Avoid calling internal libc function through PLT or accessing data

though GOT, by staticizing and hiding.  Add setter for
__error_selector to hide it as well.

Suggested and reviewed by:	jilles
Sponsored by:	The FreeBSD Foundation
MFC after:	1 week

3 files changed, 14 insertions, 7 deletions

diff --git a/lib/libc/include/libc_private.h b/lib/libc/include/libc_private.h
index adf342d..ea1a97b 100644
--- a/lib/libc/include/libc_private.h
+++ b/lib/libc/include/libc_private.h
@@ -173,13 +173,13 @@ typedef pthread_func_t pthread_func_entry_t[2];
 
 extern pthread_func_entry_t __thr_jtable[];
 
-extern int *(*__error_selector)(void);
+void	__set_error_selector(int *(*arg)(void));
 int	_pthread_mutex_init_calloc_cb_stub(pthread_mutex_t *mutex,
 	    void *(calloc_cb)(__size_t, __size_t));
 
 typedef int (*interpos_func_t)(void);
 interpos_func_t *__libc_interposing_slot(int interposno);
-extern interpos_func_t __libc_interposing[];
+extern interpos_func_t __libc_interposing[] __hidden;
 
 enum {
 	INTERPOS_accept,
diff --git a/lib/libc/sys/Symbol.map b/lib/libc/sys/Symbol.map
index 7d82361..f1f57ba 100644
--- a/lib/libc/sys/Symbol.map
+++ b/lib/libc/sys/Symbol.map
@@ -1045,8 +1045,7 @@ FBSDprivate_1.0 {
 	__sys_write;
 	_writev;
 	__sys_writev;
-	__error_unthreaded;
-	__error_selector;
+	__set_error_selector;
 	nlm_syscall;
 	gssd_syscall;
 	__libc_interposing_slot;
diff --git a/lib/libc/sys/__error.c b/lib/libc/sys/__error.c
index 329d124..28cc31d 100644
--- a/lib/libc/sys/__error.c
+++ b/lib/libc/sys/__error.c
@@ -32,13 +32,21 @@ __FBSDID("$FreeBSD$");
 
 extern int errno;
 
-int *
+static int *
 __error_unthreaded(void)
 {
-	return(&errno);
+
+	return (&errno);
 }
 
-int *(*__error_selector)(void) = __error_unthreaded;
+static int *(*__error_selector)(void) = __error_unthreaded;
+
+void
+__set_error_selector(int *(*arg)(void))
+{
+
+	__error_selector = arg;
+}
 
 int *
 __error(void)