Checking structure sizes before reading them from memory to avoid overflowing the buffer's stream.

include/core/SkReader32.h

 
 /*
  * Copyright 2008 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkReader32_DEFINED
@@ skipping 89 matching lines @@
         fCurr += SkAlign4(size);
         SkASSERT(fCurr <= fStop);
     }
 
     uint8_t readU8() { return (uint8_t)this->readInt(); }
     uint16_t readU16() { return (uint16_t)this->readInt(); }
     int32_t readS32() { return this->readInt(); }
     uint32_t readU32() { return this->readInt(); }
 
     void readPath(SkPath* path) {
-        size_t size = path->readFromMemory(this->peek());
+        size_t size = path->readFromMemory(this->peek(), this->available());
         SkASSERT(SkAlign4(size) == size);
         (void)this->skip(size);

[reed1, 2013/10/29 19:42:58]

if readFromMemory returns 0 (e.g. truncated stream), shouldn't we skip available
instead of zero?

[sugoi1, 2013/10/29 20:16:47]

Ok (I had to think about it a little). This would automatically cause an error
on the next read operation, either by asserting in debug or by reading
out-of-bounds in release (which is a bit more unpredictable), but it's probably
better overall than leaving peek() at its current position, since that would
increase the chance of trapping an error.

[Stephen White, 2013/10/29 20:40:54]

Reading out-of-bounds doesn't sound good. Is that something that only the
non-validating code will trigger?

BTW, is there a way we can make unit tests for all these cases? Perhaps by
serializing a valid stream, truncating it at specific points and attempting to
deserialize that?

     }
 
     void readMatrix(SkMatrix* matrix) {
-        size_t size = matrix->readFromMemory(this->peek());
+        size_t size = matrix->readFromMemory(this->peek(), this->available());
         SkASSERT(SkAlign4(size) == size);
         (void)this->skip(size);
     }
 
     SkRRect* readRRect(SkRRect* rrect) {
         rrect->readFromMemory(this->skip(SkRRect::kSizeInMemory));
         return rrect;
     }
 
     void readRegion(SkRegion* rgn) {
-        size_t size = rgn->readFromMemory(this->peek());
+        size_t size = rgn->readFromMemory(this->peek(), this->available());
         SkASSERT(SkAlign4(size) == size);
         (void)this->skip(size);
     }
 
     /**
      *  Read the length of a string (written by SkWriter32::writeString) into
      *  len (if len is not NULL) and return the null-ternimated address of the
      *  string within the reader's buffer.
      */
     const char* readString(size_t* len = NULL);
@@ skipping 11 matching lines @@
     const char* fBase;  // beginning of buffer
 
 #ifdef SK_DEBUG
     static bool ptr_align_4(const void* ptr) {
         return (((const char*)ptr - (const char*)NULL) & 3) == 0;
     }
 #endif
 };
 
 #endif