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Add new private method QPDF::processXRefSize

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This commit is contained in:
m-holger 2024-05-22 15:36:45 +01:00
parent f74b28f0d1
commit 7477ea7828
2 changed files with 41 additions and 20 deletions
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8
include/qpdf/QPDF.hh
View File

@ -1028,11 +1028,13 @@ class QPDF
qpdf_offset_t read_xrefTable(qpdf_offset_t offset);
qpdf_offset_t read_xrefStream(qpdf_offset_t offset);
qpdf_offset_t processXRefStream(qpdf_offset_t offset, QPDFObjectHandle& xref_stream);
std::pair<size_t, std::array<int, 3>>
std::pair<int, std::array<int, 3>>
processXRefW(QPDFObjectHandle& dict, std::function<QPDFExc(std::string_view)> damaged);
std::pair<size_t, std::vector<long long>> processXRefIndex(
int processXRefSize(
QPDFObjectHandle& dict, int entry_size, std::function<QPDFExc(std::string_view)> damaged);
std::pair<int, std::vector<long long>> processXRefIndex(
QPDFObjectHandle& dict,
size_t entry_size,
int max_num_entries,
std::function<QPDFExc(std::string_view)> damaged);
void insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2);
void insertFreeXrefEntry(QPDFObjGen);

53
libqpdf/QPDF.cc
View File

@ -969,7 +969,7 @@ QPDF::read_xrefStream(qpdf_offset_t xref_offset)
}
// Return the entry size of the xref stream and the processed W array.
std::pair<size_t, std::array<int, 3>>
std::pair<int, std::array<int, 3>>
QPDF::processXRefW(QPDFObjectHandle& dict, std::function<QPDFExc(std::string_view)> damaged)
{
auto W_obj = dict.getKey("/W");
@ -995,17 +995,39 @@ QPDF::processXRefW(QPDFObjectHandle& dict, std::function<QPDFExc(std::string_vie
if (entry_size == 0) {
throw damaged("Cross-reference stream's /W indicates entry size of 0");
}
return {toS(entry_size), W};
return {entry_size, W};
}
// Return the expected size of the xref stream and the processed Index array.
std::pair<size_t, std::vector<long long>>
QPDF::processXRefIndex(
QPDFObjectHandle& dict, size_t entry_size, std::function<QPDFExc(std::string_view)> damaged)
// Validate Size key and return the maximum number of entries that the xref stream can contain.
int
QPDF::processXRefSize(
QPDFObjectHandle& dict, int entry_size, std::function<QPDFExc(std::string_view)> damaged)
{
auto max_num_entries = static_cast<unsigned long long>(-1) / entry_size;
// Number of entries is limited by the highest possible object id and stream size.
auto max_num_entries = std::numeric_limits<int>::max();
if (max_num_entries > (std::numeric_limits<qpdf_offset_t>::max() / entry_size)) {
max_num_entries = toI(std::numeric_limits<qpdf_offset_t>::max() / entry_size);
}
auto Size_obj = dict.getKey("/Size");
long long size;
if (!dict.getKey("/Size").getValueAsInt(size)) {
throw damaged("Cross-reference stream does not have a proper /Size key");
} else if (size < 0) {
throw damaged("Cross-reference stream has a negative /Size key");
} else if (size >= max_num_entries) {
throw damaged("Cross-reference stream has an impossibly large /Size key");
}
// We are not validating that Size <= (Size key of parent xref / trailer).
return max_num_entries;
}
// Return the number of entries of the xref stream and the processed Index array.
std::pair<int, std::vector<long long>>
QPDF::processXRefIndex(
QPDFObjectHandle& dict, int max_num_entries, std::function<QPDFExc(std::string_view)> damaged)
{
auto size = dict.getKey("/Size").getIntValueAsInt();
auto Index_obj = dict.getKey("/Index");
if (!(Index_obj.isArray() || Index_obj.isNull())) {
throw damaged("Cross-reference stream does not have a proper /Index key");
@ -1030,29 +1052,28 @@ QPDF::processXRefIndex(
} else {
// We have already validated the /Index key.
QTC::TC("qpdf", "QPDF xref /Index is null");
long long size = Size_obj.getIntValue();
indx.push_back(0);
indx.push_back(size);
}
size_t num_entries = 0;
int num_entries = 0;
for (size_t i = 1; i < indx.size(); i += 2) {
// We are guarding against the possibility of num_entries * entry_size overflowing.
// We are not checking that entries are in ascending order as required by the spec, which
// probably should generate a warning. We are also not checking that for each subsection
// first object number + number of entries <= /Size. The spec requires us to ignore object
// number > /Size.
if (indx.at(i) > QIntC::to_longlong(max_num_entries - num_entries)) {
if (indx.at(i) > (max_num_entries - num_entries)) {
throw damaged(
"Cross-reference stream claims to contain too many entries: " +
std::to_string(indx.at(i)) + " " + std::to_string(max_num_entries) + " " +
std::to_string(num_entries));
}
num_entries += toS(indx.at(i));
num_entries += indx.at(i);
}
// entry_size and num_entries have both been validated to ensure that this multiplication does
// not cause an overflow.
return {entry_size * num_entries, indx};
return {num_entries, indx};
}
qpdf_offset_t
@ -1063,16 +1084,14 @@ QPDF::processXRefStream(qpdf_offset_t xref_offset, QPDFObjectHandle& xref_obj)
};
auto dict = xref_obj.getDict();
auto Size_obj = dict.getKey("/Size");
if (!Size_obj.isInteger()) {
throw damaged("Cross-reference stream does not have a proper /Size key");
}
auto [entry_size, W] = processXRefW(dict, damaged);
auto [expected_size, indx] = processXRefIndex(dict, entry_size, damaged);
int max_num_entries = processXRefSize(dict, entry_size, damaged);
auto [num_entries, indx] = processXRefIndex(dict, max_num_entries, damaged);
std::shared_ptr<Buffer> bp = xref_obj.getStreamData(qpdf_dl_specialized);
size_t actual_size = bp->getSize();
auto expected_size = toS(entry_size) * toS(num_entries);
if (expected_size != actual_size) {
QPDFExc x = damaged(