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Refactor QPDF::Xref_table::read_entry and read_bad_entry

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Return results rather than using reference parameters.

Fixes bug in #1272 where parameters were not reinitialized when calling
read_bad_entry from read_entry.
This commit is contained in:
m-holger 2024-09-20 13:58:47 +01:00
parent 06a2d955fc
commit 44a1395194
2 changed files with 30 additions and 28 deletions
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54
libqpdf/QPDF.cc
View File

@ -832,10 +832,6 @@ std::vector<QPDF::Xref_table::Subsection>
QPDF::Xref_table::bad_subsections(std::string& line, qpdf_offset_t start)
{
std::vector<QPDF::Xref_table::Subsection> result;
qpdf_offset_t f1 = 0;
int f2 = 0;
char type = '\0';
file->seek(start, SEEK_SET);
while (true) {
@ -844,7 +840,7 @@ QPDF::Xref_table::bad_subsections(std::string& line, qpdf_offset_t start)
auto [obj, num, offset] = result.emplace_back(subsection(line));
file->seek(offset, SEEK_SET);
for (qpdf_offset_t i = obj; i - num < obj; ++i) {
if (!read_entry(f1, f2, type)) {
if (!std::get<0>(read_entry())) {
QTC::TC("qpdf", "QPDF invalid xref entry");
throw damaged_table("invalid xref entry (obj=" + std::to_string(i) + ")");
}
@ -890,9 +886,13 @@ QPDF::Xref_table::subsections(std::string& line)
}
}
bool
QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
// Returns (success, f1, f2, type).
std::tuple<bool, qpdf_offset_t, int, char>
QPDF::Xref_table::read_bad_entry()
{
qpdf_offset_t f1{0};
int f2{0};
char type{'\0'};
// Reposition after initial read attempt and reread.
file->seek(file->getLastOffset(), SEEK_SET);
auto line = file->readLine(30);
@ -910,7 +910,7 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
}
// Require digit
if (!QUtil::is_digit(*p)) {
return false;
return {false, 0, 0, '\0'};
}
// Gather digits
std::string f1_str;
@ -919,7 +919,7 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
}
// Require space
if (!QUtil::is_space(*p)) {
return false;
return {false, 0, 0, '\0'};
}
if (QUtil::is_space(*(p + 1))) {
QTC::TC("qpdf", "QPDF ignore first extra space in xref entry");
@ -931,7 +931,7 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
}
// Require digit
if (!QUtil::is_digit(*p)) {
return false;
return {false, 0, 0, '\0'};
}
// Gather digits
std::string f2_str;
@ -940,7 +940,7 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
}
// Require space
if (!QUtil::is_space(*p)) {
return false;
return {false, 0, 0, '\0'};
}
if (QUtil::is_space(*(p + 1))) {
QTC::TC("qpdf", "QPDF ignore second extra space in xref entry");
@ -953,7 +953,7 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
if ((*p == 'f') || (*p == 'n')) {
type = *p;
} else {
return false;
return {false, 0, 0, '\0'};
}
if ((f1_str.length() != 10) || (f2_str.length() != 5)) {
QTC::TC("qpdf", "QPDF ignore length error xref entry");
@ -967,18 +967,23 @@ QPDF::Xref_table::read_bad_entry(qpdf_offset_t& f1, int& f2, char& type)
f1 = QUtil::string_to_ll(f1_str.c_str());
f2 = QUtil::string_to_int(f2_str.c_str());
return true;
return {true, f1, f2, type};
}
// Optimistically read and parse xref entry. If entry is bad, call read_bad_xrefEntry and return
// result.
bool
QPDF::Xref_table::read_entry(qpdf_offset_t& f1, int& f2, char& type)
// result. Returns (success, f1, f2, type).
std::tuple<bool, qpdf_offset_t, int, char>
QPDF::Xref_table::read_entry()
{
qpdf_offset_t f1{0};
int f2{0};
char type{'\0'};
std::array<char, 21> line;
f1 = 0;
f2 = 0;
if (file->read(line.data(), 20) != 20) {
// C++20: [[unlikely]]
return false;
return {false, 0, 0, '\0'};
}
line[20] = '\0';
char const* p = line.data();
@ -1002,7 +1007,7 @@ QPDF::Xref_table::read_entry(qpdf_offset_t& f1, int& f2, char& type)
if (!QUtil::is_space(*p++)) {
// Entry doesn't start with space or digit.
// C++20: [[unlikely]]
return false;
return {false, 0, 0, '\0'};
}
// Gather digits. NB No risk of overflow as 99'999 < max int.
while (*p == '0') {
@ -1019,10 +1024,10 @@ QPDF::Xref_table::read_entry(qpdf_offset_t& f1, int& f2, char& type)
// No test for valid line[19].
if (*(++p) && *(++p) && (*p == '\n' || *p == '\r') && f1_len == 10 && f2_len == 5) {
// C++20: [[likely]]
return true;
return {true, f1, f2, type};
}
}
return read_bad_entry(f1, f2, type);
return read_bad_entry();
}
// Read a single cross-reference table section and associated trailer.
@ -1064,10 +1069,8 @@ QPDF::Xref_table::process_section(qpdf_offset_t xref_offset)
first_item_offset_ = file->tell();
}
// For xref_table, these will always be small enough to be ints
qpdf_offset_t f1 = 0;
int f2 = 0;
char type = '\0';
if (!read_entry(f1, f2, type)) {
auto [success, f1, f2, type] = read_entry();
if (!success) {
throw damaged_table("invalid xref entry (obj=" + std::to_string(i) + ")");
}
if (type == 'f') {
@ -1585,8 +1588,7 @@ QPDF::Xref_table::read_trailer()
{
qpdf_offset_t offset = file->tell();
bool empty = false;
auto object =
QPDFParser(*file, "trailer", tokenizer, nullptr, &qpdf, true).parse(empty, false);
auto object = QPDFParser(*file, "trailer", tokenizer, nullptr, &qpdf, true).parse(empty, false);
if (empty) {
// Nothing in the PDF spec appears to allow empty objects, but they have been encountered in
// actual PDF files and Adobe Reader appears to ignore them.

4
libqpdf/qpdf/QPDF_private.hh
View File

@ -292,8 +292,8 @@ class QPDF::Xref_table
std::vector<Subsection> subsections(std::string& line);
std::vector<Subsection> bad_subsections(std::string& line, qpdf_offset_t offset);
Subsection subsection(std::string const& line);
bool read_entry(qpdf_offset_t& f1, int& f2, char& type);
bool read_bad_entry(qpdf_offset_t& f1, int& f2, char& type);
std::tuple<bool, qpdf_offset_t, int, char> read_entry();
std::tuple<bool, qpdf_offset_t, int, char> read_bad_entry();
// Methods to parse streams
qpdf_offset_t read_stream(qpdf_offset_t offset);