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

include/core/SkReader32.h

Index: include/core/SkReader32.h
diff --git a/include/core/SkReader32.h b/include/core/SkReader32.h
index 7a8d22a80c166c82539f05fe9d83186269416762..71101c333474bb70ad642052d0f3025fa23df924 100644
--- a/include/core/SkReader32.h
+++ b/include/core/SkReader32.h
@@ -107,13 +107,13 @@ public:
     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);
     }
@@ -124,7 +124,7 @@ public:
     }
 
     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);
     }