Introduce a settable allocation limit on image loading

[ChangeLog][QtGui][QImageReader] Introduced a settable allocation
limit on image loading to limit resource usage from corrupt image
files.

Change-Id: Ibed7b0cac32798125a060e6db80b17ebc5e70759
Task-number: QTBUG-85037
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

src/gui/image/qimageiohandler.cpp

@@ -264,9 +264,10 @@
 */
 
 #include "qimageiohandler.h"
+#include "qimage_p.h"
 
 #include <qbytearray.h>
-#include <qimage.h>
+#include <qimagereader.h>
 #include <qvariant.h>
 
 QT_BEGIN_NAMESPACE
@@ -552,6 +553,45 @@ int QImageIOHandler::nextImageDelay() const
     return 0;
 }
 
+/*!
+    \since 6.0
+
+    This is a convenience method for the reading function in subclasses. Image
+    format handlers must reject loading an image if the required allocation
+    would exceeed the current allocation limit. This function checks the
+    parameters and limit, and does the allocation if it is valid and required.
+    Upon successful return, \a image will be a valid, detached QImage of the
+    given \a size and \a format.
+
+    \sa QImageReader::allocationLimit()
+*/
+bool QImageIOHandler::allocateImage(QSize size, QImage::Format format, QImage *image)
+{
+    Q_ASSERT(image);
+    if (size.isEmpty() || format <= QImage::Format_Invalid || format >= QImage::NImageFormats)
+        return false;
+
+    if (image->size() == size && image->format() == format) {
+        image->detach();
+    } else {
+        if (const int mbLimit = QImageReader::allocationLimit()) {
+            qsizetype depth = qt_depthForFormat(format);
+            QImageData::ImageSizeParameters szp =
+                    QImageData::calculateImageParameters(size.width(), size.height(), depth);
+            if (!szp.isValid())
+                return false;
+            const qsizetype mb = szp.totalSize >> 20;
+            if (mb > mbLimit || (mb == mbLimit && szp.totalSize % (1 << 20))) {
+                qWarning("QImageIOHandler: Rejecting image as it exceeds the current "
+                         "allocation limit of %i megabytes", mbLimit);
+                return false;
+            }
+        }
+        *image = QImage(size, format);
+    }
+    return !image->isNull();
+}
+
 #ifndef QT_NO_IMAGEFORMATPLUGIN
 
 /*!

src/gui/image/qimageiohandler.h

@@ -41,6 +41,7 @@
 #define QIMAGEIOHANDLER_H
 
 #include <QtGui/qtguiglobal.h>
+#include <QtGui/qimage.h>
 #include <QtCore/qiodevice.h>
 #include <QtCore/qplugin.h>
 #include <QtCore/qfactoryinterface.h>
@@ -123,6 +124,8 @@ public:
     virtual int currentImageNumber() const;
     virtual QRect currentImageRect() const;
 
+    static bool allocateImage(QSize size, QImage::Format format, QImage *image);
+
 protected:
     QImageIOHandler(QImageIOHandlerPrivate &dd);
     QScopedPointer<QImageIOHandlerPrivate> d_ptr;

src/gui/image/qimagereader.cpp

@@ -492,8 +492,12 @@ public:
     QString errorString;
 
     QImageReader *q;
+
+    static int maxAlloc;
 };
 
+int QImageReaderPrivate::maxAlloc = 128; // 128 MB is enough for an 8K 32bpp image
+
 /*!
     \internal
 */
@@ -1575,4 +1579,34 @@ QList<QByteArray> QImageReader::imageFormatsForMimeType(const QByteArray &mimeTy
                                                               QImageReaderWriterHelpers::CanRead);
 }
 
+/*!
+    \since 6.0
+
+    Returns the current allocation limit, in megabytes.
+
+    \sa setAllocationLimit()
+*/
+int QImageReader::allocationLimit()
+{
+    return QImageReaderPrivate::maxAlloc;
+}
+
+/*!
+    \since 6.0
+
+    Sets the allocation limit to \a mbLimit megabytes. Images that would
+    require a QImage memory allocation above this limit will be rejected.
+
+    This limit helps applications avoid unexpectedly large memory usage from
+    loading corrupt image files. It is normally not needed to change it. The
+    default limit is large enough for all commonly used image sizes.
+
+    \sa allocationLimit()
+*/
+void QImageReader::setAllocationLimit(int mbLimit)
+{
+    if (mbLimit >= 0)
+        QImageReaderPrivate::maxAlloc = mbLimit;
+}
+
 QT_END_NAMESPACE

src/gui/image/qimagereader.h

@@ -142,6 +142,8 @@ public:
     static QList<QByteArray> supportedImageFormats();
     static QList<QByteArray> supportedMimeTypes();
     static QList<QByteArray> imageFormatsForMimeType(const QByteArray &mimeType);
+    static int allocationLimit();
+    static void setAllocationLimit(int mbLimit);
 
 private:
     Q_DISABLE_COPY(QImageReader)