# HG changeset patch
# User Matt Mackall <mpm@selenic.com>
# Date 2012-05-12 08:02:47
# Node ID 9e40bc4c1bdee81f41be17c20174a2aa168f0db7
# Parent  fcb97d9a26cd25c9751062fc73f2ee43c7eb0f28

diffhelpers: harden testhunk

diff --git a/mercurial/diffhelpers.c b/mercurial/diffhelpers.c
--- a/mercurial/diffhelpers.c
+++ b/mercurial/diffhelpers.c
@@ -135,7 +135,7 @@ testhunk(PyObject *self, PyObject *args)
 		return NULL;
 	alen = PyList_Size(a);
 	blen = PyList_Size(b);
-	if (alen > blen - bstart) {
+	if (alen > blen - bstart || bstart < 0) {
 		return Py_BuildValue("l", -1);
 	}
 	for (i = 0; i < alen; i++) {