From cb1ce9e1815a492de0f13c2b046b8472024b9f6d Mon Sep 17 00:00:00 2001
From: jvoisin
Date: Wed, 14 Jun 2023 14:59:11 +0200
Subject: Add tests for strncpy and handle overlapping buffers there

---
 include/string.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

(limited to 'include/string.h')

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);
-- 
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