Make QVarLengthArray exception safe in case of OOM

After a exception is thrown in resize(), QVarLengthArray has an
invalid state with ptr == 0. On the next resize call when malloc
returns a valid pointer, oldPtr is 0 and it could crash in
memcpy because the pointer to the source is 0.
The patch ensures the valid pointer isn't overwritten with NULL.
When exceptions are disabled the user must ensure that malloc will
not fail.

Change-Id: Id12a5e3e1eacc551e4d1b64cba8e8414cfebd6e1
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 22 insertions, 26 deletions

diff --git a/src/corelib/tools/qvarlengtharray.h b/src/corelib/tools/qvarlengtharray.h
index a6c95e0cb7..90b10a3ed1 100644
--- a/src/corelib/tools/qvarlengtharray.h
+++ b/src/corelib/tools/qvarlengtharray.h
@@ -252,35 +252,31 @@ Q_OUTOFLINE_TEMPLATE void QVarLengthArray<T, Prealloc>::realloc(int asize, int a
 
     const int copySize = qMin(asize, osize);
     if (aalloc != a) {
-        ptr = reinterpret_cast<T *>(malloc(aalloc * sizeof(T)));
-        Q_CHECK_PTR(ptr);
-        if (ptr) {
-            s = 0;
-            a = aalloc;
-
-            if (QTypeInfo<T>::isStatic) {
-                QT_TRY {
-                    // copy all the old elements
-                    while (s < copySize) {
-                        new (ptr+s) T(*(oldPtr+s));
-                        (oldPtr+s)->~T();
-                        s++;
-                    }
-                } QT_CATCH(...) {
-                    // clean up all the old objects and then free the old ptr
-                    int sClean = s;
-                    while (sClean < osize)
-                        (oldPtr+(sClean++))->~T();
-                    if (oldPtr != reinterpret_cast<T *>(array) && oldPtr != ptr)
-                        free(oldPtr);
-                    QT_RETHROW;
+        T* newPtr = reinterpret_cast<T *>(malloc(aalloc * sizeof(T)));
+        Q_CHECK_PTR(newPtr); // could throw
+        // by design: in case of QT_NO_EXCEPTIONS malloc must not fail or it crashes here
+        ptr = newPtr;
+        s = 0;
+        a = aalloc;
+        if (QTypeInfo<T>::isStatic) {
+            QT_TRY {
+                // copy all the old elements
+                while (s < copySize) {
+                    new (ptr+s) T(*(oldPtr+s));
+                    (oldPtr+s)->~T();
+                    s++;
                 }
-            } else {
-                memcpy(ptr, oldPtr, copySize * sizeof(T));
+            } QT_CATCH(...) {
+                // clean up all the old objects and then free the old ptr
+                int sClean = s;
+                while (sClean < osize)
+                    (oldPtr+(sClean++))->~T();
+                if (oldPtr != reinterpret_cast<T *>(array) && oldPtr != ptr)
+                    free(oldPtr);
+                QT_RETHROW;
             }
         } else {
-            ptr = oldPtr;
-            return;
+            memcpy(ptr, oldPtr, copySize * sizeof(T));
         }
     }
     s = copySize;