mirror of
https://github.com/qpdf/qpdf.git
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d71f05ca07
This makes all integer type conversions that have potential data loss explicit with calls that do range checks and raise an exception. After this commit, qpdf builds with no warnings when -Wsign-conversion -Wconversion is used with gcc or clang or when -W3 -Wd4800 is used with MSVC. This significantly reduces the likelihood of potential crashes from bogus integer values. There are some parts of the code that take int when they should take size_t or an offset. Such places would make qpdf not support files with more than 2^31 of something that usually wouldn't be so large. In the event that such a file shows up and is valid, at least qpdf would raise an error in the right spot so the issue could be legitimately addressed rather than failing in some weird way because of a silent overflow condition.
249 lines
5.5 KiB
C++
249 lines
5.5 KiB
C++
#include <qpdf/Pl_LZWDecoder.hh>
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#include <qpdf/QTC.hh>
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#include <qpdf/QUtil.hh>
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#include <qpdf/QIntC.hh>
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#include <stdexcept>
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#include <string.h>
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#include <assert.h>
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Pl_LZWDecoder::Pl_LZWDecoder(char const* identifier, Pipeline* next,
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bool early_code_change) :
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Pipeline(identifier, next),
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code_size(9),
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next(0),
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byte_pos(0),
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bit_pos(0),
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bits_available(0),
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code_change_delta(early_code_change ? 1 : 0),
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eod(false),
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last_code(256)
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{
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memset(buf, 0, 3);
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}
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Pl_LZWDecoder::~Pl_LZWDecoder()
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{
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}
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void
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Pl_LZWDecoder::write(unsigned char* bytes, size_t len)
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{
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for (size_t i = 0; i < len; ++i)
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{
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this->buf[next++] = bytes[i];
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if (this->next == 3)
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{
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this->next = 0;
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}
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this->bits_available += 8;
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if (this->bits_available >= this->code_size)
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{
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sendNextCode();
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}
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}
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}
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void
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Pl_LZWDecoder::finish()
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{
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getNext()->finish();
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}
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void
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Pl_LZWDecoder::sendNextCode()
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{
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unsigned int high = this->byte_pos;
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unsigned int med = (this->byte_pos + 1) % 3;
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unsigned int low = (this->byte_pos + 2) % 3;
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unsigned int bits_from_high = 8 - this->bit_pos;
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unsigned int bits_from_med = this->code_size - bits_from_high;
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unsigned int bits_from_low = 0;
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if (bits_from_med > 8)
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{
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bits_from_low = bits_from_med - 8;
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bits_from_med = 8;
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}
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unsigned int high_mask = (1U << bits_from_high) - 1U;
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unsigned int med_mask = 0xff - ((1U << (8 - bits_from_med)) - 1U);
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unsigned int low_mask = 0xff - ((1U << (8 - bits_from_low)) - 1U);
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unsigned int code = 0;
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code += (this->buf[high] & high_mask) << bits_from_med;
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code += ((this->buf[med] & med_mask) >> (8 - bits_from_med));
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if (bits_from_low)
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{
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code <<= bits_from_low;
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code += ((this->buf[low] & low_mask) >> (8 - bits_from_low));
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this->byte_pos = low;
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this->bit_pos = bits_from_low;
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}
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else
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{
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this->byte_pos = med;
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this->bit_pos = bits_from_med;
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}
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if (this->bit_pos == 8)
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{
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this->bit_pos = 0;
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++this->byte_pos;
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this->byte_pos %= 3;
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}
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this->bits_available -= this->code_size;
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handleCode(code);
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}
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unsigned char
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Pl_LZWDecoder::getFirstChar(unsigned int code)
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{
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unsigned char result = '\0';
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if (code < 256)
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{
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result = static_cast<unsigned char>(code);
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}
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else if (code > 257)
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{
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unsigned int idx = code - 258;
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if (idx >= table.size())
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{
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throw std::logic_error(
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"Pl_LZWDecoder::getFirstChar: table overflow");
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}
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Buffer& b = table.at(idx);
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result = b.getBuffer()[0];
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}
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else
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{
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throw std::logic_error(
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"Pl_LZWDecoder::getFirstChar called with invalid code (" +
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QUtil::int_to_string(code) + ")");
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}
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return result;
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}
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void
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Pl_LZWDecoder::addToTable(unsigned char next)
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{
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unsigned int last_size = 0;
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unsigned char const* last_data = 0;
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unsigned char tmp[1];
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if (this->last_code < 256)
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{
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tmp[0] = static_cast<unsigned char>(this->last_code);
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last_data = tmp;
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last_size = 1;
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}
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else if (this->last_code > 257)
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{
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unsigned int idx = this->last_code - 258;
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if (idx >= table.size())
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{
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throw std::logic_error(
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"Pl_LZWDecoder::addToTable: table overflow");
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}
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Buffer& b = table.at(idx);
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last_data = b.getBuffer();
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last_size = QIntC::to_uint(b.getSize());
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}
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else
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{
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throw std::logic_error(
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"Pl_LZWDecoder::addToTable called with invalid code (" +
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QUtil::int_to_string(this->last_code) + ")");
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}
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Buffer entry(1 + last_size);
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unsigned char* new_data = entry.getBuffer();
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memcpy(new_data, last_data, last_size);
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new_data[last_size] = next;
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this->table.push_back(entry);
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}
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void
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Pl_LZWDecoder::handleCode(unsigned int code)
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{
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if (this->eod)
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{
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return;
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}
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if (code == 256)
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{
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if (! this->table.empty())
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{
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QTC::TC("libtests", "Pl_LZWDecoder intermediate reset");
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}
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this->table.clear();
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this->code_size = 9;
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}
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else if (code == 257)
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{
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this->eod = true;
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}
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else
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{
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if (this->last_code != 256)
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{
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// Add to the table from last time. New table entry would
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// be what we read last plus the first character of what
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// we're reading now.
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unsigned char next = '\0';
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unsigned int table_size = QIntC::to_uint(table.size());
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if (code < 256)
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{
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// just read < 256; last time's next was code
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next = static_cast<unsigned char>(code);
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}
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else if (code > 257)
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{
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size_t idx = code - 258;
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if (idx > table_size)
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{
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throw std::runtime_error("LZWDecoder: bad code received");
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}
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else if (idx == table_size)
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{
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// The encoder would have just created this entry,
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// so the first character of this entry would have
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// been the same as the first character of the
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// last entry.
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QTC::TC("libtests", "Pl_LZWDecoder last was table size");
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next = getFirstChar(this->last_code);
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}
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else
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{
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next = getFirstChar(code);
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}
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}
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unsigned int new_idx = 258 + table_size;
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if (new_idx == 4096)
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{
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throw std::runtime_error("LZWDecoder: table full");
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}
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addToTable(next);
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unsigned int change_idx = new_idx + code_change_delta;
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if ((change_idx == 511) ||
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(change_idx == 1023) ||
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(change_idx == 2047))
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{
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++this->code_size;
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}
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}
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if (code < 256)
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{
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unsigned char ch = static_cast<unsigned char>(code);
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getNext()->write(&ch, 1);
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}
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else
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{
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Buffer& b = table.at(code - 258);
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getNext()->write(b.getBuffer(), b.getSize());
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}
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}
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this->last_code = code;
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}
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