variables: fix filter on List RPC

The List RPC correctly authorized against the prefix argument. But when
filtering results underneath the prefix, it only checked authorization for
standard ACL tokens and not Workload Identity. This results in WI tokens being
able to read List results (metadata only: variable paths and timestamps) for
variables under the `nomad/` prefix that belong to other jobs in the same
namespace.

Fixes the filtering and split the `handleMixedAuthEndpoint` function into
separate authentication and authorization steps so that we don't need to
re-verify the claim token on each filtered object.

Also includes:
* update semgrep rule for mixed auth endpoints
* variables: List returns empty set when all results are filtered

.changelog/15012.txt

@@ -0,0 +1,7 @@
+```security
+variables: Fixed a bug where non-sensitive variable metadata (paths and raft indexes) was exposed via the template `nomadVarList` function to other jobs in the same namespace.
+```
+
+```bug
+variables: Fixed a bug where getting empty results from listing variables resulted in a permission denied error.
+```

.semgrep/rpc_endpoint.yml

@@ -45,6 +45,15 @@ rules:
           ...
           ... := $T.handleMixedAuthEndpoint(...)
           ...
+      # Pattern used by endpoints that support both normal ACLs and
+      # workload identity but break authentication and authorization up
+      - pattern-not-inside: |
+          if done, err := $A.$B.forward($METHOD, ...); done {
+            return err
+          }
+          ...
+          ... := $T.authorize(...)
+          ...
       # Pattern used by some Node endpoints.
       - pattern-not-inside: |
           if done, err := $A.$B.forward($METHOD, ...); done {

nomad/variables_endpoint.go

@@ -218,7 +218,7 @@ func (sv *Variables) Read(args *structs.VariablesReadRequest, reply *structs.Var
 	}
 	defer metrics.MeasureSince([]string{"nomad", "variables", "read"}, time.Now())
 
-	_, err := sv.handleMixedAuthEndpoint(args.QueryOptions,
+	_, _, err := sv.handleMixedAuthEndpoint(args.QueryOptions,
 		acl.PolicyRead, args.Path)
 	if err != nil {
 		return err
@@ -269,8 +269,7 @@ func (sv *Variables) List(
 		return sv.listAllVariables(args, reply)
 	}
 
-	aclObj, err := sv.handleMixedAuthEndpoint(args.QueryOptions,
-		acl.PolicyList, args.Prefix)
+	aclObj, claims, err := sv.authenticate(args.QueryOptions)
 	if err != nil {
 		return err
 	}
@@ -299,9 +298,12 @@ func (sv *Variables) List(
 			filters := []paginator.Filter{
 				paginator.GenericFilter{
 					Allow: func(raw interface{}) (bool, error) {
-						sv := raw.(*structs.VariableEncrypted)
-						return strings.HasPrefix(sv.Path, args.Prefix) &&
-							(aclObj == nil || aclObj.AllowVariableOperation(sv.Namespace, sv.Path, acl.PolicyList)), nil
+						v := raw.(*structs.VariableEncrypted)
+						if !strings.HasPrefix(v.Path, args.Prefix) {
+							return false, nil
+						}
+						err := sv.authorize(aclObj, claims, v.Namespace, acl.PolicyList, v.Path)
+						return err == nil, nil
 					},
 				},
 			}
@@ -345,43 +347,23 @@ func (sv *Variables) List(
 
 // listAllVariables is used to list variables held within
 // state where the caller has used the namespace wildcard identifier.
-func (s *Variables) listAllVariables(
+func (sv *Variables) listAllVariables(
 	args *structs.VariablesListRequest,
 	reply *structs.VariablesListResponse) error {
 
 	// Perform token resolution. The request already goes through forwarding
 	// and metrics setup before being called.
-	aclObj, err := s.srv.ResolveToken(args.AuthToken)
+	aclObj, claims, err := sv.authenticate(args.QueryOptions)
 	if err != nil {
 		return err
 	}
 
-	// allowFunc checks whether the caller has the read-job capability on the
-	// passed namespace.
-	allowFunc := func(ns string) bool {
-		return aclObj.AllowVariableOperation(ns, "", acl.PolicyList)
-	}
-
 	// Set up and return the blocking query.
-	return s.srv.blockingRPC(&blockingOptions{
+	return sv.srv.blockingRPC(&blockingOptions{
 		queryOpts: &args.QueryOptions,
 		queryMeta: &reply.QueryMeta,
 		run: func(ws memdb.WatchSet, stateStore *state.StateStore) error {
 
-			// Identify which namespaces the caller has access to. If they do
-			// not have access to any, send them an empty response. Otherwise,
-			// handle any error in a traditional manner.
-			_, err := allowedNSes(aclObj, stateStore, allowFunc)
-			switch err {
-			case structs.ErrPermissionDenied:
-				reply.Data = make([]*structs.VariableMetadata, 0)
-				return nil
-			case nil:
-				// Fallthrough.
-			default:
-				return err
-			}
-
 			// Get all the variables stored within state.
 			iter, err := stateStore.Variables(ws)
 			if err != nil {
@@ -396,15 +378,17 @@ func (s *Variables) listAllVariables(
 				paginator.StructsTokenizerOptions{
 					WithNamespace: true,
 					WithID:        true,
-				},
-			)
+				})
 
 			filters := []paginator.Filter{
 				paginator.GenericFilter{
 					Allow: func(raw interface{}) (bool, error) {
-						sv := raw.(*structs.VariableEncrypted)
-						return strings.HasPrefix(sv.Path, args.Prefix) &&
-							(aclObj == nil || aclObj.AllowVariableOperation(sv.Namespace, sv.Path, acl.PolicyList)), nil
+						v := raw.(*structs.VariableEncrypted)
+						if !strings.HasPrefix(v.Path, args.Prefix) {
+							return false, nil
+						}
+						err := sv.authorize(aclObj, claims, v.Namespace, acl.PolicyList, v.Path)
+						return err == nil, nil
 					},
 				},
 			}
@@ -413,8 +397,8 @@ func (s *Variables) listAllVariables(
 			// responsible for appending a variable to the stubs array.
 			paginatorImpl, err := paginator.NewPaginator(iter, tokenizer, filters, args.QueryOptions,
 				func(raw interface{}) error {
-					sv := raw.(*structs.VariableEncrypted)
-					svStub := sv.VariableMetadata
+					v := raw.(*structs.VariableEncrypted)
+					svStub := v.VariableMetadata
 					svs = append(svs, &svStub)
 					return nil
 				})
@@ -437,7 +421,7 @@ func (s *Variables) listAllVariables(
 
 			// Use the index table to populate the query meta as we have no way
 			// of tracking the max index on deletes.
-			return s.srv.setReplyQueryMeta(stateStore, state.TableVariables, &reply.QueryMeta)
+			return sv.srv.setReplyQueryMeta(stateStore, state.TableVariables, &reply.QueryMeta)
 		},
 	})
 }
@@ -475,24 +459,31 @@ func (sv *Variables) decrypt(v *structs.VariableEncrypted) (*structs.VariableDec
 
 // handleMixedAuthEndpoint is a helper to handle auth on RPC endpoints that can
 // either be called by external clients or by workload identity
-func (sv *Variables) handleMixedAuthEndpoint(args structs.QueryOptions, cap, pathOrPrefix string) (*acl.ACL, error) {
+func (sv *Variables) handleMixedAuthEndpoint(args structs.QueryOptions, cap, pathOrPrefix string) (*acl.ACL, *structs.IdentityClaims, error) {
+
+	aclObj, claims, err := sv.authenticate(args)
+	if err != nil {
+		return aclObj, claims, err
+	}
+	err = sv.authorize(aclObj, claims, args.RequestNamespace(), cap, pathOrPrefix)
+	if err != nil {
+		return aclObj, claims, err
+	}
+
+	return aclObj, claims, nil
+}
+
+func (sv *Variables) authenticate(args structs.QueryOptions) (*acl.ACL, *structs.IdentityClaims, error) {
 
 	// Perform the initial token resolution.
 	aclObj, err := sv.srv.ResolveToken(args.AuthToken)
 	if err == nil {
-		// Perform our ACL validation. If the object is nil, this means ACLs
-		// are not enabled, otherwise trigger the allowed namespace function.
-		if aclObj != nil {
-			if !aclObj.AllowVariableOperation(args.RequestNamespace(), pathOrPrefix, cap) {
-				return nil, structs.ErrPermissionDenied
-			}
-		}
-		return aclObj, nil
+		return aclObj, nil, nil
 	}
 	if helper.IsUUID(args.AuthToken) {
 		// early return for ErrNotFound or other errors if it's formed
 		// like an ACLToken.SecretID
-		return nil, err
+		return nil, nil, err
 	}
 
 	// Attempt to verify the token as a JWT with a workload
@@ -502,27 +493,46 @@ func (sv *Variables) handleMixedAuthEndpoint(args structs.QueryOptions, cap, pat
 		metrics.IncrCounter([]string{
 			"nomad", "variables", "invalid_allocation_identity"}, 1)
 		sv.logger.Trace("allocation identity was not valid", "error", err)
-		return nil, structs.ErrPermissionDenied
+		return nil, nil, structs.ErrPermissionDenied
 	}
+	return nil, claims, nil
+}
 
-	// The workload identity gets access to paths that match its
-	// identity, without having to go thru the ACL system
-	err = sv.authValidatePrefix(claims, args.RequestNamespace(), pathOrPrefix)
-	if err == nil {
-		return aclObj, nil
+func (sv *Variables) authorize(aclObj *acl.ACL, claims *structs.IdentityClaims, ns, cap, pathOrPrefix string) error {
+
+	if aclObj == nil && claims == nil {
+		return nil // ACLs aren't enabled
 	}
 
-	// If the workload identity doesn't match the implicit permissions
-	// given to paths, check for its attached ACL policies
-	aclObj, err = sv.srv.ResolveClaims(claims)
-	if err != nil {
-		return nil, err // this only returns an error when the state store has gone wrong
+	// Perform normal ACL validation. If the ACL object is nil, that means we're
+	// working with an identity claim.
+	if aclObj != nil {
+		if !aclObj.AllowVariableOperation(ns, pathOrPrefix, cap) {
+			return structs.ErrPermissionDenied
+		}
+		return nil
 	}
-	if aclObj != nil && aclObj.AllowVariableOperation(
-		args.RequestNamespace(), pathOrPrefix, cap) {
-		return aclObj, nil
+
+	if claims != nil {
+		// The workload identity gets access to paths that match its
+		// identity, without having to go thru the ACL system
+		err := sv.authValidatePrefix(claims, ns, pathOrPrefix)
+		if err == nil {
+			return nil
+		}
+
+		// If the workload identity doesn't match the implicit permissions
+		// given to paths, check for its attached ACL policies
+		aclObj, err = sv.srv.ResolveClaims(claims)
+		if err != nil {
+			return err // this only returns an error when the state store has gone wrong
+		}
+		if aclObj != nil && aclObj.AllowVariableOperation(
+			ns, pathOrPrefix, cap) {
+			return nil
+		}
 	}
-	return nil, structs.ErrPermissionDenied
+	return structs.ErrPermissionDenied
 }
 
 // authValidatePrefix asserts that the requested path is valid for