Tighten up masking of colorType & alphaType in SkImageInfo serialization (for fuzzer bug)

src/core/SkImageInfo.cpp

 /*
  * Copyright 2010 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageInfo.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 
 static bool alpha_type_is_valid(SkAlphaType alphaType) {
     return (alphaType >= 0) && (alphaType <= kLastEnum_SkAlphaType);
 }
 
 static bool color_type_is_valid(SkColorType colorType) {
     return (colorType >= 0) && (colorType <= kLastEnum_SkColorType);
 }
 
 SkImageInfo SkImageInfo::MakeS32(int width, int height, SkAlphaType at) {
     return SkImageInfo(width, height, kN32_SkColorType, at,
                        SkColorSpace::NewNamed(SkColorSpace::kSRGB_Named));
 }
 
+static const int kColorTypeMask = 0x0F;
+static const int kAlphaTypeMask = 0x03;
+
 void SkImageInfo::unflatten(SkReadBuffer& buffer) {
     fWidth = buffer.read32();
     fHeight = buffer.read32();
 
     uint32_t packed = buffer.read32();
-    SkASSERT(0 == (packed >> 24));
-    fColorType = (SkColorType)((packed >> 0) & 0xFF);
-    fAlphaType = (SkAlphaType)((packed >> 8) & 0xFF);
+    fColorType = (SkColorType)((packed >> 0) & kColorTypeMask);
+    fAlphaType = (SkAlphaType)((packed >> 8) & kAlphaTypeMask);
     buffer.validate(alpha_type_is_valid(fAlphaType) && color_type_is_valid(fColorType));
 
     sk_sp<SkData> data = buffer.readByteArrayAsData();
     fColorSpace = SkColorSpace::Deserialize(data->data(), data->size());
 }
 
 void SkImageInfo::flatten(SkWriteBuffer& buffer) const {
     buffer.write32(fWidth);
     buffer.write32(fHeight);
 
-    SkASSERT(0 == (fAlphaType & ~0xFF));
-    SkASSERT(0 == (fColorType & ~0xFF));
+    SkASSERT(0 == (fAlphaType & ~kAlphaTypeMask));
+    SkASSERT(0 == (fColorType & ~kColorTypeMask));
     uint32_t packed = (fAlphaType << 8) | fColorType;
     buffer.write32(packed);
 
     if (fColorSpace) {
         sk_sp<SkData> data = fColorSpace->serialize();
         if (data) {
             buffer.writeDataAsByteArray(data.get());
         } else {
             buffer.writeByteArray(nullptr, 0);
         }
@@ skipping 71 matching lines @@
     }
     // here x,y are either 0 or negative
     fPixels = ((char*)fPixels - y * fRowBytes - x * fInfo.bytesPerPixel());
     // the intersect may have shrunk info's logical size
     fInfo = fInfo.makeWH(srcR.width(), srcR.height());
     fX = srcR.x();
     fY = srcR.y();
 
     return true;
 }