mirror of
https://github.com/SerenityOS/serenity
synced 2024-07-05 21:34:57 +00:00
7b50f71e0e
This fixes some errors where too many bytes were allowed to be read for signed integers of a smaller size (e.g. i32). The new parser doesn't make 64-bit assumptions and now matches the generality of its unsigned counterpart. (cherry picked from commit 596dd5252d477747d466e660acca25c015ce12e4)
100 lines
2.9 KiB
C++
100 lines
2.9 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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template<typename ValueType>
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class [[gnu::packed]] LEB128 {
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public:
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constexpr LEB128() = default;
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constexpr LEB128(ValueType value)
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: m_value(value)
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{
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}
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constexpr operator ValueType() const { return m_value; }
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static ErrorOr<LEB128<ValueType>> read_from_stream(Stream& stream)
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requires(Unsigned<ValueType>)
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{
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ValueType result {};
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size_t num_bytes = 0;
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while (true) {
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if (stream.is_eof())
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return Error::from_string_literal("Stream reached end-of-file while reading LEB128 value");
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auto byte = TRY(stream.read_value<u8>());
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ValueType masked_byte = byte & ~(1 << 7);
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bool const shift_too_large_for_result = num_bytes * 7 > sizeof(ValueType) * 8;
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if (shift_too_large_for_result)
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return Error::from_string_literal("Read value contains more bits than fit the chosen ValueType");
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bool const shift_too_large_for_byte = ((masked_byte << (num_bytes * 7)) >> (num_bytes * 7)) != masked_byte;
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if (shift_too_large_for_byte)
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return Error::from_string_literal("Read byte is too large to fit the chosen ValueType");
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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 LEB128<ValueType> { result };
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}
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static ErrorOr<LEB128<ValueType>> read_from_stream(Stream& stream)
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requires(Signed<ValueType>)
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{
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constexpr auto BITS = sizeof(ValueType) * 8;
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ValueType result = 0;
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u32 shift = 0;
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u8 byte = 0;
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do {
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if (stream.is_eof())
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return Error::from_string_literal("Stream reached end-of-file while reading LEB128 value");
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byte = TRY(stream.read_value<u8>());
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result |= (ValueType)(byte & 0x7F) << shift;
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if (shift >= BITS - 7) {
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bool has_continuation = (byte & 0x80);
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ValueType sign_and_unused = (i8)(byte << 1) >> (BITS - shift);
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if (has_continuation)
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return Error::from_string_literal("Read value contains more bits than fit the chosen ValueType");
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if (sign_and_unused != 0 && sign_and_unused != -1)
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return Error::from_string_literal("Read byte is too large to fit the chosen ValueType");
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return LEB128<ValueType> { result };
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}
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shift += 7;
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} while (byte & 0x80);
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// Sign extend
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if (shift < BITS && (byte & 0x40))
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result |= ((ValueType)~0 << shift);
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return LEB128<ValueType> { result };
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}
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private:
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ValueType m_value { 0 };
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};
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}
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#if USING_AK_GLOBALLY
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using AK::LEB128;
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#endif
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