mirror of
https://github.com/RGBCube/serenity
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9a8cc5a98d
Previously, the DNS packet parser would happily parse a DNS packet containing an arbitrarily large domain name. We now limit each segment of a domain name to 63 characters and the total domain name length to 253 characters. This is consistent with RFC1035, which specifies that the maximum name length is 255 octets. This includes the initial length byte and final null byte, which accounts for the 2 byte difference.
111 lines
3.4 KiB
C++
111 lines
3.4 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
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*
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* SPDX-License-Identifier: BSD-2-Clause
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*/
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#include "Name.h"
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#include <AK/Random.h>
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#include <AK/Stream.h>
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#include <AK/Vector.h>
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#include <ctype.h>
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namespace DNS {
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Name::Name(DeprecatedString const& name)
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{
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if (name.ends_with('.'))
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m_name = name.substring(0, name.length() - 1);
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else
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m_name = name;
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}
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ErrorOr<Name> Name::parse(ReadonlyBytes data, size_t& offset, size_t recursion_level)
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{
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static constexpr size_t MAX_LABEL_SIZE = 63;
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static constexpr size_t MAX_NAME_SIZE = 253;
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if (recursion_level > 4)
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return Name {};
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StringBuilder builder;
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while (true) {
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if (offset >= data.size())
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return Error::from_string_literal("Unexpected EOF when parsing name");
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u8 b = data[offset++];
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if (b == '\0') {
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if (builder.length() > MAX_NAME_SIZE)
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return Error::from_string_literal("Domain name exceeds maximum allowed length");
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// This terminates the name.
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return builder.to_deprecated_string();
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} else if ((b & 0xc0) == 0xc0) {
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// The two bytes tell us the offset when to continue from.
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if (offset >= data.size())
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return Error::from_string_literal("Unexpected EOF when parsing name");
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size_t dummy = (b & 0x3f) << 8 | data[offset++];
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auto rest_of_name = TRY(parse(data, dummy, recursion_level + 1));
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builder.append(rest_of_name.as_string());
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if (builder.length() > MAX_NAME_SIZE)
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return Error::from_string_literal("Domain name exceeds maximum allowed length");
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return builder.to_deprecated_string();
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} else {
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// This is the length of a part.
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if (offset + b >= data.size())
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return Error::from_string_literal("Unexpected EOF when parsing name");
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if (b > MAX_LABEL_SIZE)
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return Error::from_string_literal("DNS label exceeds maximum allowed length");
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builder.append({ data.offset_pointer(offset), b });
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builder.append('.');
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if (builder.length() > MAX_NAME_SIZE)
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return Error::from_string_literal("Domain name exceeds maximum allowed length");
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offset += b;
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}
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}
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}
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size_t Name::serialized_size() const
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{
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if (m_name.is_empty())
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return 1;
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return m_name.length() + 2;
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}
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void Name::randomize_case()
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{
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StringBuilder builder;
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for (char c : m_name) {
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// Randomize the 0x20 bit in every ASCII character.
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if (isalpha(c)) {
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if (get_random_uniform(2))
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c |= 0x20;
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else
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c &= ~0x20;
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}
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builder.append(c);
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}
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m_name = builder.to_deprecated_string();
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}
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ErrorOr<void> Name::write_to_stream(Stream& stream) const
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{
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auto parts = as_string().split_view('.');
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for (auto& part : parts) {
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TRY(stream.write_value<u8>(part.length()));
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TRY(stream.write_until_depleted(part.bytes()));
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}
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TRY(stream.write_value('\0'));
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return {};
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}
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unsigned Name::Traits::hash(Name const& name)
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{
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return CaseInsensitiveStringTraits::hash(name.as_string());
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}
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bool Name::Traits::equals(Name const& a, Name const& b)
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{
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return CaseInsensitiveStringTraits::equals(a.as_string(), b.as_string());
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}
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}
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