Clean up SkPathRef::makeSpace.

Note that this does not clean up the users of this function, which
may themselves be subject to other overflow issues.

BUG=chromium:728936

Change-Id: I3eaa7627c3b6ff49296ea2618a0157dacdc1d9cc
Reviewed-on: https://skia-review.googlesource.com/29121
Commit-Queue: Ben Wagner <bungeman@google.com>
Reviewed-by: Mike Klein <mtklein@chromium.org>
Reviewed-by: Ben Wagner <bungeman@google.com>

1 files changed, 14 insertions, 10 deletions

diff --git a/include/private/SkPathRef.h b/include/private/SkPathRef.h
index 5e6fda7d85..0efea72a86 100644
--- a/include/private/SkPathRef.h
+++ b/include/private/SkPathRef.h
@@ -16,7 +16,7 @@
 #include "SkRRect.h"
 #include "SkRect.h"
 #include "SkRefCnt.h"
-#include <stddef.h> // ptrdiff_t
+#include "SkTemplates.h"
 
 class SkRBuffer;
 class SkWBuffer;
@@ -433,31 +433,35 @@ private:
      */
     void makeSpace(size_t size) {
         SkDEBUGCODE(this->validate();)
-        ptrdiff_t growSize = size - fFreeSpace;
-        if (growSize <= 0) {
+        if (size <= fFreeSpace) {
             return;
         }
+        size_t growSize = size - fFreeSpace;
         size_t oldSize = this->currSize();
         // round to next multiple of 8 bytes
         growSize = (growSize + 7) & ~static_cast<size_t>(7);
         // we always at least double the allocation
-        if (static_cast<size_t>(growSize) < oldSize) {
+        if (growSize < oldSize) {
             growSize = oldSize;
         }
         if (growSize < kMinSize) {
             growSize = kMinSize;
         }
-        size_t newSize = oldSize + growSize;
+        constexpr size_t maxSize = std::numeric_limits<size_t>::max();
+        size_t newSize;
+        if (growSize <= maxSize - oldSize) {
+            newSize = oldSize + growSize;
+        } else {
+            SK_ABORT("Path too big.");
+        }
         // Note that realloc could memcpy more than we need. It seems to be a win anyway. TODO:
         // encapsulate this.
         fPoints = reinterpret_cast<SkPoint*>(sk_realloc_throw(fPoints, newSize));
         size_t oldVerbSize = fVerbCnt * sizeof(uint8_t);
-        void* newVerbsDst = reinterpret_cast<void*>(
-                                reinterpret_cast<intptr_t>(fPoints) + newSize - oldVerbSize);
-        void* oldVerbsSrc = reinterpret_cast<void*>(
-                                reinterpret_cast<intptr_t>(fPoints) + oldSize - oldVerbSize);
+        void* newVerbsDst = SkTAddOffset<void>(fPoints, newSize - oldVerbSize);
+        void* oldVerbsSrc = SkTAddOffset<void>(fPoints, oldSize - oldVerbSize);
         memmove(newVerbsDst, oldVerbsSrc, oldVerbSize);
-        fVerbs = reinterpret_cast<uint8_t*>(reinterpret_cast<intptr_t>(fPoints) + newSize);
+        fVerbs = SkTAddOffset<uint8_t>(fPoints, newSize);
         fFreeSpace += growSize;
         SkDEBUGCODE(this->validate();)
     }