fortify-headers

commit ff82ffbc74d82091527449e31fe351d15830f716
parent 1435d8186b1954de640ec79717c5e564243bd350
Author: info@mobile-stream.com <info@mobile-stream.com>
Date:   Wed,  6 Mar 2019 16:28:48 +0300

realpath: guard slow/trap path with PATH_MAX

This allows the compiler to optimize out the slow/trap path at all
for the typical correct code:

char buf[PATH_MAX];
r = realpath(path, buf);

The change keeps the "unknown object size" case handling intact.

Diffstat:
M
include/stdlib.h
 | 
8
+++-----

1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/include/stdlib.h b/include/stdlib.h
@@ -39,12 +39,10 @@ extern "C" {
 #undef realpath
 _FORTIFY_FN(realpath) char *realpath(const char *__p, char *__r)
 {
-	size_t __b = __builtin_object_size(__r, 0);
-
-	if (__r) {
 #ifndef PATH_MAX
 #error PATH_MAX unset. A fortified realpath will not work.
 #else
+	if (__r && PATH_MAX > __builtin_object_size(__r, 2)) {
 		char __buf[PATH_MAX], *__ret;
 		size_t __l;
 
@@ -52,13 +50,13 @@ _FORTIFY_FN(realpath) char *realpath(const char *__p, char *__r)
 		if (!__ret)
 			return NULL;
 		__l = __builtin_strlen(__ret) + 1;
-		if (__l > __b)
+		if (__l > __builtin_object_size(__r, 0))
 			__builtin_trap();
 		__builtin_memcpy(__r, __ret, __l);
 		return __r;
-#endif
 	}
 	return __orig_realpath(__p, __r);
+#endif
 }
 #endif