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99 lines
3.5 KiB
C++
99 lines
3.5 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_dom_quota_EncryptedBlock_h
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#define mozilla_dom_quota_EncryptedBlock_h
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#include <cstdint>
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#include <cstring>
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#include <limits>
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#include "mozilla/Assertions.h"
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#include "mozilla/Span.h"
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#include "nsTArray.h"
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namespace mozilla::dom::quota {
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// An encrypted block has the following format:
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// - one basic block containing a uint16_t stating the actual payload length
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// - one basic block containing the cipher prefix (tyipically a nonce)
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// - encrypted payload up to the remainder of the specified overall size
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// We currently assume the basic block size is the same as the cipher prefix
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// length.
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//
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// XXX Actually, we don't need the actual payload length in every block. Only
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// the last block may be incomplete. The tricky thing is just that it might be
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// incomplete by just one or two bytes.
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template <size_t CipherPrefixLength, size_t BasicBlockSize>
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class EncryptedBlock {
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public:
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explicit EncryptedBlock(const size_t aOverallSize) {
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MOZ_RELEASE_ASSERT(aOverallSize >
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CipherPrefixOffset() + CipherPrefixLength);
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MOZ_RELEASE_ASSERT(aOverallSize <= std::numeric_limits<uint16_t>::max());
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// XXX Do we need this to be fallible? Then we need a factory/init function.
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// But maybe that's not necessary as the block size is not user-provided and
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// small.
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mData.SetLength(aOverallSize);
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// Bug 1867394: Making sure to zero-initialize first block as there might
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// be some unused bytes in it which could expose sensitive data.
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// Currently, only sizeof(uint16_t) bytes gets used in the first block.
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std::fill(mData.begin(), mData.begin() + CipherPrefixOffset(), 0);
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SetActualPayloadLength(MaxPayloadLength());
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}
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size_t MaxPayloadLength() const {
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return mData.Length() - CipherPrefixLength - CipherPrefixOffset();
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}
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void SetActualPayloadLength(uint16_t aActualPayloadLength) {
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memcpy(mData.Elements(), &aActualPayloadLength, sizeof(uint16_t));
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}
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size_t ActualPayloadLength() const {
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return *reinterpret_cast<const uint16_t*>(mData.Elements());
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}
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using ConstSpan = Span<const uint8_t>;
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using MutableSpan = Span<uint8_t>;
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ConstSpan CipherPrefix() const {
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return WholeBlock().Subspan(CipherPrefixOffset(), CipherPrefixLength);
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}
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MutableSpan MutableCipherPrefix() {
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return MutableWholeBlock().Subspan(CipherPrefixOffset(),
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CipherPrefixLength);
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}
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ConstSpan Payload() const {
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return WholeBlock()
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.SplitAt(CipherPrefixOffset() + CipherPrefixLength)
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.second.First(RoundedUpToBasicBlockSize(ActualPayloadLength()));
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}
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MutableSpan MutablePayload() {
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return MutableWholeBlock()
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.SplitAt(CipherPrefixOffset() + CipherPrefixLength)
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.second.First(RoundedUpToBasicBlockSize(ActualPayloadLength()));
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}
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ConstSpan WholeBlock() const { return mData; }
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MutableSpan MutableWholeBlock() { return mData; }
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private:
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static constexpr size_t CipherPrefixOffset() {
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return RoundedUpToBasicBlockSize(sizeof(uint16_t));
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}
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static constexpr size_t RoundedUpToBasicBlockSize(const size_t aValue) {
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return (aValue + BasicBlockSize - 1) / BasicBlockSize * BasicBlockSize;
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}
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nsTArray<uint8_t> mData;
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};
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} // namespace mozilla::dom::quota
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#endif
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