Fix overflow caught by ASAN.

src/codec/SkBmpStandardCodec.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBmpStandardCodec.h"
 #include "SkCodecPriv.h"
 #include "SkColorPriv.h"
 #include "SkStream.h"
 
 /*
  * Creates an instance of the decoder
  * Called only by NewFromStream
  */
 SkBmpStandardCodec::SkBmpStandardCodec(const SkImageInfo& info, SkStream* stream,
                                        uint16_t bitsPerPixel, uint32_t numColors,
                                        uint32_t bytesPerColor, uint32_t offset,
                                        SkCodec::SkScanlineOrder rowOrder, bool inIco)
     : INHERITED(info, stream, bitsPerPixel, rowOrder)
     , fColorTable(nullptr)
-    , fNumColors(this->computeNumColors(numColors))
+    , fNumColors(numColors)
     , fBytesPerColor(bytesPerColor)
     , fOffset(offset)
     , fSwizzler(nullptr)
     , fSrcRowBytes(SkAlign4(compute_row_bytes(this->getInfo().width(), this->bitsPerPixel())))
     , fSrcBuffer(new uint8_t [fSrcRowBytes])
     , fInIco(inIco)
 {}
 
 /*
  * Initiates the bitmap decode
@@ skipping 41 matching lines @@
     SkPMColor colorTable[256];
     if (this->bitsPerPixel() <= 8) {
         // Inform the caller of the number of colors
         uint32_t maxColors = 1 << this->bitsPerPixel();
         if (nullptr != numColors) {
             // We set the number of colors to maxColors in order to ensure
             // safe memory accesses.  Otherwise, an invalid pixel could
             // access memory outside of our color table array.
             *numColors = maxColors;
         }
+        // Don't bother reading more than maxColors.
+        const uint32_t numColorsToRead =
+            fNumColors == 0 ? maxColors : SkTMin(fNumColors, maxColors);
 
         // Read the color table from the stream
-        colorBytes = fNumColors * fBytesPerColor;
+        colorBytes = numColorsToRead * fBytesPerColor;
         SkAutoTDeleteArray<uint8_t> cBuffer(new uint8_t[colorBytes]);
         if (stream()->read(cBuffer.get(), colorBytes) != colorBytes) {
             SkCodecPrintf("Error: unable to read color table.\n");
             return false;
         }
 
         // Choose the proper packing function
         SkPMColor (*packARGB) (uint32_t, uint32_t, uint32_t, uint32_t);
         switch (alphaType) {
             case kOpaque_SkAlphaType:
             case kUnpremul_SkAlphaType:
                 packARGB = &SkPackARGB32NoCheck;
                 break;
             case kPremul_SkAlphaType:
                 packARGB = &SkPreMultiplyARGB;
                 break;
             default:
                 // This should not be reached because conversion possible
                 // should fail if the alpha type is not one of the above
                 // values.
                 SkASSERT(false);
                 packARGB = nullptr;
                 break;
         }
 
         // Fill in the color table
         uint32_t i = 0;
-        for (; i < fNumColors; i++) {
+        for (; i < numColorsToRead; i++) {
             uint8_t blue = get_byte(cBuffer.get(), i*fBytesPerColor);
             uint8_t green = get_byte(cBuffer.get(), i*fBytesPerColor + 1);
             uint8_t red = get_byte(cBuffer.get(), i*fBytesPerColor + 2);
             uint8_t alpha;
             if (kOpaque_SkAlphaType == alphaType) {
                 alpha = 0xFF;
             } else {
                 alpha = get_byte(cBuffer.get(), i*fBytesPerColor + 3);
             }
             colorTable[i] = packARGB(alpha, red, green, blue);
@@ skipping 163 matching lines @@
     return kSuccess;
 }
 
 uint32_t SkBmpStandardCodec::onGetFillValue(SkColorType colorType, SkAlphaType alphaType) const {
     const SkPMColor* colorPtr = get_color_ptr(fColorTable.get());
     if (colorPtr) {
         return get_color_table_fill_value(colorType, colorPtr, 0);
     }
     return INHERITED::onGetFillValue(colorType, alphaType);
 }