Add safe FX_Alloc2D() macro

This avoids unchecked multiplications when computing a size argument
to malloc(). Such an overflow is very scary, and can result in
exploitable bugs.

Along the way, kill off some return checks, since we know this can't
return NULL.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1143663004

4 files changed, 7 insertions, 15 deletions

diff --git a/core/src/fxge/agg/agg23/fx_agg_path_storage.cpp b/core/src/fxge/agg/agg23/fx_agg_path_storage.cpp
index 8c4b701ebe..b4b184e0a4 100644
--- a/core/src/fxge/agg/agg23/fx_agg_path_storage.cpp
+++ b/core/src/fxge/agg/agg23/fx_agg_path_storage.cpp
@@ -51,10 +51,7 @@ void path_storage::allocate_block(unsigned nb)
 {
     if(nb >= m_max_blocks) {
         FX_FLOAT** new_coords =
-            FX_Alloc( FX_FLOAT*, (m_max_blocks + block_pool) * 2);
-        if (!new_coords) {
-            return;
-        }
+            FX_Alloc2D(FX_FLOAT*, m_max_blocks + block_pool, 2);
         unsigned char** new_cmds =
             (unsigned char**)(new_coords + m_max_blocks + block_pool);
         if(m_coord_blocks) {
diff --git a/core/src/fxge/dib/fx_dib_engine.cpp b/core/src/fxge/dib/fx_dib_engine.cpp
index 5053c306f5..7c40171c2b 100644
--- a/core/src/fxge/dib/fx_dib_engine.cpp
+++ b/core/src/fxge/dib/fx_dib_engine.cpp
@@ -316,10 +316,7 @@ FX_BOOL CStretchEngine::StartStretchHorz()
         return FALSE;
     }
     if (m_pSource && m_bHasAlpha && m_pSource->m_pAlphaMask) {
-        m_pExtraAlphaBuf = FX_Alloc(unsigned char, m_SrcClip.Height() * m_ExtraMaskPitch);
-        if (!m_pExtraAlphaBuf) {
-            return FALSE;
-        }
+        m_pExtraAlphaBuf = FX_Alloc2D(unsigned char, m_SrcClip.Height(), m_ExtraMaskPitch);
         FX_DWORD size = (m_DestClip.Width() * 8 + 31) / 32 * 4;
         m_pDestMaskScanline = FX_TryAlloc(unsigned char, size);
         if (!m_pDestMaskScanline) {
diff --git a/core/src/fxge/skia/fx_skia_device.cpp b/core/src/fxge/skia/fx_skia_device.cpp
index cc4059dd1d..a483eca5ca 100644
--- a/core/src/fxge/skia/fx_skia_device.cpp
+++ b/core/src/fxge/skia/fx_skia_device.cpp
@@ -210,7 +210,7 @@ static void SkRasterizeStroke(SkPaint& spaint, SkPath* dstPathData, SkPath& path
 		dstPathData->transform(smatrix);
 	} else {
 		int count = (pGraphState->m_DashCount+1)/2;
-		SkScalar* intervals = FX_Alloc(SkScalar, count* sizeof (SkScalar));
+		SkScalar* intervals = FX_Alloc2D(SkScalar, count, sizeof(SkScalar));
 		// Set dash pattern
 		for (int i = 0; i < count; i ++) {
 			FX_FIXFLOAT on = pGraphState->m_DashArray[i*2];
diff --git a/core/src/fxge/win32/fx_win32_gdipext.cpp b/core/src/fxge/win32/fx_win32_gdipext.cpp
index fae1883f4d..49c3f2b0cf 100644
--- a/core/src/fxge/win32/fx_win32_gdipext.cpp
+++ b/core/src/fxge/win32/fx_win32_gdipext.cpp
@@ -1266,16 +1266,14 @@ CFX_DIBitmap* CGdiplusExt::LoadDIBitmap(WINDIB_Open_Args_ args)
     int height = abs(pInfo->pbmi->bmiHeader.biHeight);
     int width = pInfo->pbmi->bmiHeader.biWidth;
     int dest_pitch = (width * pInfo->pbmi->bmiHeader.biBitCount + 31) / 32 * 4;
-    LPBYTE pData = FX_Alloc(BYTE, dest_pitch * height);
-    if (pData == NULL) {
-        FreeDIBitmap(pInfo);
-        return NULL;
-    }
+    LPBYTE pData = FX_Alloc2D(BYTE, dest_pitch, height);
     if (dest_pitch == pInfo->Stride) {
         FXSYS_memcpy32(pData, pInfo->pScan0, dest_pitch * height);
-    } else for (int i = 0; i < height; i ++) {
+    } else {
+        for (int i = 0; i < height; i ++) {
             FXSYS_memcpy32(pData + dest_pitch * i, pInfo->pScan0 + pInfo->Stride * i, dest_pitch);
         }
+    }
     CFX_DIBitmap* pDIBitmap = _FX_WindowsDIB_LoadFromBuf(pInfo->pbmi, pData, pInfo->pbmi->bmiHeader.biBitCount == 32);
     FX_Free(pData);
     FreeDIBitmap(pInfo);