libc: Always use our own copy of sys_errlist and sys_nerr (.so only).

This ensures strerror() and friends continue to work correctly even if a
(non-PIE) executable linked against an older libc imports sys_errlist (which
causes sys_errlist to refer to the executable's copy with a size fixed when
that executable was linked).

The executable's use of sys_errlist remains broken because it uses the
current value of sys_nerr and may access past the bounds of the array.

Different from the message "Using sys_errlist from executables is not
ABI-stable" on freebsd-arch, this change does not affect the static library.
There seems no reason to prevent overriding the error messages in the static
library.

4 files changed, 56 insertions, 4 deletions

diff --git a/lib/libc/gen/errlst.c b/lib/libc/gen/errlst.c
index 7b4fd62..f8fe968 100644
--- a/lib/libc/gen/errlst.c
+++ b/lib/libc/gen/errlst.c
@@ -34,6 +34,7 @@ static char sccsid[] = "@(#)errlst.c	8.2 (Berkeley) 11/16/93";
 __FBSDID("$FreeBSD$");
 
 #include <stdio.h>
+#include "errlst.h"
 
 const char *const sys_errlist[] = {
 	"No error: 0",				/*  0 - ENOERROR */
@@ -156,3 +157,8 @@ const char *const sys_errlist[] = {
 	"Previous owner died",			/* 96 - EOWNERDEAD */
 };
 const int sys_nerr = sizeof(sys_errlist) / sizeof(sys_errlist[0]);
+
+#ifdef PIC
+__strong_reference(sys_errlist, __hidden_sys_errlist);
+__strong_reference(sys_nerr, __hidden_sys_nerr);
+#endif
diff --git a/lib/libc/include/errlst.h b/lib/libc/include/errlst.h
new file mode 100644
index 0000000..4e9e29f
--- /dev/null
+++ b/lib/libc/include/errlst.h
@@ -0,0 +1,43 @@
+/*-
+ * Copyright (c) 2013 Jilles Tjoelker
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD$
+ */
+
+#ifndef __ERRLST_H__
+#define __ERRLST_H__
+
+#include <sys/cdefs.h>
+
+#ifdef PIC
+/* If the main executable imports these, do not use its copy from libc.so. */
+extern const char *const __hidden_sys_errlist[] __hidden;
+extern const int __hidden_sys_nerr __hidden;
+#else
+#define __hidden_sys_errlist sys_errlist
+#define __hidden_sys_nerr sys_nerr
+#endif
+
+#endif /* __ERRLST_H__ */
diff --git a/lib/libc/stdio/xprintf_errno.c b/lib/libc/stdio/xprintf_errno.c
index 0c2be46..3c831d1 100644
--- a/lib/libc/stdio/xprintf_errno.c
+++ b/lib/libc/stdio/xprintf_errno.c
@@ -34,6 +34,7 @@
 #include <vis.h>
 #include <assert.h>
 #include <sys/time.h>
+#include "errlst.h"
 #include "printf.h"
 
 int
@@ -54,7 +55,7 @@ __printf_render_errno(struct __printf_io *io, const struct printf_info *pi __unu
 
 	ret = 0;
 	error = *((const int *)arg[0]);
-	if (error >= 0 && error < sys_nerr) {
+	if (error >= 0 && error < __hidden_sys_nerr) {
 		p = strerror(error);
 		return (__printf_out(io, pi, p, strlen(p)));
 	}
diff --git a/lib/libc/string/strerror.c b/lib/libc/string/strerror.c
index e11b351..1d7a385 100644
--- a/lib/libc/string/strerror.c
+++ b/lib/libc/string/strerror.c
@@ -42,6 +42,8 @@ __FBSDID("$FreeBSD$");
 #include <string.h>
 #include <stdio.h>
 
+#include "errlst.h"
+
 #define	UPREFIX		"Unknown error"
 
 /*
@@ -87,7 +89,7 @@ strerror_r(int errnum, char *strerrbuf, size_t buflen)
 	catd = catopen("libc", NL_CAT_LOCALE);
 #endif
 
-	if (errnum < 0 || errnum >= sys_nerr) {
+	if (errnum < 0 || errnum >= __hidden_sys_nerr) {
 		errstr(errnum,
 #if defined(NLS)
 			catgets(catd, 1, 0xffff, UPREFIX),
@@ -99,9 +101,9 @@ strerror_r(int errnum, char *strerrbuf, size_t buflen)
 	} else {
 		if (strlcpy(strerrbuf,
 #if defined(NLS)
-			catgets(catd, 1, errnum, sys_errlist[errnum]),
+			catgets(catd, 1, errnum, __hidden_sys_errlist[errnum]),
 #else
-			sys_errlist[errnum],
+			__hidden_sys_errlist[errnum],
 #endif
 			buflen) >= buflen)
 		retval = ERANGE;