Bounds-check time-zone offsets when parsing

Parsing of time-zone offsets should check the offset string conforms
to the expected format and has valid values in its fields. The
QDateTime parser, fromOffsetString(), neglected the bounds check on
hours; the QTzTimeZonePrivate parser, parsePosixTime(), neglected all
upper bounds checks, only checking against negative valus.

Drive-by - refined phrasing of a comment.

Fixes: QTBUG-88656
Change-Id: If04cdbe65064108eaa87c42310527783ad21b4c0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit 380d97e1bd15e753907c378a070bdf7f1c1cf06e)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/time/qdatetime.cpp

@@ -319,7 +319,7 @@ static int fromOffsetString(QStringView offsetString, bool *valid) noexcept
     const QStringView hhRef = time.first(qMin(hhLen, time.size()));
     bool ok = false;
     const int hour = hhRef.toInt(&ok);
-    if (!ok)
+    if (!ok || hour > 23) // More generous than QTimeZone::MaxUtcOffsetSecs
         return 0;
 
     const QStringView mmRef = time.sliced(qMin(mmIndex, time.size()));

src/corelib/time/qtimezoneprivate_tz.cpp

@@ -395,29 +395,34 @@ static int parsePosixTime(const char *begin, const char *end)
     // Format "hh[:mm[:ss]]"
     int hour, min = 0, sec = 0;
 
-    // Note that the calls to qstrtoll do *not* check the end pointer, which
+    // Note that the calls to qstrtoll do *not* check against the end pointer,
-    // means they proceed until they find a non-digit. We check that we're
+    // which means they proceed until they find a non-digit. We check that we're
-    // still in range at the end, but we may have read from past end. It's the
+    // still in range at the end, but we may have read past end. It's the
-    // caller's responsibility to ensure that begin is part of a
+    // caller's responsibility to ensure that begin is part of a null-terminated
-    // null-terminated string.
+    // string.
 
+    const int maxHour = QTimeZone::MaxUtcOffsetSecs / 3600;
     bool ok = false;
-    hour = qstrtoll(begin, &begin, 10, &ok);
+    const char *cut = begin;
-    if (!ok || hour < 0)
+    hour = qstrtoll(begin, &cut, 10, &ok);
+    if (!ok || hour < 0 || hour > maxHour || cut > begin + 2)
         return INT_MIN;
+    begin = cut;
     if (begin < end && *begin == ':') {
         // minutes
         ++begin;
-        min = qstrtoll(begin, &begin, 10, &ok);
+        min = qstrtoll(begin, &cut, 10, &ok);
-        if (!ok || min < 0)
+        if (!ok || min < 0 || min > 59 || cut > begin + 2)
             return INT_MIN;
 
+        begin = cut;
         if (begin < end && *begin == ':') {
             // seconds
             ++begin;
-            sec = qstrtoll(begin, &begin, 10, &ok);
+            sec = qstrtoll(begin, &cut, 10, &ok);
-            if (!ok || sec < 0)
+            if (!ok || sec < 0 || sec > 59 || cut > begin + 2)
                 return INT_MIN;
+            begin = cut;
         }
     }