Add support for PartionRealloc to return nullptr

Currently the PartitionRealloc code path will only exit, with no
option to return nullptr on failure, unlike PartitionAlloc code path.
This CL refactors the realloc code path to be similar to alloc code
path, following the upstream patch:
https://chromium-review.googlesource.com/c/chromium/src/+/1044971

This also changes the version of realloc exposed to third party C libs
to have the nullptr behaviour, like the exposed version of alloc.

This CL is a redo of
https://pdfium-review.googlesource.com/c/pdfium/+/31990

BUG=chromium:783022

Change-Id: Ib1b659079585dfd0423d683b8a2c7b6758a22a01
Reviewed-on: https://pdfium-review.googlesource.com/32613
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>

2 files changed, 42 insertions, 15 deletions

diff --git a/third_party/base/allocator/partition_allocator/partition_alloc.cc b/third_party/base/allocator/partition_allocator/partition_alloc.cc
index ff366b861f..e8aad9420c 100644
--- a/third_party/base/allocator/partition_allocator/partition_alloc.cc
+++ b/third_party/base/allocator/partition_allocator/partition_alloc.cc
@@ -1021,22 +1021,29 @@ bool partitionReallocDirectMappedInPlace(PartitionRootGeneric* root,
   return true;
 }
 
-void* PartitionReallocGeneric(PartitionRootGeneric* root,
-                              void* ptr,
-                              size_t new_size,
-                              const char* type_name) {
+void* PartitionReallocGenericFlags(PartitionRootGeneric* root,
+                                   int flags,
+                                   void* ptr,
+                                   size_t new_size,
+                                   const char* type_name) {
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
-  return realloc(ptr, new_size);
+  void* result = realloc(ptr, new_size);
+  CHECK(result || flags & PartitionAllocReturnNull);
+  return result;
 #else
   if (UNLIKELY(!ptr))
-    return PartitionAllocGeneric(root, new_size, type_name);
+    return PartitionAllocGenericFlags(root, flags, new_size, type_name);
   if (UNLIKELY(!new_size)) {
     PartitionFreeGeneric(root, ptr);
-    return 0;
+    return nullptr;
   }
 
-  if (new_size > kGenericMaxDirectMapped)
-    PartitionExcessiveAllocationSize();
+  if (new_size > kGenericMaxDirectMapped) {
+    if (flags & PartitionAllocReturnNull)
+      return nullptr;
+    else
+      PartitionExcessiveAllocationSize();
+  }
 
   DCHECK(PartitionPointerIsValid(PartitionCookieFreePointerAdjust(ptr)));
 
@@ -1069,12 +1076,19 @@ void* PartitionReallocGeneric(PartitionRootGeneric* root,
     // |new_size| via the raw size pointer.
     if (PartitionPageGetRawSizePtr(page))
       PartitionCookieWriteValue(static_cast<char*>(ptr) + new_size);
-#endif
+#endif  // DCHECK_IS_ON()
     return ptr;
   }
 
   // This realloc cannot be resized in-place. Sadness.
-  void* ret = PartitionAllocGeneric(root, new_size, type_name);
+  void* ret = PartitionAllocGenericFlags(root, flags, new_size, type_name);
+  if (!ret) {
+    if (flags & PartitionAllocReturnNull)
+      return nullptr;
+    else
+      PartitionExcessiveAllocationSize();
+  }
+
   size_t copy_size = actual_old_size;
   if (new_size < copy_size)
     copy_size = new_size;
@@ -1082,7 +1096,14 @@ void* PartitionReallocGeneric(PartitionRootGeneric* root,
   memcpy(ret, ptr, copy_size);
   PartitionFreeGeneric(root, ptr);
   return ret;
-#endif
+#endif  // defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
+}
+
+void* PartitionReallocGeneric(PartitionRootGeneric* root,
+                              void* ptr,
+                              size_t new_size,
+                              const char* type_name) {
+  return PartitionReallocGenericFlags(root, 0, ptr, new_size, type_name);
 }
 
 static size_t PartitionPurgePage(PartitionPage* page, bool discard) {
diff --git a/third_party/base/allocator/partition_allocator/partition_alloc.h b/third_party/base/allocator/partition_allocator/partition_alloc.h
index 87db329af2..69fba97d62 100644
--- a/third_party/base/allocator/partition_allocator/partition_alloc.h
+++ b/third_party/base/allocator/partition_allocator/partition_alloc.h
@@ -432,9 +432,15 @@ BASE_EXPORT NOINLINE void* PartitionAllocSlowPath(PartitionRootBase*,
                                                   size_t,
                                                   PartitionBucket*);
 BASE_EXPORT NOINLINE void PartitionFreeSlowPath(PartitionPage*);
-BASE_EXPORT NOINLINE void* PartitionReallocGeneric(PartitionRootGeneric*,
-                                                   void*,
-                                                   size_t,
+BASE_EXPORT NOINLINE void* PartitionReallocGenericFlags(
+    PartitionRootGeneric* root,
+    int flags,
+    void* ptr,
+    size_t new_size,
+    const char* type_name);
+BASE_EXPORT NOINLINE void* PartitionReallocGeneric(PartitionRootGeneric* root,
+                                                   void* ptr,
+                                                   size_t new_size,
                                                    const char* type_name);
 
 BASE_EXPORT void PartitionDumpStats(PartitionRoot*,