diff options
author | Kevin Funk <kfunk@kde.org> | 2014-06-27 13:49:55 +0200 |
---|---|---|
committer | Kevin Funk <kevin.funk@kdab.com> | 2014-07-09 00:23:53 +0200 |
commit | e112c2ee20f89f288a4f0a13827f0b64067096f0 (patch) | |
tree | 1e7612d5993a96d68c254826863113c690b0df40 /src/corelib | |
parent | 01cc6254068b96a155ac9376458dd4580c7c7b0b (diff) |
Make QExplicitlySharedDataPointer<T> copy-ctor from QESDP<X> more safe
With "QExplicitlySharedDataPointer::QExplicitlySharedDataPointer( const
QExplicitlySharedDataPointer<X> & other)" implicitly doing an
static_cast<T *>(...) on other.data(), this could lead to dangerous use
of this copy constructor.
Example code:
QExplicitlySharedDataPointer<Base> base(new Base);
QExplicitlySharedDataPointer<Derived> derived(base); // that works!
This patchs disables the use of the static_cast, and adds a new define called
QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST to re-enable
that code path.
Note, that the other way-around (assigning 'derived' to 'base') still
works as intended.
Other side note: QtXmlPatterns is relying heavily on the hidden
static_cast "feature". The other default Qt modules compile fine with
the static_cast removed.
[ChangeLog][Important Behavior Changes] QExplicitelySharedDataPointer's
copy constructor which performs a static_cast from "X *" to "T *"
(when constructing a QExplicitlySharedDataPointer<T> from
a QExplicitlySharedDataPointer<X>) doesn't perform a static_cast
from "X *" to "T *" any more. Instead, an implicit cast is now
performed. This change will break compilation of code that
relied on the downcast (i.e. cast towards a more derived type) of the
templated type when copy costructing a QExplicitelySharedDataPointer
object. Please refer to the class documentation for more information
about this issue and a workaround to keep old code compiling.
Change-Id: Id32aba6cda4e6d44728d7bc3a5c0c7a20f19adc6
Reviewed-by: Kevin Funk <kevin.funk@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Diffstat (limited to 'src/corelib')
-rw-r--r-- | src/corelib/tools/qshareddata.cpp | 32 | ||||
-rw-r--r-- | src/corelib/tools/qshareddata.h | 7 |
2 files changed, 34 insertions, 5 deletions
diff --git a/src/corelib/tools/qshareddata.cpp b/src/corelib/tools/qshareddata.cpp index 941e58ee7c..b5eed0f504 100644 --- a/src/corelib/tools/qshareddata.cpp +++ b/src/corelib/tools/qshareddata.cpp @@ -538,10 +538,34 @@ QT_BEGIN_NAMESPACE /*! \fn QExplicitlySharedDataPointer::QExplicitlySharedDataPointer(const QExplicitlySharedDataPointer<X>& other) This copy constructor is different in that it allows \a other to be a different type of explicitly shared data pointer but one that has - a compatible shared data object. It performs a static cast of the - \e{d pointer} in \a other and sets the \e {d pointer} of \e this to - the converted \e{d pointer}. It increments the reference count of - the shared data object. + a compatible shared data object. + + By default, the \e{d pointer} of \a other (of type \c{X *}) gets + implicitly converted to the type \c{T *}; the result of this + conversion is set as the \e{d pointer} of \e{this}, and the + reference count of the shared data object is incremented. + + However, if the macro + \c{QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST} is defined + before including the \c{QExplicitlySharedDataPointer} header, then + the \e{d pointer} of \a other undergoes a \c{static_cast} to the + type \c{T *}. The result of the cast is then set as the + \e{d pointer} of \e{this}, and the reference count of the shared data + object is incremented. + + \warning relying on such \c{static_cast} is potentially dangerous, + because it allows code like this to compile: + + \code + QExplicitlySharedDataPointer<Base> base(new Base); + QExplicitlySharedDataPointer<Derived> derived(base); // !!! DANGER !!! + \endcode + + Starting from Qt 5.4 the cast is disabled by default. It is + possible to enable it back by defining the + \c{QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST} macro, and + therefore to allow old code (that relied on this feature) to + compile without modifications. */ /*! \fn QExplicitlySharedDataPointer<T>& QExplicitlySharedDataPointer::operator=(const QExplicitlySharedDataPointer<T>& other) diff --git a/src/corelib/tools/qshareddata.h b/src/corelib/tools/qshareddata.h index 415ea0d6c7..d85184e995 100644 --- a/src/corelib/tools/qshareddata.h +++ b/src/corelib/tools/qshareddata.h @@ -167,7 +167,12 @@ public: inline QExplicitlySharedDataPointer(const QExplicitlySharedDataPointer<T> &o) : d(o.d) { if (d) d->ref.ref(); } template<class X> - inline QExplicitlySharedDataPointer(const QExplicitlySharedDataPointer<X> &o) : d(static_cast<T *>(o.data())) + inline QExplicitlySharedDataPointer(const QExplicitlySharedDataPointer<X> &o) +#ifdef QT_ENABLE_QEXPLICITLYSHAREDDATAPOINTER_STATICCAST + : d(static_cast<T *>(o.data())) +#else + : d(o.data()) +#endif { if(d) d->ref.ref(); |