Refurbish granting mechanism
Keystore stores key blobs in with filenames that include the symbolic
name and the uid of the owner. This behaviour should have been
completely opaque to the user keystore. However, the granting mechanism,
by which an app can allow another app to use one of its keys, leaked the
internal structure in that the grantee had to specify the key name with
the granter's uid prefix in order to use the granted key. This in turn
collided with prefix handling in other parts of the framework.
This patch refurbishes the granting mechanism such that keystore can
choose a name for the grant. It uses the original symbolic key name as
prefix and appends _KEYSTOREGRANT_<grant_no> where the grant_no is
chosen as first free slot starting from 0. Each uid has its own grant_no
space.
This changes the grant call such that it now returns a string, which is
the alias name of the newly created grant. The string is empty if the
grant operation failed.
As before apps can still mask granted keys by importing a key with the
exact same name including the added suffix. But everybody deserves the
right to shoot themselves in the foot if they really want to.
Bug: 37264540
Bug: 62237038
Test: run cts-dev --module CtsDevicePolicyManagerTestCases --test
com.android.cts.devicepolicy.DeviceOwnerTest#testKeyManagement
because it grants a key
Change-Id: I723c44c7ae6782c8de42063744717d088cd49ba1
diff --git a/keystore/grant_store.h b/keystore/grant_store.h
new file mode 100644
index 0000000..43e814e
--- /dev/null
+++ b/keystore/grant_store.h
@@ -0,0 +1,68 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef KEYSTORE_GRANT_STORE_H_
+#define KEYSTORE_GRANT_STORE_H_
+
+#include <set>
+#include <string>
+#include <unordered_map>
+
+namespace keystore {
+
+/**
+ * Grant represents a mapping from an alias to a key file.
+ * Normally, key file names are derived from the alias chosen by the client
+ * and the clients UID, to generate a per client name space.
+ * Grants allow assotiating a key file with a new name, thereby making
+ * it visible in another client's - the grantee's - namespace.
+ */
+class Grant {
+public:
+ Grant(const std::string& alias, const std::string& key_file, const uint64_t grant_no);
+ std::string alias_;
+ std::string key_file_;
+ uint64_t grant_no_;
+
+ operator const uint64_t&() const { return grant_no_; }
+};
+
+/**
+ * The GrantStore holds a set of sets of Grants. One set of Grants for each grantee.
+ * The uid parameter to each of the GrantStore function determines the grantee's
+ * name space. The methods put, get, and removeByAlias/ByFileName create, lookup, and
+ * remove a Grant, respectively.
+ * put also returns a new alias for the newly granted key which has to be returned
+ * to the granter. The grantee, and only the grantee, can use the granted key
+ * by this new alias.
+ */
+class GrantStore {
+public:
+ GrantStore() : grants_() {}
+ std::string put(const uid_t uid, const std::string& alias, const std::string& key_file);
+ const Grant* get(const uid_t uid, const std::string& alias) const;
+ bool removeByFileName(const uid_t uid, const std::string& filename);
+
+ // GrantStore is neither copyable nor movable.
+ GrantStore(const GrantStore&) = delete;
+ GrantStore& operator=(const GrantStore&) = delete;
+private:
+ std::unordered_map<uid_t, std::set<Grant, std::less<>>> grants_;
+};
+
+} // namespace keystore
+
+#endif // KEYSTORE_GRANT_STORE_H_