mirror of
https://github.com/SerenityOS/serenity
synced 2024-07-21 01:55:07 +00:00
0af192ff8d
Previously, we would go crazy and shift things way out of bounds. Add tests to verify that the decoding algorithm is safe around the limits of the result type.
113 lines
3.6 KiB
C++
113 lines
3.6 KiB
C++
/*
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* Copyright (c) 2020-2021, the SerenityOS developers.
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#pragma once
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#include <AK/NumericLimits.h>
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#include <AK/Stream.h>
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#include <AK/Types.h>
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namespace AK {
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struct LEB128 {
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template<typename StreamT, typename ValueType = size_t>
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static bool read_unsigned(StreamT& stream, ValueType& result)
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{
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[[maybe_unused]] size_t backup_offset = 0;
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if constexpr (requires { stream.offset(); })
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backup_offset = stream.offset();
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InputStream& input_stream { stream };
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result = 0;
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size_t num_bytes = 0;
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while (true) {
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if (input_stream.unreliable_eof()) {
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if constexpr (requires { stream.seek(backup_offset); })
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stream.seek(backup_offset);
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input_stream.set_fatal_error();
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return false;
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}
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u8 byte = 0;
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input_stream >> byte;
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if (input_stream.has_any_error())
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return false;
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ValueType masked_byte = byte & ~(1 << 7);
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const bool shift_too_large_for_result = (num_bytes * 7 > sizeof(ValueType) * 8) && (masked_byte != 0);
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const bool shift_too_large_for_byte = ((masked_byte << (num_bytes * 7)) >> (num_bytes * 7)) != masked_byte;
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if (shift_too_large_for_result || shift_too_large_for_byte)
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return false;
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result = (result) | (masked_byte << (num_bytes * 7));
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if (!(byte & (1 << 7)))
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break;
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++num_bytes;
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}
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return true;
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}
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template<typename StreamT, typename ValueType = ssize_t>
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static bool read_signed(StreamT& stream, ValueType& result)
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{
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// Note: We read into a u64 to simplify the parsing logic;
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// result is range checked into ValueType after parsing.
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static_assert(sizeof(ValueType) <= sizeof(u64), "Error checking logic assumes 64 bits or less!");
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[[maybe_unused]] size_t backup_offset = 0;
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if constexpr (requires { stream.offset(); })
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backup_offset = stream.offset();
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InputStream& input_stream { stream };
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i64 temp = 0;
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size_t num_bytes = 0;
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u8 byte = 0;
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result = 0;
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do {
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if (input_stream.unreliable_eof()) {
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if constexpr (requires { stream.seek(backup_offset); })
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stream.seek(backup_offset);
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input_stream.set_fatal_error();
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return false;
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}
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input_stream >> byte;
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if (input_stream.has_any_error())
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return false;
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// note: 64 bit assumptions!
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u64 masked_byte = byte & ~(1 << 7);
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const bool shift_too_large_for_result = (num_bytes * 7 >= 64) && (masked_byte != ((temp < 0) ? 0x7Fu : 0u));
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const bool shift_too_large_for_byte = (num_bytes * 7) == 63 && masked_byte != 0x00 && masked_byte != 0x7Fu;
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if (shift_too_large_for_result || shift_too_large_for_byte)
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return false;
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temp = (temp) | (masked_byte << (num_bytes * 7));
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++num_bytes;
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} while (byte & (1 << 7));
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if ((num_bytes * 7) < 64 && (byte & 0x40)) {
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// sign extend
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temp |= ((u64)(-1) << (num_bytes * 7));
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}
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// Now that we've accumulated into an i64, make sure it fits into result
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if constexpr (sizeof(ValueType) < sizeof(u64)) {
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if (temp > NumericLimits<ValueType>::max() || temp < NumericLimits<ValueType>::min())
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return false;
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}
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result = static_cast<ValueType>(temp);
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return true;
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}
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};
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}
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using AK::LEB128;
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