Do stricter error checking when parsing path nodes

The SVG spec mandates that path parsing should terminate on the first
error encountered, and an error be reported. To improve the handling
of corrupt files, implement such error handling, and also limit the
number of QPainterPath elements to a reasonable range.

Fixes: QTBUG-96044
Change-Id: Ic5e65d6b658516d6f1317c72de365c8c7ad81891
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
(cherry picked from commit 36cfd9efb9b22b891adee9c48d30202289cfa620)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 25 insertions, 34 deletions

diff --git a/src/svg/qsvghandler.cpp b/src/svg/qsvghandler.cpp
index e6f304f..b665e5f 100644
--- a/src/svg/qsvghandler.cpp
+++ b/src/svg/qsvghandler.cpp
@@ -1597,6 +1597,7 @@ static void pathArc(QPainterPath &path,
 
 static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
 {
+    const int maxElementCount = 0x7fff; // Assume file corruption if more path elements than this
     qreal x0 = 0, y0 = 0;              // starting point
     qreal x = 0, y = 0;                // current point
     char lastMode = 0;
@@ -1604,7 +1605,8 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
     const QChar *str = dataStr.constData();
     const QChar *end = str + dataStr.size();
 
-    while (str != end) {
+    bool ok = true;
+    while (ok && str != end) {
         while (str->isSpace() && (str + 1) != end)
             ++str;
         QChar pathElem = *str;
@@ -1621,14 +1623,13 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             arg.append(0);//dummy
         const qreal *num = arg.constData();
         int count = arg.count();
-        while (count > 0) {
+        while (ok && count > 0) {
             qreal offsetX = x;        // correction offsets
             qreal offsetY = y;        // for relative commands
             switch (pathElem.unicode()) {
             case 'm': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = x0 = num[0] + offsetX;
@@ -1645,8 +1646,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
                 break;
             case 'M': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = x0 = num[0];
@@ -1672,8 +1672,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
                 break;
             case 'l': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0] + offsetX;
@@ -1686,8 +1685,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
                 break;
             case 'L': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0];
@@ -1727,8 +1725,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
                 break;
             case 'c': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0] + offsetX, num[1] + offsetY);
@@ -1744,8 +1741,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'C': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0], num[1]);
@@ -1761,8 +1757,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 's': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1783,8 +1778,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'S': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1805,8 +1799,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0] + offsetX, num[1] + offsetY);
@@ -1821,8 +1814,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'Q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0], num[1]);
@@ -1837,8 +1829,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 't': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0] + offsetX, num[1] + offsetY);
@@ -1858,8 +1849,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'T': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0], num[1]);
@@ -1879,8 +1869,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
             case 'a': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1902,8 +1891,7 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
                 break;
             case 'A': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1924,12 +1912,15 @@ static bool parsePathDataFast(QStringView dataStr, QPainterPath &path)
             }
                 break;
             default:
-                return false;
+                ok = false;
+                break;
             }
             lastMode = pathElem.toLatin1();
+            if (path.elementCount() > maxElementCount)
+                ok = false;
         }
     }
-    return true;
+    return ok;
 }
 
 static bool parseStyle(QSvgNode *node,
@@ -2987,8 +2978,8 @@ static QSvgNode *createPathNode(QSvgNode *parent,
 
     QPainterPath qpath;
     qpath.setFillRule(Qt::WindingFill);
-    //XXX do error handling
-    parsePathDataFast(data, qpath);
+    if (!parsePathDataFast(data, qpath))
+        qCWarning(lcSvgHandler, "Invalid path data; path truncated.");
 
     QSvgNode *path = new QSvgPath(parent, qpath);
     return path;