keystore/grant_store.h

/*
 * 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& owner_dir_name, const uid_t owner_uid,
          const uint64_t grant_no);
    // the following three field are used to recover the key filename that the grant refers to
    std::string alias_;            ///< original/wrapped key alias
    std::string owner_dir_name_;   ///< key owner key directory
    uid_t owner_uid_;              ///< key owner uid

    uint64_t grant_no_;            ///< numeric grant identifier - randomly assigned

    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& owner_dir_name,
                    const uid_t owner_uid);
    const Grant* get(const uid_t uid, const std::string& alias) const;
    bool removeByFileAlias(const uid_t granteeUid, const uid_t granterUid, const std::string& alias);
    void removeAllGrantsToKey(const uid_t granterUid, const std::string& alias);
    void removeAllGrantsToUid(const uid_t granteeUid);

    // 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_