File 0002-qDecodeDataUrl-fix-precondition-violation-in-call-to.patch of Package qt6-base.40448

From 21cd27b3b9973f43df152a1dd9dadbbf905c6a73 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Fri, 25 Apr 2025 13:58:25 +0200
Subject: [PATCH] qDecodeDataUrl(): fix precondition violation in call to QByteArrayView::at()

It is a precondition violation to call QByteArrayView::at() with
size() as argument. The code used that, though, as an implicit
end-of-string check, assuming == ' ' and == '=' would both fail for
null bytes. Besides, QByteArrays (but most certainly QByteArrayViews)
need not be null-terminated, so this could read even past size().

To fix, use higher-level API (startsWith()), consuming parsed tokens
along the way.

Add a test that would crash in debug mode before the fix.

Amends the start of the public history.

[ChangeLog][QtCore] Fixed a bug in the handling of data: URLs that
could lead to a crash if Qt was built with assertions enabled. This
affects QNetworkManager and links in QTextDocument.

Pick-to: 6.8 6.5 6.5.9 6.2 5.15
Change-Id: I4331c88051dfbb0a18fe7da4f50858c707785d09
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
(cherry picked from commit 4d839093b480d30eef8a89c0f864ee3f340adaa1)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
---

diff --git a/src/corelib/io/qdataurl.cpp b/src/corelib/io/qdataurl.cpp
index 65b934b..c5ecca8 100644
--- a/src/corelib/io/qdataurl.cpp
+++ b/src/corelib/io/qdataurl.cpp
@@ -47,10 +47,10 @@
#         QLatin1StringView textPlain;
#         constexpr auto charset = "charset"_L1;
#         if (QLatin1StringView{data}.startsWith(charset, Qt::CaseInsensitive)) {
         }
 
         if (QLatin1StringView{data}.startsWith("charset"_L1, Qt::CaseInsensitive)) {
#-            qsizetype i = charset.size();
-            qsizetype i = 7;      // strlen("charset")
-            while (data.at(i) == ' ')
-                ++i;
-            if (data.at(i) == '=')
#+            QByteArrayView copy = data.sliced(charset.size());
+            QByteArrayView copy = data.sliced(7);
+            while (copy.startsWith(' '))
+                copy.slice(1);
+            if (copy.startsWith('='))
#                 textPlain = "text/plain;"_L1;
                 data.prepend("text/plain;");
         }
 
diff --git a/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp b/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
index e694a79..943b168 100644
--- a/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
+++ b/tests/auto/corelib/io/qdataurl/tst_qdataurl.cpp
@@ -34,6 +34,8 @@
         "text/plain"_L1, QByteArray::fromPercentEncoding("%E2%88%9A"));
     row("everythingIsCaseInsensitive", "Data:texT/PlaiN;charSet=iSo-8859-1;Base64,SGVsbG8=", true,
         "texT/PlaiN;charSet=iSo-8859-1"_L1, QByteArrayLiteral("Hello"));
+    row("prematureCharsetEnd", "data:charset,", true,
+        "charset", ""); // nonsense result, but don't crash
 }
 
 void tst_QDataUrl::decode()