Add some sanity and bounds checking

Since QImage does sanity checking for overflows and stuff wrt.
dimensions and depth, check for QImage::isNull() as early as possible to
see if there's some funky business going on.

Also tried to add some checks wherever we wrote to "raw" memory.

Unit tests pass, and tested converting some files from
https://samples.ffmpeg.org/image-samples/ to pngs, and that seemed to
work.

Reviewed By: aacid

Differential Revision: https://phabricator.kde.org/D24367

src/imageformats/psd.cpp

@@ -171,10 +171,20 @@ static bool LoadPSD(QDataStream &stream, const PSDHeader &header, QImage &img)
         channel_num = 4;
     }
     img = QImage(header.width, header.height, fmt);
+    if (img.isNull()) {
+        qWarning() << "Failed to allocate image, invalid dimensions?" << QSize(header.width, header.height);
+        return false;
+    }
     img.fill(qRgb(0,0,0));
 
     const quint32 pixel_count = header.height * header.width;
 
+    // Verify this, as this is used to write into the memory of the QImage
+    if (pixel_count > img.sizeInBytes() / sizeof(QRgb)) {
+        qWarning() << "Invalid pixel count!" << pixel_count << "bytes available:" << img.sizeInBytes();
+        return false;
+    }
+
     QRgb *image_data = reinterpret_cast<QRgb*>(img.bits());
 
     if (!image_data) {
@@ -276,6 +286,11 @@ bool PSDHandler::canRead(QIODevice *device)
 
     char head[4];
     qint64 readBytes = device->read(head, sizeof(head));
+    if (readBytes < 0) {
+        qWarning() << "Read failed" << device->errorString();
+        return false;
+    }
+
     if (readBytes != sizeof(head)) {
         if (device->isSequential()) {
             while (readBytes > 0) {