Convert strides with padding in skia::SkBitmapToN32OpaqueOrPremul().

Code using bitmaps converted with SkBitmapToN32OpaqueOrPremul() can
easily assume that the pixels are one contiguous (width*4*height)-sized
buffer. If it's not then out-of-bounds read/write can occur.

Also adds tests for SkBitmapToN32OpaqueOrPremul().

R=fmalita@chromium.org

Bug: 1147431, 1144462
Change-Id: I21f7a958a8c9231bf5f052f8ff246f2c249bd70b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2544032
Commit-Queue: danakj <danakj@chromium.org>
Reviewed-by: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#828406}

skia/BUILD.gn

@@ -918,6 +918,7 @@ test("skia_unittests") {
     "ext/platform_canvas_unittest.cc",
     "ext/recursive_gaussian_convolution_unittest.cc",
     "ext/skia_memory_dump_provider_unittest.cc",
+    "ext/skia_utils_base_unittest.cc",
   ]
   if (is_ios) {
     sources += [ "ext/skia_utils_ios_unittest.mm" ]

skia/ext/skia_utils_base.cc

@@ -92,7 +92,8 @@ bool SkBitmapToN32OpaqueOrPremul(const SkBitmap& in, SkBitmap* out) {
     return true;
   }
   const SkImageInfo& info = in.info();
-  if (info.colorType() == kN32_SkColorType &&
+  const bool stride_matches_width = in.rowBytes() == info.minRowBytes();
+  if (stride_matches_width && info.colorType() == kN32_SkColorType &&
       (info.alphaType() == kPremul_SkAlphaType ||
        info.alphaType() == kOpaque_SkAlphaType)) {
     // Shallow copy if the data is already in the right format.

skia/ext/skia_utils_base.h

@@ -42,9 +42,10 @@ SK_API void WriteSkFontIdentity(
 // Writes style into the request pickle.
 SK_API void WriteSkFontStyle(base::Pickle* pickle, SkFontStyle style);
 
-// Converts an SkBitmap to an Opaque or Premul N32 SkBitmap. If the input is in
-// the right format (N32 Opaque or Premul) already, points |out| directly at
-// |in|. |out| may or may not be GPU-backed.
+// Converts an SkBitmap to an Opaque or Premul N32 SkBitmap with stride matching
+// the width of each row. If the input is has the right format (N32 Opaque or
+// Premul) without stride padding already, this assigns `in` to `out`, sharing
+// the backing pixels. `out` may or may not be GPU-backed.
 //
 // If unsuccessful, returns false, but |out| may be modified.
 //

skia/ext/skia_utils_base_unittest.cc

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "skia/ext/skia_utils_base.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/skia/include/core/SkBitmap.h"
+#include "third_party/skia/include/core/SkImageInfo.h"
+
+namespace skia {
+namespace {
+
+#define EXPECT_EQ_BITMAP(a, b)                               \
+  do {                                                       \
+    EXPECT_EQ(a.pixmap().addr(), b.pixmap().addr());         \
+    EXPECT_EQ(a.pixmap().rowBytes(), b.pixmap().rowBytes()); \
+    EXPECT_EQ(a.pixmap().info(), b.pixmap().info());         \
+  } while (false)
+
+TEST(SkiaUtilsBase, ConvertNullToN32) {
+  SkBitmap bitmap;
+  SkBitmap out;
+  EXPECT_TRUE(SkBitmapToN32OpaqueOrPremul(bitmap, &out));
+  // Returned a copy of the input bitmap.
+  EXPECT_EQ_BITMAP(bitmap, out);
+}
+
+TEST(SkiaUtilsBase, ConvertValidToN32) {
+  SkBitmap bitmap;
+  bitmap.allocN32Pixels(10, 12);
+  SkBitmap out;
+  EXPECT_TRUE(SkBitmapToN32OpaqueOrPremul(bitmap, &out));
+  // Returned a copy of the input bitmap.
+  EXPECT_EQ_BITMAP(bitmap, out);
+}
+
+TEST(SkiaUtilsBase, ConvertWeirdStrideToN32) {
+  int width = 10;
+  int height = 12;
+
+  SkBitmap bitmap;
+  // Stride is > 4 * width.
+  bitmap.allocPixels(SkImageInfo::MakeN32(width, height, kPremul_SkAlphaType),
+                     width * 4 + 4);
+
+  SkBitmap out;
+  EXPECT_TRUE(SkBitmapToN32OpaqueOrPremul(bitmap, &out));
+  // The stride was converted.
+  EXPECT_NE(bitmap.rowBytes(), out.rowBytes());
+  EXPECT_EQ(out.rowBytes(), width * 4u);
+}
+
+TEST(SkiaUtilsBase, ConvertWeirdFormatToN32) {
+  int width = 10;
+  int height = 12;
+
+  // A format smaller than N32.
+  {
+    SkBitmap bitmap;
+    bitmap.allocPixels(SkImageInfo::MakeA8(width, height));
+
+    SkBitmap out;
+    EXPECT_TRUE(SkBitmapToN32OpaqueOrPremul(bitmap, &out));
+    // The format was converted.
+    EXPECT_NE(bitmap.rowBytes(), out.rowBytes());
+    EXPECT_NE(bitmap.info().colorType(), out.info().colorType());
+    EXPECT_EQ(out.rowBytes(), width * 4u);
+    EXPECT_EQ(out.info().colorType(), kN32_SkColorType);
+  }
+
+  // A format larger than N32.
+  {
+    SkBitmap bitmap;
+    bitmap.allocPixels(SkImageInfo::Make(width, height, kRGBA_F16_SkColorType,
+                                         kPremul_SkAlphaType));
+
+    SkBitmap out;
+    EXPECT_TRUE(SkBitmapToN32OpaqueOrPremul(bitmap, &out));
+    // The format was converted.
+    EXPECT_NE(bitmap.rowBytes(), out.rowBytes());
+    EXPECT_NE(bitmap.info().colorType(), out.info().colorType());
+    EXPECT_EQ(out.rowBytes(), width * 4u);
+    EXPECT_EQ(out.info().colorType(), kN32_SkColorType);
+  }
+}
+
+}  // namespace
+}  // namespace skia