Add additional object id sanity checks

Ensure objects with impossibly large ids are ignored.

Add additional object id sanity checks
Ensure objects with impossibly large ids are ignored.
m-holger
1 parent 42c51119
Showing 5 changed files with 37 additions and 10 deletions
include/qpdf/QPDF.hh
libqpdf/QPDF.cc
qpdf/qtest/qpdf/issue-118.out
qpdf/qtest/qpdf/issue-120.out
qpdf/qtest/qpdf/issue-143.out
@@ -1502,6 +1502,9 @@ class QPDF
         std::shared_ptr<EncryptionParameters> encp;
         std::string pdf_version;
         std::map<QPDFObjGen, QPDFXRefEntry> xref_table;
+        // Various tables are indexed by object id, with potential size id + 1
+        int xref_table_max_id{std::numeric_limits<int>::max() - 1};
+        qpdf_offset_t xref_table_max_offset{0};
         std::set<int> deleted_objects;
         std::map<QPDFObjGen, ObjCache> obj_cache;
         std::set<QPDFObjGen> resolving;
@@ -441,6 +441,12 @@ QPDF::parse(char const* password)
     // 30 characters to leave room for the startxref stuff.
     m->file->seek(0, SEEK_END);
     qpdf_offset_t end_offset = m->file->tell();
+    m->xref_table_max_offset = end_offset;
+    // Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
+    // scenarios at least 3 bytes are required.
+    if (m->xref_table_max_id > m->xref_table_max_offset / 3) {
+        m->xref_table_max_id = static_cast<int>(m->xref_table_max_offset / 3);
+    }
     qpdf_offset_t start_offset = (end_offset > 1054 ? end_offset - 1054 : 0);
     PatternFinder sf(*this, &QPDF::findStartxref);
     qpdf_offset_t xref_offset = 0;
@@ -554,9 +560,6 @@ QPDF::reconstruct_xref(QPDFExc&amp; e)
  
     m->file->seek(0, SEEK_END);
     qpdf_offset_t eof = m->file->tell();
-    // Sanity check on object ids. All objects must appear in xref table / stream. In all realistic
-    // scenarios at leat 3 bytes are required.
-    auto max_obj_id = eof / 3;
     m->file->seek(0, SEEK_SET);
     qpdf_offset_t line_start = 0;
     // Don't allow very long tokens here during recovery.
@@ -574,7 +577,7 @@ QPDF::reconstruct_xref(QPDFExc&amp; e)
             if ((t2.isInteger()) && (readToken(m->file, MAX_LEN).isWord("obj"))) {
                 int obj = QUtil::string_to_int(t1.getValue().c_str());
                 int gen = QUtil::string_to_int(t2.getValue().c_str());
-                if (obj <= max_obj_id) {
+                if (obj <= m->xref_table_max_id) {
                     insertReconstructedXrefEntry(obj, token_start, gen);
                 } else {
                     warn(damagedPDF(
@@ -709,7 +712,7 @@ QPDF::read_xref(qpdf_offset_t xref_offset)
     int size = m->trailer.getKey("/Size").getIntValueAsInt();
     int max_obj = 0;
     if (!m->xref_table.empty()) {
-        max_obj = (*(m->xref_table.rbegin())).first.getObj();
+        max_obj = m->xref_table.rbegin()->first.getObj();
     }
     if (!m->deleted_objects.empty()) {
         max_obj = std::max(max_obj, *(m->deleted_objects.rbegin()));
@@ -1262,11 +1265,21 @@ QPDF::insertXrefEntry(int obj, int f0, qpdf_offset_t f1, int f2)
     // If there is already an entry for this object and generation in the table, it means that a
     // later xref table has registered this object.  Disregard this one.
  
+    if (obj > m->xref_table_max_id) {
+        // ignore impossibly large object ids or object ids > Size.
+        return;
+    }
+
     if (m->deleted_objects.count(obj)) {
         QTC::TC("qpdf", "QPDF xref deleted object");
         return;
     }
  
+    if (f0 == 2 && static_cast<int>(f1) == obj) {
+        warn(damagedPDF("xref stream", "self-referential object stream " + std::to_string(obj)));
+        return;
+    }
+
     auto [iter, created] = m->xref_table.try_emplace(QPDFObjGen(obj, (f0 == 2 ? 0 : f2)));
     if (!created) {
         QTC::TC("qpdf", "QPDF xref reused object");
@@ -1303,12 +1316,11 @@ QPDF::insertFreeXrefEntry(QPDFObjGen og)
 void
 QPDF::insertReconstructedXrefEntry(int obj, qpdf_offset_t f1, int f2)
 {
-    // Various tables are indexed by object id, with potential size id + 1
-    constexpr static int max_id = std::numeric_limits<int>::max() - 1;
-    if (!(obj > 0 && obj <= max_id && 0 <= f2 && f2 < 65535)) {
+    if (!(obj > 0 && obj <= m->xref_table_max_id && 0 <= f2 && f2 < 65535)) {
         QTC::TC("qpdf", "QPDF xref overwrite invalid objgen");
         return;
     }
+
     QPDFObjGen og(obj, f2);
     if (!m->deleted_objects.count(obj)) {
         // deleted_objects stores the uncompressed objects removed from the xref table at the start
@@ -1918,6 +1930,17 @@ QPDF::resolveObjectsInStream(int obj_stream_number)
  
         int num = QUtil::string_to_int(tnum.getValue().c_str());
         long long offset = QUtil::string_to_int(toffset.getValue().c_str());
+        if (num > m->xref_table_max_id) {
+            continue;
+        }
+        if (num == obj_stream_number) {
+            warn(damagedPDF(
+                input,
+                m->last_object_description,
+                input->getLastOffset(),
+                "object stream claims to contain itself"));
+            continue;
+        }
         offsets[num] = toI(offset + first);
     }
  
 WARNING: issue-118.pdf: can't find PDF header
-WARNING: issue-118.pdf (offset 732): loop detected resolving object 2 0
-WARNING: issue-118.pdf (xref stream: object 8 0, offset 732): supposed object stream 2 is not a stream
+WARNING: issue-118.pdf (xref stream, offset 732): self-referential object stream 2
 issue-118.pdf: unable to find /Root dictionary
+WARNING: issue-120.pdf (xref stream, offset 712): self-referential object stream 3
 qpdf: issue-120.pdf: unable to find page tree
@@ -3,6 +3,7 @@ WARNING: issue-143.pdf (xref stream: object 3 0, offset 654): stream keyword not
 WARNING: issue-143.pdf (xref stream: object 3 0, offset 607): stream dictionary lacks /Length key
 WARNING: issue-143.pdf (xref stream: object 3 0, offset 654): attempting to recover stream length
 WARNING: issue-143.pdf (xref stream: object 3 0, offset 654): recovered stream length: 36
+WARNING: issue-143.pdf (xref stream, offset 654): self-referential object stream 3
 WARNING: issue-143.pdf: file is damaged
 WARNING: issue-143.pdf (object 1 0, offset 48): expected n n obj
 WARNING: issue-143.pdf: Attempting to reconstruct cross-reference table