fortify-headers

commit c2bb9e106a32619726cfc5052a1509e96b90de9f
parent c7e82d4863992c2f3bbb6f5a31fa8e5fd0e1643f
Author: Natanael Copa <ncopa@alpinelinux.org>
Date:   Thu,  7 May 2015 14:50:03 +0200

fix realpath when stdlib.h is included before limits.h

If program includes stdlib.h before limits.h without _XOPEN_SOURCE,
_GNU_SOURCE or _BSD_SOURCE explicitly set, then will it always trigger
the trap with musl libc.

This is becase stdlib.h will pull in features.h which will set
_GNU_SOURCE. This means that the fortify stdlib.h will not include
limits.h but it will still trigger the fortified realpath(), but without
PATH_MAX set.

We fix this by including system stdlib.h before testing if limits.h
should be included.

Since PATH_MAX is known at compile time we can also error at compile
time, instead of compiling a broken realpath().

Diffstat:
M
include/stdlib.h
 | 
6
+++---

1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/stdlib.h b/include/stdlib.h
@@ -1,12 +1,12 @@
 #ifndef _FORTIFY_STDLIB_H
 #define _FORTIFY_STDLIB_H
 
+#include_next <stdlib.h>
+
 #if defined(_XOPEN_SOURCE) || defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
 #include_next <limits.h>
 #endif
 
-#include_next <stdlib.h>
-
 #if defined(_FORTIFY_SOURCE) && _FORTIFY_SOURCE > 0 && defined(__OPTIMIZE__) && __OPTIMIZE__ > 0
 
 #ifdef __cplusplus
@@ -23,7 +23,7 @@ char *realpath(const char *path, char *resolved)
 
 	if (resolved) {
 #ifndef PATH_MAX
-		__builtin_trap();
+# error PATH_MAX unset. A fortified realpath will not work.
 #else
 		bos = __builtin_object_size(resolved, 0);
 		if (PATH_MAX > bos)