Fix a division by zero when processing malformed BMP files.

This fixes a division by 0 when processing a maliciously crafted BMP
file. No impact beyond DoS.

Task-number: QTBUG-44547
Change-Id: Ifcded2c0aa712e90d23e6b3969af0ec3add53973
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/gui/image/qbmphandler.cpp b/src/gui/image/qbmphandler.cpp
index 21c1a2f813..df664994d6 100644
--- a/src/gui/image/qbmphandler.cpp
+++ b/src/gui/image/qbmphandler.cpp
@@ -314,12 +314,20 @@ static bool read_dib_body(QDataStream &s, const BMP_INFOHDR &bi, int offset, int
         }
     } else if (comp == BMP_BITFIELDS && (nbits == 16 || nbits == 32)) {
         red_shift = calc_shift(red_mask);
+        if (((red_mask >> red_shift) + 1) == 0)
+            return false;
         red_scale = 256 / ((red_mask >> red_shift) + 1);
         green_shift = calc_shift(green_mask);
+        if (((green_mask >> green_shift) + 1) == 0)
+            return false;
         green_scale = 256 / ((green_mask >> green_shift) + 1);
         blue_shift = calc_shift(blue_mask);
+        if (((blue_mask >> blue_shift) + 1) == 0)
+            return false;
         blue_scale = 256 / ((blue_mask >> blue_shift) + 1);
         alpha_shift = calc_shift(alpha_mask);
+        if (((alpha_mask >> alpha_shift) + 1) == 0)
+            return false;
         alpha_scale = 256 / ((alpha_mask >> alpha_shift) + 1);
     } else if (comp == BMP_RGB && (nbits == 24 || nbits == 32)) {
         blue_mask = 0x000000ff;