From 36cfd9efb9b22b891adee9c48d30202289cfa620 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
Pick-to: 6.2 5.15 5.12
Change-Id: Ic5e65d6b658516d6f1317c72de365c8c7ad81891
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
Reviewed-by: Robert Löhning <robert.loehning@qt.io>
---
 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 db29211..dd869ff 100644
--- a/src/svg/qsvghandler.cpp
+++ b/src/svg/qsvghandler.cpp
@@ -1615,6 +1615,7 @@ 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;
@@ -1622,7 +1623,8 @@ static bool parsePathDataFast(const QStr
     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;
@@ -1636,14 +1638,13 @@ static bool parsePathDataFast(const QStr
             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;
@@ -1660,8 +1661,7 @@ static bool parsePathDataFast(const QStr
                 break;
             case 'M': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = x0 = num[0];
@@ -1687,8 +1687,7 @@ static bool parsePathDataFast(const QStr
                 break;
             case 'l': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0] + offsetX;
@@ -1701,8 +1700,7 @@ static bool parsePathDataFast(const QStr
                 break;
             case 'L': {
                 if (count < 2) {
-                    num++;
-                    count--;
+                    ok = false;
                     break;
                 }
                 x = num[0];
@@ -1742,8 +1740,7 @@ static bool parsePathDataFast(const QStr
                 break;
             case 'c': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0] + offsetX, num[1] + offsetY);
@@ -1759,8 +1756,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'C': {
                 if (count < 6) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1(num[0], num[1]);
@@ -1776,8 +1772,7 @@ static bool parsePathDataFast(const QStr
             }
             case 's': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1798,8 +1793,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'S': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c1;
@@ -1820,8 +1814,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0] + offsetX, num[1] + offsetY);
@@ -1836,8 +1829,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'Q': {
                 if (count < 4) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF c(num[0], num[1]);
@@ -1852,8 +1844,7 @@ static bool parsePathDataFast(const QStr
             }
             case 't': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0] + offsetX, num[1] + offsetY);
@@ -1873,8 +1864,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'T': {
                 if (count < 2) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 QPointF e(num[0], num[1]);
@@ -1894,8 +1884,7 @@ static bool parsePathDataFast(const QStr
             }
             case 'a': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1917,8 +1906,7 @@ static bool parsePathDataFast(const QStr
                 break;
             case 'A': {
                 if (count < 7) {
-                    num += count;
-                    count = 0;
+                    ok = false;
                     break;
                 }
                 qreal rx = (*num++);
@@ -1939,12 +1927,15 @@ static bool parsePathDataFast(const QStr
             }
                 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,
@@ -2980,8 +2971,8 @@ static QSvgNode *createPathNode(QSvgNode
 
     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;

