mask);
+oid2mask(Oid, Mask) ->
+    % check whether we've got at least 8 sub-identifiers. if not,
+    % extend with 1's until there are enough to fill a byte
+    NOid = case length(Oid) of
+        Small when Small < 8 ->
+            Oid ++ lists:duplicate(8-Small, 1);
+        _ ->
+            Oid
+    end,
+    % extract sufficient suboids for 8 bits
+    [A, B, C, D, E, F, G, H | Tail] = NOid,
+    <<Byte:8>> = <<A:1, B:1, C:1, D:1, E:1, F:1, G:1, H:1>>,
+    oid2mask(Tail, [Byte | Mask]).
+
 
 table_next(Name, RestOid) ->
     snmp_generic:table_next(db(Name), RestOid).
@@ -1006,11 +1053,43 @@ stc(vacmSecurityToGroupTable) -> ?vacmSecurityToGroupStorageType;
 stc(vacmViewTreeFamilyTable) -> ?vacmViewTreeFamilyStorageType.
  
 next(Name, RowIndex, Cols) ->
-    snmp_generic:handle_table_next(db(Name), RowIndex, Cols,
-                                   fa(Name), foi(Name), noc(Name)).
+    Ans = snmp_generic:handle_table_next(db(Name), RowIndex, Cols,
+                                   fa(Name), foi(Name), noc(Name)),
+    patch_next(Name, Ans).
  
 get(Name, RowIndex, Cols) ->
-    snmp_generic:handle_table_get(db(Name), RowIndex, Cols, foi(Name)).
+    Ans = snmp_generic:handle_table_get(db(Name), RowIndex, Cols, foi(Name)),
+    patch(Name, Cols, Ans).
+
+
+patch(Name, Cols, Ans) when is_list(Ans) ->
+    % function to patch returned values
+    Func = fun
+        ({Col, {value, Val}}) ->    {value, do_patch(Name, Col, Val)};
+        ({_, Other}) ->             Other
+    end,
+    % merge column numbers and return values. there must be as much
+    % return values as there are columns requested
+    Tmp = lists:zip(Cols, Ans),
+    % and patch all values
+    lists:map(Func, Tmp);
+patch(_, _, Ans) ->
+    Ans.
+
+patch_next(Name, Ans) when is_list(Ans) ->
+    Func = fun
+        ({[C | _] = Idx, Val}) ->   {Idx, do_patch(Name, C, Val)};
+        (Other) ->                  Other
+    end,
+    lists:map(Func, Ans);
+patch_next(_, Ans) ->
+    Ans.
+
+do_patch(vacmViewTreeFamilyTable, ?vacmViewTreeFamilyMask, Val) ->
+    oid2mask(Val);
+do_patch(_, _, Val) ->
+    Val.
+
 
 wrongValue(V) -> throw({wrongValue, V}).
 
-- 
1.7.9.5