qoi: fix buffer overflow kf5

Backport of MR !167:
- fix buffer overflow with corrupted images without image data
- fix unable to read very small images (e.g. 1x1 px)
- new test cases added
- detect incomplete files by checking the end of streams as written in the specs

src/imageformats/qoi.cpp

@@ -26,6 +26,7 @@ namespace // Private
 
 #define QOI_MAGIC (((unsigned int)'q') << 24 | ((unsigned int)'o') << 16 | ((unsigned int)'i') << 8 | ((unsigned int)'f'))
 #define QOI_HEADER_SIZE 14
+#define QOI_END_STREAM_PAD 8
 
 struct QoiHeader {
     quint32 MagicNumber;
@@ -62,6 +63,10 @@ static bool IsSupported(const QoiHeader &head)
     if (head.Width == 0 || head.Height == 0 || head.Channels < 3 || head.Colorspace > 1) {
         return false;
     }
+    // Set a reasonable upper limit
+    if (head.Width > 300000 || head.Height > 300000) {
+        return false;
+    }
     return true;
 }
 
@@ -94,7 +99,12 @@ static bool LoadQOI(QIODevice *device, const QoiHeader &qoi, QImage &img)
         255,
     };
 
-    quint64 px_len = quint64(qoi.Width) * qoi.Channels * 3 / 2;
+    // The px_len should be enough to read a complete "compressed" row: an uncompressible row can become
+    // larger than the row itself. It should never be more than 1/3 (RGB) or 1/4 (RGBA) the length of the
+    // row itself (see test bnm_rgb*.qoi) so I set the extra data to 1/2.
+    // The minimum value is to ensure that enough bytes are read when the image is very small (e.g. 1x1px):
+    // it can be set as large as you like.
+    quint64 px_len = std::max(quint64(1024), quint64(qoi.Width) * qoi.Channels * 3 / 2);
     if (px_len > kMaxQVectorSize) {
         return false;
     }
@@ -120,10 +130,14 @@ static bool LoadQOI(QIODevice *device, const QoiHeader &qoi, QImage &img)
             ba.append(device->read(px_len));
         }
 
-        quint64 chunks_len = ba.size() - 8; // 8 is the size of the QOI padding
+        if (ba.size() < QOI_END_STREAM_PAD) {
+            return false;
+        }
+
+        quint64 chunks_len = ba.size() - QOI_END_STREAM_PAD;
         quint64 p = 0;
         QRgb *scanline = (QRgb *)img.scanLine(y);
-        quint8 *input = reinterpret_cast<quint8 *>(ba.data());
+        const quint8 *input = reinterpret_cast<const quint8 *>(ba.constData());
         for (quint32 x = 0; x < qoi.Width; ++x) {
             if (run > 0) {
                 run--;
@@ -165,7 +179,10 @@ static bool LoadQOI(QIODevice *device, const QoiHeader &qoi, QImage &img)
         }
     }
 
-    return true;
+    // From specs the byte stream's end is marked with 7 0x00 bytes followed by a single 0x01 byte.
+    // NOTE: Instead of using "ba == QByteArray::fromRawData("\x00\x00\x00\x00\x00\x00\x00\x01", 8)"
+    //       we preferred a generic check that allows data to exist after the end of the file.
+    return (ba.startsWith(QByteArray::fromRawData("\x00\x00\x00\x00\x00\x00\x00\x01", 8)));
 }
 
 } // namespace