[Backport] Fix for CVE-2018-17478

Merged: [array] Ensure PrepareElementsForSort returns a legal value

PrepareElementsForSort must return a number less than or equal the array
length.

No-Try: true
No-Presubmit: true
No-Treechecks: true
Bug: chromium:897512, v8:7382
Change-Id: If5f9c4d052e623ab9f3300b8534603abbee859fa
Reviewed-on: https://chromium-review.googlesource.com/c/1297958
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#56982}
Reviewed-on: https://chromium-review.googlesource.com/c/1304354
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/branch-heads/7.0@{#67}
Cr-Branched-From: 6e2adae6f7f8e891cfd01f3280482b20590427a6-refs/heads/7.0.276@{#1}
Cr-Branched-From: bc08a8624cbbea7a2d30071472bc73ad9544eadf-refs/heads/master@{#55424}
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

2 files changed, 12 insertions, 1 deletions

diff --git a/chromium/v8/src/js/array.js b/chromium/v8/src/js/array.js
index 35db963d183..f5617919a86 100644
--- a/chromium/v8/src/js/array.js
+++ b/chromium/v8/src/js/array.js
@@ -793,6 +793,7 @@ function InnerArraySort(array, length, comparefn) {
   // array and move the undefineds after that. Holes are removed.
   // This happens for Array as well as non-Array objects.
   var num_non_undefined = %PrepareElementsForSort(array, length);
+  assert(num_non_undefined <= length);
 
   QuickSort(array, 0, num_non_undefined);
 
diff --git a/chromium/v8/src/runtime/runtime-array.cc b/chromium/v8/src/runtime/runtime-array.cc
index ae23c99910b..9f2442812fb 100644
--- a/chromium/v8/src/runtime/runtime-array.cc
+++ b/chromium/v8/src/runtime/runtime-array.cc
@@ -151,7 +151,15 @@ Object* RemoveArrayHolesGeneric(Isolate* isolate, Handle<JSReceiver> receiver,
     MAYBE_RETURN(delete_result, ReadOnlyRoots(isolate).exception());
   }
 
-  return *isolate->factory()->NewNumberFromUint(result);
+  // TODO(jgruber, szuend, chromium:897512): This is a workaround to prevent
+  // returning a number greater than array.length to Array.p.sort, which could
+  // trigger OOB accesses. There is still a correctness bug here though in
+  // how we shift around undefineds and delete elements in the two blocks above.
+  // This needs to be fixed soon.
+  const uint32_t number_of_non_undefined_elements = std::min(limit, result);
+
+  return *isolate->factory()->NewNumberFromUint(
+      number_of_non_undefined_elements);
 }
 
 // Collects all defined (non-hole) and non-undefined (array) elements at the
@@ -168,6 +176,7 @@ Object* RemoveArrayHoles(Isolate* isolate, Handle<JSReceiver> receiver,
   Handle<JSObject> object = Handle<JSObject>::cast(receiver);
   if (object->HasStringWrapperElements()) {
     int len = String::cast(Handle<JSValue>::cast(object)->value())->length();
+    DCHECK_LE(len, limit);
     return Smi::FromInt(len);
   }
 
@@ -290,6 +299,7 @@ Object* RemoveArrayHoles(Isolate* isolate, Handle<JSReceiver> receiver,
     }
   }
 
+  DCHECK_LE(result, limit);
   return *isolate->factory()->NewNumberFromUint(result);
 }