mmap: check ->vm_ops before dereferencing

Check whether the VMA has a vm_ops before calling close, just
like we check vm_ops before calling open a few dozen lines
higher up in the function.
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/mmap.c

@@ -1977,6 +1977,7 @@ static int __split_vma(struct mm_struct * mm, struct vm_area_struct * vma,
 		return 0;
 
 	/* Clean everything up if vma_adjust failed. */
+	if (new->vm_ops && new->vm_ops->close)
 		new->vm_ops->close(new);
 	if (new->vm_file) {
 		if (vma->vm_flags & VM_EXECUTABLE)