[Backport] CVE-2023-0933: Integer overflow in PDF

Manual cherry-pick of patch originally reviewed on
https://pdfium-review.googlesource.com/c/pdfium/+/103078:
Validate the page count.

In CountPages(), which recursively calls itself, validate the page
count. When any part of the pages tree contains bad data, bail out.

Bug: chromium:1404864
Change-Id: Ifdbc14213ec3f963b4b2cb5793b83c15d03336e8
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/103078
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-on: https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/462769
Reviewed-by: Michal Klocek <michal.klocek@qt.io>

1 files changed, 14 insertions, 3 deletions

diff --git a/chromium/third_party/pdfium/core/fpdfapi/parser/cpdf_document.cpp b/chromium/third_party/pdfium/core/fpdfapi/parser/cpdf_document.cpp
index 44fa2a1009e..8179db37a3b 100644
--- a/chromium/third_party/pdfium/core/fpdfapi/parser/cpdf_document.cpp
+++ b/chromium/third_party/pdfium/core/fpdfapi/parser/cpdf_document.cpp
@@ -20,6 +20,7 @@
 #include "core/fxcrt/fx_codepage.h"
 #include "core/fxcrt/scoped_set_insertion.h"
 #include "core/fxcrt/stl_util.h"
+#include "third_party/abseil-cpp/absl/types/optional.h"
 #include "third_party/base/check.h"
 #include "third_party/base/containers/contains.h"
 
@@ -27,7 +28,9 @@ namespace {
 
 const int kMaxPageLevel = 1024;
 
-int CountPages(CPDF_Dictionary* pPages,
+// Returns a value in the range [0, `CPDF_Document::kPageMaxNum`), or nullopt on
+// error.
+absl::optional<int> CountPages(CPDF_Dictionary* pPages,
                std::set<CPDF_Dictionary*>* visited_pages) {
   int count = pPages->GetIntegerFor("Count");
   if (count > 0 && count < CPDF_Document::kPageMaxNum)
@@ -43,11 +46,19 @@ int CountPages(CPDF_Dictionary* pPages,
     if (pKid->KeyExist("Kids")) {
       // Use |visited_pages| to help detect circular references of pages.
       ScopedSetInsertion<CPDF_Dictionary*> local_add(visited_pages, pKid);
-      count += CountPages(pKid, visited_pages);
+      absl::optional<int> local_count =
+          CountPages(pKid, visited_pages);
+      if (!local_count.has_value()) {
+        return absl::nullopt;  // Propagate error.
+      }
+      count += local_count.value();
     } else {
       // This page is a leaf node.
       count++;
     }
+    if (count >= CPDF_Document::kPageMaxNum) {
+      return absl::nullopt;  // Error: too many pages.
+    }
   }
   pPages->SetNewFor<CPDF_Number>("Count", count);
   return count;
@@ -366,7 +377,7 @@ int CPDF_Document::RetrievePageCount() {
 
   std::set<CPDF_Dictionary*> visited_pages;
   visited_pages.insert(pPages);
-  return CountPages(pPages, &visited_pages);
+  return CountPages(pPages, &visited_pages).value_or(0);
 }
 
 uint32_t CPDF_Document::GetUserPermissions() const {