Make is_ktx safer

third_party/ktx/ktx.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "ktx.h"
 #include "SkBitmap.h"
 #include "SkStream.h"
@@ skipping 318 matching lines @@
         }
 
         uint32_t imgSizePadded = (imgSize + 3) & ~3;
         buf += imgSizePadded;
         bytesLeft -= imgSizePadded;
     }
 
     return bytesLeft == 0;
 }
 
-bool SkKTXFile::is_ktx(const uint8_t *data) {
-    return 0 == memcmp(KTX_FILE_IDENTIFIER, data, KTX_FILE_IDENTIFIER_SIZE);
+bool SkKTXFile::is_ktx(const uint8_t data[], size_t size) {
+    return size >= KTX_FILE_IDENTIFIER_SIZE &&
+           0 == memcmp(KTX_FILE_IDENTIFIER, data, KTX_FILE_IDENTIFIER_SIZE);
 }
 
 bool SkKTXFile::is_ktx(SkStreamRewindable* stream) {
     // Read the KTX header and make sure it's valid.
     unsigned char buf[KTX_FILE_IDENTIFIER_SIZE];
     bool largeEnough =
         stream->read((void*)buf, KTX_FILE_IDENTIFIER_SIZE) == KTX_FILE_IDENTIFIER_SIZE;
     stream->rewind();
     if (!largeEnough) {
         return false;
     }
-    return is_ktx(buf);
+    return is_ktx(buf, KTX_FILE_IDENTIFIER_SIZE);
 }
 
 SkKTXFile::KeyValue SkKTXFile::CreateKeyValue(const char *cstrKey, const char *cstrValue) {
     SkString key(cstrKey);
     SkString value(cstrValue);
 
     // Size of buffer is length of string plus the null terminators...
     size_t size = key.size() + 1 + value.size() + 1;
 
     SkAutoSMalloc<256> buf(size);
@@ skipping 186 matching lines @@
         for (int i = 0; i < height; ++i) {
             if (!stream->write(rowPtr, bpp*width)) {
                 return false;
             }
             rowPtr += bitmap.rowBytes();
         }
     }
 
     return true;
 }