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LibCrypto: Restore cached tag when a failed ASN1 read is rolled back

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Previously, the stack would be restored to its previous position but
the tag would retain its old value, leading to an inconsistent state.
This commit is contained in:
Tim Ledbetter 2026-06-05 12:55:20 +01:00 committed by Tim Ledbetter
parent a8d729ff9c
commit ed6aec8dfa
2 changed files with 32 additions and 0 deletions
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8
Libraries/LibCrypto/ASN1/DER.h
View file

@ -157,16 +157,19 @@ public:
return Error::from_string_literal("ASN1::Decoder: Trying to drop using a decoder that is EOF");
auto previous_position = m_stack;
auto previous_tag = m_current_tag;
auto tag_or_error = peek();
if (tag_or_error.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return tag_or_error.release_error();
}
auto length_or_error = read_length();
if (length_or_error.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return length_or_error.release_error();
}
@ -175,6 +178,7 @@ public:
auto bytes_result = read_bytes(length);
if (bytes_result.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return bytes_result.release_error();
}
@ -192,16 +196,19 @@ public:
return Error::from_string_literal("ASN1::Decoder: Trying to read using a decoder that is EOF");
auto previous_position = m_stack;
auto previous_tag = m_current_tag;
auto tag_or_error = peek();
if (tag_or_error.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return tag_or_error.release_error();
}
auto length_or_error = read_length();
if (length_or_error.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return length_or_error.release_error();
}
@ -211,6 +218,7 @@ public:
auto value_or_error = read_value<ValueType>(class_override.value_or(tag.class_), kind_override.value_or(tag.kind), length);
if (value_or_error.is_error()) {
m_stack = move(previous_position);
m_current_tag = move(previous_tag);
return value_or_error.release_error();
}

24
Tests/LibCrypto/TestASN1.cpp
View file

@ -238,3 +238,27 @@ TEST_CASE(test_encoder_constructed)
MUST(decoder.leave()); // Sequence
EXPECT(decoder.eof()); // no other data
}
TEST_CASE(test_decoder_restores_state_after_failed_read)
{
// A Boolean tag declaring a length of 5, but only 3 value bytes are present.
u8 const data[] { 0x01, 0x05, 0x00, 0x00, 0x00 };
Crypto::ASN1::Decoder decoder({ data, sizeof(data) });
EXPECT(decoder.read<bool>().is_error());
// The first failed read should leave the decoder state unchanged, so a second drop should have the same result.
EXPECT(decoder.read<bool>().is_error());
}
TEST_CASE(test_decoder_restores_state_after_failed_drop)
{
// A Boolean tag declaring a length of 5, but only 3 value bytes are present.
u8 const data[] { 0x01, 0x05, 0x00, 0x00, 0x00 };
Crypto::ASN1::Decoder decoder({ data, sizeof(data) });
EXPECT(decoder.drop().is_error());
// The first failed drop should leave the decoder state unchanged, so a second drop should have the same result.
EXPECT(decoder.drop().is_error());
}