[PATCH v3] setpriv: new applet

[Assaf Gordon]

Add a minimal 'setpriv' implementation supporting the NO_NEW_PRIVS bit.
As upstream only supports long options (--nnp/--no-new-privs),
A non-standard "-N" option is also added for the applet.

Typical usage:

    $ busybox setpriv sudo uname
    Linux
    $ busybox setpriv --nnp sudo uname
    sudo: effective uid is not 0, is /usr/bin/sudo on a file system with
    the 'nosuid' option set or an NFS file system without root privileges?

Signed-off-by: Assaf Gordon <assafgordon at gmail.com>
---
 util-linux/setpriv.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)
 create mode 100644 util-linux/setpriv.c

diff --git a/util-linux/setpriv.c b/util-linux/setpriv.c
new file mode 100644
index 0000000..f8e4170
--- /dev/null
+++ b/util-linux/setpriv.c
@@ -0,0 +1,73 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * setpriv implementation for busybox based on linux-utils-ng 2.29
+ *
+ * Copyright (C) 2017 by  <assafgordon at gmail.com>
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ *
+ */
+//config:config SETPRIV
+//config:	bool "setpriv"
+//config:	default y
+//config:	select PLATFORM_LINUX
+//config:	help
+//config:	  run a program with different Linux privilege settings
+//config:	  currently only --no-new-privs is supported
+//config:	  Requires kernel >= 3.5
+//config:
+//config:config FEATURE_SETPRIV_LONG_OPTS
+//config:	bool "Enable long options"
+//config:	default y
+//config:	depends on SETPRIV && LONG_OPTS
+//config:	help
+//config:	  Support long options for the setpriv applet. This makes
+//config:	  the busybox implementation more compatible with upstream.
+
+//applet:IF_SETPRIV(APPLET(setpriv, BB_DIR_BIN, BB_SUID_DROP))
+
+//kbuild:lib-$(CONFIG_SETPRIV) += setpriv.o
+
+//usage:#define setpriv_trivial_usage
+//usage:	"[OPTIONS] PROG [ARGS]"
+//usage:#if ENABLE_FEATURE_SETPRIV_LONG_OPTS
+//usage:#define setpriv_full_usage "\n\n"
+//usage:       "run a program with different Linux privilege settings\n"
+//usage:     "\n-N,--nnp,--no-new-privs	 Set the no_new_privs bit\n"
+//usage:#else
+//usage:#define setpriv_full_usage "\n\n"
+//usage:       "run a program with different Linux privilege settings\n"
+//usage:     "\n-N	 Set the no_new_privs bit\n"
+//usage:#endif
+
+#include <sys/syscall.h>
+#include <sys/prctl.h>
+#include <asm/unistd.h>
+#include "libbb.h"
+
+/*
+ * Upstream setpriv doesn't support the short option for --nnp/--no-new-privs.
+ * Invent new short-option 'N'
+ */
+static const char opt_str[] ALIGN1 = "N";
+
+#if ENABLE_FEATURE_SETPRIV_LONG_OPTS
+static const char setpriv_longopts[] ALIGN1 =
+	"nnp\0"				No_argument	"N"
+	"no-new-privs\0"	No_argument	"N"
+;
+#endif
+
+int setpriv_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int setpriv_main(int argc UNUSED_PARAM, char **argv)
+{
+	opt_complementary = "-1";
+
+	IF_FEATURE_SETPRIV_LONG_OPTS(applet_long_options = setpriv_longopts);
+	if (getopt32(argv, opt_str))
+		if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0))
+			bb_simple_perror_msg_and_die("prctl: NO_NEW_PRIVS");
+
+	argv += optind;
+	BB_EXECVP_or_die(argv);
+}
-- 
2.1.4