Add tests for strncpy and handle overlapping buffers there

1 files changed, 6 insertions, 1 deletions

diff --git a/include/string.h b/include/string.h
index 9b6e601..f416a51 100644
--- a/include/string.h
+++ b/include/string.h
@@ -156,8 +156,13 @@ __access (write_only, 1)
 __access (read_only, 2, 3)
 _FORTIFY_FN(strncpy) char *strncpy(char *__d, const char *__s, size_t __n)
 {
-        size_t __b = __bos(__d, 0);
+        /* trap if pointers are overlapping but not if dst == src.
+         * gcc seems to like to generate code that relies on dst == src */
+        if ((__d < __s && __d + __n > __s) ||
+            (__s < __d && __s + __n > __d))
+                __builtin_trap();
 
+        size_t __b = __bos(__d, 0);
         if (__n > __b)
                 __builtin_trap();
         return __orig_strncpy(__d, __s, __n);