security hardening: ensure suid programs have valid stdin/out/err

this behavior (opening fds 0-2 for a suid program) is explicitly
allowed (but not required) by POSIX to protect badly-written suid
programs from clobbering files they later open.

this commit does add some cost in startup code, but the availability
of auxv and the security flag will be useful elsewhere in the future.
in particular auxv is needed for static-linked vdso support, which is
still waiting to be committed (sorry nik!)

1 files changed, 4 insertions, 2 deletions

diff --git a/src/internal/libc.h b/src/internal/libc.h
index 115cd865..d985902c 100644
--- a/src/internal/libc.h
+++ b/src/internal/libc.h
@@ -7,13 +7,15 @@
 struct __libc {
 	void *main_thread;
 	int threaded;
-	int canceldisable;
+	int secure;
+	size_t *auxv;
 	int (*atexit)(void (*)(void));
 	void (*fini)(void);
 	void (*ldso_fini)(void);
 	volatile int threads_minus_1;
-	int ofl_lock;
+	int canceldisable;
 	FILE *ofl_head;
+	int ofl_lock;
 };