path: root/src/mongo/base/secure_allocator.h

/**
 *    Copyright (C) 2018-present MongoDB, Inc.
 *
 *    This program is free software: you can redistribute it and/or modify
 *    it under the terms of the Server Side Public License, version 1,
 *    as published by MongoDB, Inc.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    Server Side Public License for more details.
 *
 *    You should have received a copy of the Server Side Public License
 *    along with this program. If not, see
 *    <http://www.mongodb.com/licensing/server-side-public-license>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the Server Side Public License in all respects for
 *    all of the code used other than as permitted herein. If you modify file(s)
 *    with this exception, you may extend this exception to your version of the
 *    file(s), but you are not obligated to do so. If you do not wish to do so,
 *    delete this exception statement from your version. If you delete this
 *    exception statement from all source files in the program, then also delete
 *    it in the license file.
 */

#pragma once

#include "mongo/config.h"

#include <cstddef>
#include <limits>
#include <memory>
#include <string>
#include <type_traits>
#include <vector>

#include "mongo/base/static_assert.h"
#include "mongo/db/server_options.h"
#include "mongo/stdx/type_traits.h"
#include "mongo/util/assert_util.h"

namespace mongo {

namespace secure_allocator_details {

void* allocate(std::size_t bytes, std::size_t alignOf);
void deallocate(void* ptr, std::size_t bytes);

inline void* allocateWrapper(std::size_t bytes, std::size_t alignOf, bool secure) {
    if (secure) {
        return allocate(bytes, alignOf);
    } else {
        return mongoMalloc(bytes);
    }
}
inline void deallocateWrapper(void* ptr, std::size_t bytes, bool secure) {
    if (secure) {
        return deallocate(ptr, bytes);
    } else {
        return free(ptr);
    }
}

}  // namespace secure_allocator_details

/**
 * Provides a secure allocator for trivially copyable types. By secure we mean
 * memory that will be zeroed on free and locked out of paging while in memory
 * (to prevent it from being written to disk).
 *
 * While this type can be used with any allocator aware container, it should be
 * considered whether either of the two named specializations below are
 * sufficient (a string and a vector). The allocations out of this container
 * are quite expensive, so one should endeavor to use containers which make
 * few, contiguous allocations where possible.
 *
 * Note that this allocator is written without reling on default
 * semantics injected via allocator_traits, and so defines all
 * optional allocator members, and does not rely on allocator_traits
 * to default them in. See http://stackoverflow.com/a/33267132 for a
 * rationale for GCC 4.8, our current default compiler. There is also
 * evidence that MSVC 2013's _DEBUG STL does not work correctly with
 * allocator_traits.
 *
 * See also: http://howardhinnant.github.io/allocator_boilerplate.html
 */
template <typename DomainTraits>
struct SecureAllocatorDomain {
    template <typename T>
    struct SecureAllocator {
        /**
         * We only support trivially copyable types to avoid situations where the
         * SecureAllocator is used in containers with complex types that do their
         * own allocation. I.e. one could otherwise have a:
         *
         * std::vector<std::string, SecureAllocator<std::string>>
         *
         * where the vectors were stored securely, but the strings spilled to the
         * heap
         *
         */
        MONGO_STATIC_ASSERT_MSG(std::is_trivially_copyable<T>::value,
                                "SecureAllocator can only be used with trivially copyable types");

        // NOTE: The standard doesn't seem to require these, but libstdc++
        // definitly wants them.
        using reference = T&;
        using const_reference = const T&;


        // NOTE: These members are defined in the same order as specified
        // in the "Allocator Requirements" section of the standard. Please
        // retain this ordering.

        using pointer = T*;
        using const_pointer = const T*;
        using void_pointer = void*;
        using const_void_pointer = const void*;
        using value_type = T;
        using size_type = std::size_t;
        using difference_type = std::ptrdiff_t;

        template <typename U>
        struct rebind {
            using other = SecureAllocator<U>;
        };

        pointer allocate(size_type n) {
            return static_cast<pointer>(secure_allocator_details::allocateWrapper(
                sizeof(value_type) * n, std::alignment_of<T>::value, DomainTraits::peg()));
        }

        pointer allocate(size_type n, const_void_pointer) {
            return allocate(n);
        }

        void deallocate(pointer ptr, size_type n) {
            return secure_allocator_details::deallocateWrapper(
                static_cast<void*>(ptr), sizeof(value_type) * n, DomainTraits::peg());
        }

        size_type max_size() {
            return std::numeric_limits<size_type>::max();
        }

        SecureAllocator() = default;

        template <typename U>
        SecureAllocator(const SecureAllocator<U>& other) {}

        template <typename U, typename... Args>
        void construct(U* p, Args&&... args) {
            ::new (static_cast<void*>(p)) U(std::forward<Args>(args)...);
        }

        template <typename U>
        void destroy(U* p) {
            p->~U();
        }

        SecureAllocator select_on_container_copy_construction() {
            // SecureAllocator is stateless, so just return a default
            // constructed instance.
            return SecureAllocator();
        }

        // For background:
        //
        // http://stackoverflow.com/questions/27471053/example-usage-of-propagate-on-container-move-assignment
        //
        // https://foonathan.github.io/blog/2015/10/05/allocatorawarecontainer-propagation-pitfalls.html
        //
        // This allocator is stateless, so we can avoid a runtime check
        // (even though it would probably be optimized out based on the
        // constrexpr-esque nature of our equality comparison operator),
        // so we can set all of these to true.
        using propagate_on_container_copy_assignment = std::true_type;
        using propagate_on_container_move_assignment = std::true_type;
        using propagate_on_container_swap = std::true_type;

        using is_always_equal = std::true_type;
    };

    template <typename T, typename U>
    friend bool operator==(const SecureAllocator<T>& lhs, const SecureAllocator<U>& rhs) {
        // Note: If you change this, you must re-evaluate the select_ and
        // propagate_ methods and typedefs above.
        return true;
    }

    template <typename T, typename U>
    friend bool operator!=(const SecureAllocator<T>& lhs, const SecureAllocator<U>& rhs) {
        return !(lhs == rhs);
    }

    /**
     * SecureHandle offers a smart pointer-ish interface to a type.
     *
     * It attempts to solve the problem of using container types with small object optimizations
     * that
     * might accidentally leave important data on the stack if they're too small to spill to the
     * heap.
     * It uses the secure allocator for allocations and deallocations.
     *
     * This type is meant to offer more value like semantics than a unique_ptr:
     *   - SecureHandle's are only default constructible if their T is
     *   - You can construct a SecureHandle like the underlying value:
     *       SecureHandle<Mytype> type(foo, bar baz);
     *   - SecureHandle's are copyable if their T's are
     *   - only moving can produce a non-usable T
     *
     * While still being cheap and convenient like a unique_ptr:
     *   - SecureHandle's move by pointer to their secure storage
     *   - T& operator*()
     *   - T* operator->()
     *
     * In a moved from state, SecureHandle's may be copy or move assigned and the destructor may
     * run,
     * but all other operations will invariant.
     */
    template <typename T>
    class SecureHandle {
    public:
        // NOTE: (jcarey)
        //
        // We have the default ctor and the perfect forwarding ctor because msvc 2013 ice's on some
        // default constructed types without it (sfinae was falling over for some reason).
        //
        // For non-default constructible t's, we'll fail to substitute the forwarded call to new
        SecureHandle() : _t(_new()) {}

        // Generic constructor that forwards to the underlying T if the first arg isn't a
        // SecureHandle
        template <
            typename Arg,
            typename... Args,
            stdx::enable_if_t<!std::is_same<SecureHandle<T>, typename std::decay<Arg>::type>::value,
                              int> = 0>
        SecureHandle(Arg&& arg, Args&&... args)
            : _t(_new(std::forward<Arg>(arg), std::forward<Args>(args)...)) {}

        SecureHandle(const SecureHandle& other) : _t(_new(*other)) {}

        SecureHandle& operator=(const SecureHandle& other) {
            if (_t) {
                *_t = *other;
            } else {
                _t = _new(*other);
            }

            return *this;
        }

        SecureHandle(SecureHandle&& other) : _t(other._t) {
            other._t = nullptr;
        }

        SecureHandle& operator=(SecureHandle&& other) {
            if (&other == this) {
                return *this;
            }

            _delete();

            _t = other._t;
            other._t = nullptr;

            return *this;
        }

        ~SecureHandle() {
            _delete();
        }

        T& operator*() const {
            invariant(_t);

            return *_t;
        }

        T* operator->() const {
            invariant(_t);

            return _t;
        }

    private:
        template <typename... Args>
        static T* _new(Args&&... args) {
            return ::new (secure_allocator_details::allocateWrapper(
                sizeof(T), std::alignment_of<T>::value, DomainTraits::peg()))
                T(std::forward<Args>(args)...);
        }

        void _delete() {
            if (_t) {
                _t->~T();
                secure_allocator_details::deallocateWrapper(_t, sizeof(T), DomainTraits::peg());
            }
        }

        T* _t;
    };

    template <typename T>
    using SecureVector = SecureHandle<std::vector<T, SecureAllocator<T>>>;

    using SecureString =
        SecureHandle<std::basic_string<char, std::char_traits<char>, SecureAllocator<char>>>;
};

struct SecureAllocatorDefaultDomainTrait {
    constexpr static bool peg() {
        return true;
    }
};

struct SecureAllocatorAuthDomainTrait {
    static constexpr StringData DomainType = "auth"_sd;
};

using SecureAllocatorAuthDomain =
    SecureAllocatorDomain<TraitNamedDomain<SecureAllocatorAuthDomainTrait>>;

using SecureAllocatorDefaultDomain = SecureAllocatorDomain<SecureAllocatorDefaultDomainTrait>;

template <typename T>
using SecureVector = SecureAllocatorDefaultDomain::SecureVector<T>;
using SecureString = SecureAllocatorDefaultDomain::SecureString;

}  // namespace mongo