Fixed crash in image reader when reading certain BMP files.

If the high bit in a mask is set, for instance if the mask is
0xff000000, and we shift it to the right by 24 positions, since the mask
was not declared as unsigned we ended up with a mask value of
0xffffffff. We then add 1 to this value and divide by the result,
causing a division by zero crash.

The masks need to be declared unsigned to prevent sign bit extension
when shifting right.

Task-number: QTBUG-29194
Change-Id: I1003d546a70d540b5c135b6b75dee9b4962a7210
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
(cherry picked from qtbase, af84313c622af880e95d461ea8b7dbca58d2dffa)

1 files changed, 4 insertions, 4 deletions

diff --git a/src/gui/image/qbmphandler.cpp b/src/gui/image/qbmphandler.cpp
index d59c9d73e0..3d02caa3d9 100644
--- a/src/gui/image/qbmphandler.cpp
+++ b/src/gui/image/qbmphandler.cpp
@@ -143,7 +143,7 @@ static QDataStream &operator<<(QDataStream &s, const BMP_INFOHDR &bi)
     return s;
 }
 
-static int calc_shift(int mask)
+static int calc_shift(uint mask)
 {
     int result = 0;
     while (mask && !(mask & 1)) {
@@ -207,9 +207,9 @@ static bool read_dib_body(QDataStream &s, const BMP_INFOHDR &bi, int offset, int
 #endif
     int w = bi.biWidth,         h = bi.biHeight,  nbits = bi.biBitCount;
     int t = bi.biSize,         comp = bi.biCompression;
-    int red_mask = 0;
-    int green_mask = 0;
-    int blue_mask = 0;
+    uint red_mask = 0;
+    uint green_mask = 0;
+    uint blue_mask = 0;
     int red_shift = 0;
     int green_shift = 0;
     int blue_shift = 0;