Fix buffer overflow in text blending

Clip buffers being converted to those being worked on so we don't write
outside the lines.

Task-number: QTBUG-61863
Change-Id: Icc7c6c0946fa522b5afeca0663fc2b45151b1897
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

1 files changed, 4 insertions, 4 deletions

diff --git a/src/gui/painting/qdrawhelper.cpp b/src/gui/painting/qdrawhelper.cpp
index 82aceb93c7..aca31cf3e8 100644
--- a/src/gui/painting/qdrawhelper.cpp
+++ b/src/gui/painting/qdrawhelper.cpp
@@ -5625,13 +5625,13 @@ static void qt_alphamapblit_generic(QRasterBuffer *rasterBuffer,
                 int start = qMax<int>(x, clip.x);
                 int end = qMin<int>(x + mapWidth, clip.x + clip.len);
                 Q_ASSERT(clip.len <= buffer_size);
-                QRgba64 *dest = destFetch64((QRgba64*)buffer, rasterBuffer, start, clip.y, clip.len);
+                QRgba64 *dest = destFetch64((QRgba64*)buffer, rasterBuffer, start, clip.y, end - start);
 
                 for (int xp=start; xp<end; ++xp) {
                     const int coverage = map[xp - x];
                     alphamapblend_generic(coverage, dest, xp - start, srcColor, color, colorProfile);
                 }
-                destStore64(rasterBuffer, start, clip.y, dest, clip.len);
+                destStore64(rasterBuffer, start, clip.y, dest, end - start);
             } // for (i -> line.count)
             map += mapStride;
         } // for (yp -> bottom)
@@ -5898,13 +5898,13 @@ static void qt_alphargbblit_generic(QRasterBuffer *rasterBuffer,
                 int start = qMax<int>(x, clip.x);
                 int end = qMin<int>(x + mapWidth, clip.x + clip.len);
                 Q_ASSERT(clip.len <= buffer_size);
-                QRgba64 *dest = destFetch64((QRgba64*)buffer, rasterBuffer, start, clip.y, clip.len);
+                QRgba64 *dest = destFetch64((QRgba64*)buffer, rasterBuffer, start, clip.y, end - start);
 
                 for (int xp=start; xp<end; ++xp) {
                     const uint coverage = src[xp - x];
                     alphargbblend_generic(coverage, dest, xp - start, srcColor, color, colorProfile);
                 }
-                destStore64(rasterBuffer, start, clip.y, dest, clip.len);
+                destStore64(rasterBuffer, start, clip.y, dest, end - start);
             } // for (i -> line.count)
             src += srcStride;
         } // for (yp -> bottom)