From a3b753c2d077313fc9eb93af547051b956e383fc Mon Sep 17 00:00:00 2001
From: Eirik Aavitsland <eirik.aavitsland@qt.io>
Date: Mon, 25 Oct 2021 14:17:55 +0200
Subject: [PATCH] Do stricter error checking when parsing path nodes
MIME-Version: 1.0
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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>
---
 src/svg/qsvghandler.cpp | 59 +++++++++++++++++------------------------
 1 file changed, 25 insertions(+), 34 deletions(-)

diff --git a/src/svg/qsvghandler.cpp b/src/svg/qsvghandler.cpp
index 08ee7819..db21d5f4 100644
--- a/src/svg/qsvghandler.cpp
+++ b/src/svg/qsvghandler.cpp
@@ -1611,6 +1611,7 @@ static void pathArc(QPainterPath &path,
 
 static bool parsePathDataFast(const QStringRef &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;
@@ -1618,7 +1619,8 @@ static bool parsePathDataFast(const QStringRef &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;
         QChar pathElem = *str;
@@ -1632,14 +1634,13 @@ static bool parsePathDataFast(const QStringRef &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;
@@ -1656,8 +1657,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
                 break;
             case 'M': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = x0 = num[0];
@@ -1683,8 +1683,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
                 break;
             case 'l': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0] + offsetX;
@@ -1697,8 +1696,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
                 break;
             case 'L': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0];
@@ -1738,8 +1736,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
                 break;
             case 'c': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0] + offsetX, num[1] + offsetY);
@@ -1755,8 +1752,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'C': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0], num[1]);
@@ -1772,8 +1768,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 's': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1794,8 +1789,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'S': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1816,8 +1810,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0] + offsetX, num[1] + offsetY);
@@ -1832,8 +1825,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'Q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0], num[1]);
@@ -1848,8 +1840,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 't': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0] + offsetX, num[1] + offsetY);
@@ -1869,8 +1860,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'T': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0], num[1]);
@@ -1890,8 +1880,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
             }
             case 'a': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1913,8 +1902,7 @@ static bool parsePathDataFast(const QStringRef &dataStr, QPainterPath &path)
                 break;
             case 'A': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1935,12 +1923,15 @@ static bool parsePathDataFast(const QStringRef &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,
@@ -2976,8 +2967,8 @@ 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;


