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/*
* BER Decoder
* (C) 1999-2008,2015,2017,2018 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/
#include <botan/ber_dec.h>
#include <botan/bigint.h>
#include <botan/loadstor.h>
#include <botan/internal/safeint.h>
namespace Botan {
namespace {
/*
* This value is somewhat arbitrary. OpenSSL allows up to 128 nested
* indefinite length sequences. If you increase this, also increase the
* limit in the test in test_asn1.cpp
*/
const size_t ALLOWED_EOC_NESTINGS = 16;
/*
* BER decode an ASN.1 type tag
*/
size_t decode_tag(DataSource* ber, ASN1_Tag& type_tag, ASN1_Tag& class_tag)
{
uint8_t b;
if(!ber->read_byte(b))
{
class_tag = type_tag = NO_OBJECT;
return 0;
}
if((b & 0x1F) != 0x1F)
{
type_tag = ASN1_Tag(b & 0x1F);
class_tag = ASN1_Tag(b & 0xE0);
return 1;
}
size_t tag_bytes = 1;
class_tag = ASN1_Tag(b & 0xE0);
size_t tag_buf = 0;
while(true)
{
if(!ber->read_byte(b))
throw BER_Decoding_Error("Long-form tag truncated");
if(tag_buf & 0xFF000000)
throw BER_Decoding_Error("Long-form tag overflowed 32 bits");
++tag_bytes;
tag_buf = (tag_buf << 7) | (b & 0x7F);
if((b & 0x80) == 0) break;
}
type_tag = ASN1_Tag(tag_buf);
return tag_bytes;
}
/*
* Find the EOC marker
*/
size_t find_eoc(DataSource* src, size_t allow_indef);
/*
* BER decode an ASN.1 length field
*/
size_t decode_length(DataSource* ber, size_t& field_size, size_t allow_indef)
{
uint8_t b;
if(!ber->read_byte(b))
throw BER_Decoding_Error("Length field not found");
field_size = 1;
if((b & 0x80) == 0)
return b;
field_size += (b & 0x7F);
if(field_size > 5)
throw BER_Decoding_Error("Length field is too large");
if(field_size == 1)
{
if(allow_indef == 0)
{
throw BER_Decoding_Error("Nested EOC markers too deep, rejecting to avoid stack exhaustion");
}
else
{
return find_eoc(ber, allow_indef - 1);
}
}
size_t length = 0;
for(size_t i = 0; i != field_size - 1; ++i)
{
if(get_byte(0, length) != 0)
throw BER_Decoding_Error("Field length overflow");
if(!ber->read_byte(b))
throw BER_Decoding_Error("Corrupted length field");
length = (length << 8) | b;
}
return length;
}
/*
* Find the EOC marker
*/
size_t find_eoc(DataSource* ber, size_t allow_indef)
{
secure_vector<uint8_t> buffer(BOTAN_DEFAULT_BUFFER_SIZE), data;
while(true)
{
const size_t got = ber->peek(buffer.data(), buffer.size(), data.size());
if(got == 0)
break;
data += std::make_pair(buffer.data(), got);
}
DataSource_Memory source(data);
data.clear();
size_t length = 0;
while(true)
{
ASN1_Tag type_tag, class_tag;
size_t tag_size = decode_tag(&source, type_tag, class_tag);
if(type_tag == NO_OBJECT)
break;
size_t length_size = 0;
size_t item_size = decode_length(&source, length_size, allow_indef);
source.discard_next(item_size);
length = BOTAN_CHECKED_ADD(length, item_size);
length = BOTAN_CHECKED_ADD(length, tag_size);
length = BOTAN_CHECKED_ADD(length, length_size);
if(type_tag == EOC && class_tag == UNIVERSAL)
break;
}
return length;
}
class DataSource_BERObject final : public DataSource
{
public:
size_t read(uint8_t out[], size_t length) override
{
BOTAN_ASSERT_NOMSG(m_offset <= m_obj.length());
const size_t got = std::min<size_t>(m_obj.length() - m_offset, length);
copy_mem(out, m_obj.bits() + m_offset, got);
m_offset += got;
return got;
}
size_t peek(uint8_t out[], size_t length, size_t peek_offset) const override
{
BOTAN_ASSERT_NOMSG(m_offset <= m_obj.length());
const size_t bytes_left = m_obj.length() - m_offset;
if(peek_offset >= bytes_left)
return 0;
const size_t got = std::min(bytes_left - peek_offset, length);
copy_mem(out, m_obj.bits() + peek_offset, got);
return got;
}
bool check_available(size_t n) override
{
BOTAN_ASSERT_NOMSG(m_offset <= m_obj.length());
return (n <= (m_obj.length() - m_offset));
}
bool end_of_data() const override
{
return get_bytes_read() == m_obj.length();
}
size_t get_bytes_read() const override { return m_offset; }
explicit DataSource_BERObject(BER_Object&& obj) : m_obj(std::move(obj)), m_offset(0) {}
private:
BER_Object m_obj;
size_t m_offset;
};
}
/*
* Check if more objects are there
*/
bool BER_Decoder::more_items() const
{
if(m_source->end_of_data() && !m_pushed.is_set())
return false;
return true;
}
/*
* Verify that no bytes remain in the source
*/
BER_Decoder& BER_Decoder::verify_end()
{
return verify_end("BER_Decoder::verify_end called, but data remains");
}
/*
* Verify that no bytes remain in the source
*/
BER_Decoder& BER_Decoder::verify_end(const std::string& err)
{
if(!m_source->end_of_data() || m_pushed.is_set())
throw Decoding_Error(err);
return (*this);
}
/*
* Discard all the bytes remaining in the source
*/
BER_Decoder& BER_Decoder::discard_remaining()
{
uint8_t buf;
while(m_source->read_byte(buf))
{}
return (*this);
}
/*
* Return the BER encoding of the next object
*/
BER_Object BER_Decoder::get_next_object()
{
BER_Object next;
if(m_pushed.is_set())
{
std::swap(next, m_pushed);
return next;
}
for(;;)
{
ASN1_Tag type_tag, class_tag;
decode_tag(m_source, type_tag, class_tag);
next.set_tagging(type_tag, class_tag);
if(next.is_set() == false) // no more objects
return next;
size_t field_size;
const size_t length = decode_length(m_source, field_size, ALLOWED_EOC_NESTINGS);
if(!m_source->check_available(length))
throw BER_Decoding_Error("Value truncated");
uint8_t* out = next.mutable_bits(length);
if(m_source->read(out, length) != length)
throw BER_Decoding_Error("Value truncated");
if(next.tagging() == EOC)
continue;
else
break;
}
return next;
}
/*
* Push a object back into the stream
*/
void BER_Decoder::push_back(const BER_Object& obj)
{
if(m_pushed.is_set())
throw Invalid_State("BER_Decoder: Only one push back is allowed");
m_pushed = obj;
}
void BER_Decoder::push_back(BER_Object&& obj)
{
if(m_pushed.is_set())
throw Invalid_State("BER_Decoder: Only one push back is allowed");
m_pushed = std::move(obj);
}
BER_Decoder BER_Decoder::start_cons(ASN1_Tag type_tag, ASN1_Tag class_tag)
{
BER_Object obj = get_next_object();
obj.assert_is_a(type_tag, ASN1_Tag(class_tag | CONSTRUCTED));
return BER_Decoder(std::move(obj), this);
}
/*
* Finish decoding a CONSTRUCTED type
*/
BER_Decoder& BER_Decoder::end_cons()
{
if(!m_parent)
throw Invalid_State("BER_Decoder::end_cons called with null parent");
if(!m_source->end_of_data())
throw Decoding_Error("BER_Decoder::end_cons called with data left");
return (*m_parent);
}
BER_Decoder::BER_Decoder(BER_Object&& obj, BER_Decoder* parent)
{
m_data_src.reset(new DataSource_BERObject(std::move(obj)));
m_source = m_data_src.get();
m_parent = parent;
}
/*
* BER_Decoder Constructor
*/
BER_Decoder::BER_Decoder(DataSource& src)
{
m_source = &src;
}
/*
* BER_Decoder Constructor
*/
BER_Decoder::BER_Decoder(const uint8_t data[], size_t length)
{
m_data_src.reset(new DataSource_Memory(data, length));
m_source = m_data_src.get();
}
/*
* BER_Decoder Constructor
*/
BER_Decoder::BER_Decoder(const secure_vector<uint8_t>& data)
{
m_data_src.reset(new DataSource_Memory(data));
m_source = m_data_src.get();
}
/*
* BER_Decoder Constructor
*/
BER_Decoder::BER_Decoder(const std::vector<uint8_t>& data)
{
m_data_src.reset(new DataSource_Memory(data.data(), data.size()));
m_source = m_data_src.get();
}
/*
* BER_Decoder Copy Constructor
*/
BER_Decoder::BER_Decoder(const BER_Decoder& other)
{
m_source = other.m_source;
// take ownership
std::swap(m_data_src, other.m_data_src);
m_parent = other.m_parent;
}
/*
* Request for an object to decode itself
*/
BER_Decoder& BER_Decoder::decode(ASN1_Object& obj,
ASN1_Tag, ASN1_Tag)
{
obj.decode_from(*this);
return (*this);
}
/*
* Decode a BER encoded NULL
*/
BER_Decoder& BER_Decoder::decode_null()
{
BER_Object obj = get_next_object();
obj.assert_is_a(NULL_TAG, UNIVERSAL);
if(obj.length() > 0)
throw BER_Decoding_Error("NULL object had nonzero size");
return (*this);
}
BER_Decoder& BER_Decoder::decode_octet_string_bigint(BigInt& out)
{
secure_vector<uint8_t> out_vec;
decode(out_vec, OCTET_STRING);
out = BigInt::decode(out_vec.data(), out_vec.size());
return (*this);
}
/*
* Decode a BER encoded BOOLEAN
*/
BER_Decoder& BER_Decoder::decode(bool& out,
ASN1_Tag type_tag, ASN1_Tag class_tag)
{
BER_Object obj = get_next_object();
obj.assert_is_a(type_tag, class_tag);
if(obj.length() != 1)
throw BER_Decoding_Error("BER boolean value had invalid size");
out = (obj.bits()[0]) ? true : false;
return (*this);
}
/*
* Decode a small BER encoded INTEGER
*/
BER_Decoder& BER_Decoder::decode(size_t& out,
ASN1_Tag type_tag,
ASN1_Tag class_tag)
{
BigInt integer;
decode(integer, type_tag, class_tag);
if(integer.is_negative())
throw BER_Decoding_Error("Decoded small integer value was negative");
if(integer.bits() > 32)
throw BER_Decoding_Error("Decoded integer value larger than expected");
out = 0;
for(size_t i = 0; i != 4; ++i)
out = (out << 8) | integer.byte_at(3-i);
return (*this);
}
/*
* Decode a small BER encoded INTEGER
*/
uint64_t BER_Decoder::decode_constrained_integer(ASN1_Tag type_tag,
ASN1_Tag class_tag,
size_t T_bytes)
{
if(T_bytes > 8)
throw BER_Decoding_Error("Can't decode small integer over 8 bytes");
BigInt integer;
decode(integer, type_tag, class_tag);
if(integer.bits() > 8*T_bytes)
throw BER_Decoding_Error("Decoded integer value larger than expected");
uint64_t out = 0;
for(size_t i = 0; i != 8; ++i)
out = (out << 8) | integer.byte_at(7-i);
return out;
}
/*
* Decode a BER encoded INTEGER
*/
BER_Decoder& BER_Decoder::decode(BigInt& out,
ASN1_Tag type_tag,
ASN1_Tag class_tag)
{
BER_Object obj = get_next_object();
obj.assert_is_a(type_tag, class_tag);
if(obj.length() == 0)
{
out = 0;
}
else
{
const bool negative = (obj.bits()[0] & 0x80) ? true : false;
if(negative)
{
secure_vector<uint8_t> vec(obj.bits(), obj.bits() + obj.length());
for(size_t i = obj.length(); i > 0; --i)
if(vec[i-1]--)
break;
for(size_t i = 0; i != obj.length(); ++i)
vec[i] = ~vec[i];
out = BigInt(vec.data(), vec.size());
out.flip_sign();
}
else
{
out = BigInt(obj.bits(), obj.length());
}
}
return (*this);
}
namespace {
template<typename Alloc>
void asn1_decode_binary_string(std::vector<uint8_t, Alloc>& buffer,
const BER_Object& obj,
ASN1_Tag real_type,
ASN1_Tag type_tag,
ASN1_Tag class_tag)
{
obj.assert_is_a(type_tag, class_tag);
if(real_type == OCTET_STRING)
{
buffer.assign(obj.bits(), obj.bits() + obj.length());
}
else
{
if(obj.length() == 0)
throw BER_Decoding_Error("Invalid BIT STRING");
if(obj.bits()[0] >= 8)
throw BER_Decoding_Error("Bad number of unused bits in BIT STRING");
buffer.resize(obj.length() - 1);
if(obj.length() > 1)
copy_mem(buffer.data(), obj.bits() + 1, obj.length() - 1);
}
}
}
/*
* BER decode a BIT STRING or OCTET STRING
*/
BER_Decoder& BER_Decoder::decode(secure_vector<uint8_t>& buffer,
ASN1_Tag real_type,
ASN1_Tag type_tag, ASN1_Tag class_tag)
{
if(real_type != OCTET_STRING && real_type != BIT_STRING)
throw BER_Bad_Tag("Bad tag for {BIT,OCTET} STRING", real_type);
asn1_decode_binary_string(buffer, get_next_object(), real_type, type_tag, class_tag);
return (*this);
}
BER_Decoder& BER_Decoder::decode(std::vector<uint8_t>& buffer,
ASN1_Tag real_type,
ASN1_Tag type_tag, ASN1_Tag class_tag)
{
if(real_type != OCTET_STRING && real_type != BIT_STRING)
throw BER_Bad_Tag("Bad tag for {BIT,OCTET} STRING", real_type);
asn1_decode_binary_string(buffer, get_next_object(), real_type, type_tag, class_tag);
return (*this);
}
}