Add a check for overlapping copies in strcpy

1 files changed, 8 insertions, 1 deletions

diff --git a/include/string.h b/include/string.h
index f08eb4c..8685bb7 100644
--- a/include/string.h
+++ b/include/string.h
@@ -107,8 +107,15 @@ _FORTIFY_FN(strcat) char *strcat(char *__d, const char *__s)
 
 _FORTIFY_FN(strcpy) char *strcpy(char *__d, const char *__s)
 {
-        size_t __b = __bos(__d, 0);
+        size_t __n = strlen(__s) + 1;
+
+        /* 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 (strlen(__s) + 1 > __b)
                 __builtin_trap();
         return __orig_strcpy(__d, __s);