Index: include/unistd.h
===================================================================
--- include/unistd.h	(revision 228798)
+++ include/unistd.h	(working copy)
@@ -494,6 +494,7 @@
 int	 iruserok(unsigned long, int, const char *, const char *);
 int	 iruserok_sa(const void *, int, int, const char *, const char *);
 int	 issetugid(void);
+void	__FreeBSD_libc_enter_restricted_mode(void);
 char	*mkdtemp(char *);
 #ifndef	_MKNOD_DECLARED
 int	 mknod(const char *, mode_t, dev_t);
Index: lib/libc/include/libc_private.h
===================================================================
--- lib/libc/include/libc_private.h	(revision 228798)
+++ lib/libc/include/libc_private.h	(working copy)
@@ -44,6 +44,17 @@
 extern int	__isthreaded;
 
 /*
+ * libc should use libc_dlopen internally, which respects a global
+ * flag where loading of new shared objects can be restricted.
+ */
+void *libc_dlopen(const char *, int);
+
+/*
+ * For dynamic linker.
+ */
+void _rtld_error(const char *fmt, ...);
+
+/*
  * File lock contention is difficult to diagnose without knowing
  * where locks were set. Allow a debug library to be built which
  * records the source file and line number of each lock call.
Index: lib/libc/Versions.def
===================================================================
--- lib/libc/Versions.def	(revision 228798)
+++ lib/libc/Versions.def	(working copy)
@@ -20,9 +20,13 @@
 FBSD_1.2 {
 } FBSD_1.1;
 
+# This version was first added to 10.0-current.
+FBSD_1.3 {
+} FBSD_1.2;
+
 # This is our private namespace.  Any global interfaces that are
 # strictly for use only by other FreeBSD applications and libraries
 # are listed here.  We use a separate namespace so we can write
 # simple ABI-checking tools.
 FBSDprivate_1.0 {
-} FBSD_1.2;
+} FBSD_1.3;
Index: lib/libc/net/nsdispatch.c
===================================================================
--- lib/libc/net/nsdispatch.c	(revision 228798)
+++ lib/libc/net/nsdispatch.c	(working copy)
@@ -369,7 +369,7 @@
 	confmod = statbuf.st_mtime;
 
 #ifdef NS_CACHING
-	handle = dlopen(NULL, RTLD_LAZY | RTLD_GLOBAL);
+	handle = libc_dlopen(NULL, RTLD_LAZY | RTLD_GLOBAL);
 	if (handle != NULL) {
 		nss_cache_cycle_prevention_func = dlsym(handle,
 			"_nss_cache_cycle_prevention_function");
@@ -482,7 +482,7 @@
 		if (snprintf(buf, sizeof(buf), "nss_%s.so.%d", mod.name,
 		    NSS_MODULE_INTERFACE_VERSION) >= (int)sizeof(buf))
 			goto fin;
-		mod.handle = dlopen(buf, RTLD_LOCAL|RTLD_LAZY);
+		mod.handle = libc_dlopen(buf, RTLD_LOCAL|RTLD_LAZY);
 		if (mod.handle == NULL) {
 #ifdef _NSS_DEBUG
 			/* This gets pretty annoying since the built-in
Index: lib/libc/gen/Symbol.map
===================================================================
--- lib/libc/gen/Symbol.map	(revision 228798)
+++ lib/libc/gen/Symbol.map	(working copy)
@@ -345,6 +345,10 @@
 	getpagesizes;
 };
 
+FBSD_1.3 {
+	__FreeBSD_libc_enter_restricted_mode;
+};
+
 FBSDprivate_1.0 {
 	/* needed by thread libraries */
 	__thr_jtable;
Index: lib/libc/gen/Makefile.inc
===================================================================
--- lib/libc/gen/Makefile.inc	(revision 228798)
+++ lib/libc/gen/Makefile.inc	(working copy)
@@ -20,6 +20,7 @@
 	getpeereid.c getprogname.c getpwent.c getttyent.c \
 	getusershell.c getvfsbyname.c glob.c \
 	initgroups.c isatty.c isinf.c isnan.c jrand48.c lcong48.c \
+	libc_dlopen.c \
 	lockf.c lrand48.c mrand48.c nftw.c nice.c \
 	nlist.c nrand48.c opendir.c \
 	pause.c pmadvise.c popen.c posixshm.c pselect.c \
Index: lib/libc/gen/libc_dlopen.c
===================================================================
--- lib/libc/gen/libc_dlopen.c	(revision 0)
+++ lib/libc/gen/libc_dlopen.c	(working copy)
@@ -0,0 +1,61 @@
+/*-
+ * Copyright (c) 2011 Xin Li <delphij@FreeBSD.org>
+ * 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.
+ *
+ * $FreeBSD$
+ */
+
+#include <sys/cdefs.h>
+__FBSDID("$FreeBSD$");
+
+#include <dlfcn.h>
+#include <stddef.h>
+#include <unistd.h>
+
+#include "libc_private.h"
+
+/*
+ * Whether we want to restrict dlopen()s.
+ */
+static int __libc_restricted_mode = 0;
+
+void *
+libc_dlopen(const char *path, int mode)
+{
+
+	if (__libc_restricted_mode) {
+		_rtld_error("Service unavailable -- libc in restricted mode");
+		return (NULL);
+	} else
+		return (dlopen(path, mode));
+}
+
+void
+__FreeBSD_libc_enter_restricted_mode(void)
+{
+
+	__libc_restricted_mode = 1;
+	return;
+}
+
Index: libexec/ftpd/popen.c
===================================================================
--- libexec/ftpd/popen.c	(revision 228798)
+++ libexec/ftpd/popen.c	(working copy)
@@ -143,6 +143,9 @@
 			}
 			(void)close(pdes[1]);
 		}
+		/* Drop privileges before proceeding */
+		if (getuid() != geteuid() && setuid(geteuid()) < 0)
+			_exit(1);
 		if (strcmp(gargv[0], _PATH_LS) == 0) {
 			/* Reset getopt for ls_main() */
 			optreset = optind = optopt = 1;
Index: libexec/ftpd/ftpd.c
===================================================================
--- libexec/ftpd/ftpd.c	(revision 228798)
+++ libexec/ftpd/ftpd.c	(working copy)
@@ -1546,6 +1546,7 @@
 			reply(550, "Can't change root.");
 			goto bad;
 		}
+		__FreeBSD_libc_enter_restricted_mode();
 	} else	/* real user w/o chroot */
 		homedir = pw->pw_dir;
 	/*
