runuser,drop: drop runuser, tweak drop

Remove the runuser applet, leaving only drop.  Move drop from
util-linux to miscutils.

A command of the form 'drop -c command' causes the BusyBox shell
to be used, just like 'drop' without any arguments.  A simple
OpenSSH configuration with 'drop.exe' as DefaultShell and no
DefaultShellArguments now works both for interactive login and
to run a command.  This is useful for older versions of OpenSSH
which don't support DefaultShellArguments.

Saves 208-232 bytes.

4 files changed, 18 insertions, 52 deletions

diff --git a/configs/mingw32_defconfig b/configs/mingw32_defconfig
index 611fd327a..31f72a450 100644
--- a/configs/mingw32_defconfig
+++ b/configs/mingw32_defconfig
@@ -1,7 +1,7 @@
 #
 # Automatically generated make config: don't edit
 # Busybox version: 1.37.0.git
-# Sun Mar 12 09:41:00 2023
+# Sun Mar 19 09:51:34 2023
 #
 CONFIG_HAVE_DOT_CONFIG=y
 # CONFIG_PLATFORM_POSIX is not set
@@ -707,7 +707,7 @@ CONFIG_XXD=y
 # CONFIG_RENICE is not set
 CONFIG_REV=y
 # CONFIG_RTCWAKE is not set
-CONFIG_RUNUSER=y
+CONFIG_DROP=y
 # CONFIG_SCRIPT is not set
 # CONFIG_SCRIPTREPLAY is not set
 # CONFIG_SETARCH is not set
diff --git a/configs/mingw64_defconfig b/configs/mingw64_defconfig
index 6db0accbf..b5b02ba63 100644
--- a/configs/mingw64_defconfig
+++ b/configs/mingw64_defconfig
@@ -1,7 +1,7 @@
 #
 # Automatically generated make config: don't edit
 # Busybox version: 1.37.0.git
-# Sun Mar 12 09:41:00 2023
+# Sun Mar 19 09:51:34 2023
 #
 CONFIG_HAVE_DOT_CONFIG=y
 # CONFIG_PLATFORM_POSIX is not set
@@ -707,7 +707,7 @@ CONFIG_XXD=y
 # CONFIG_RENICE is not set
 CONFIG_REV=y
 # CONFIG_RTCWAKE is not set
-CONFIG_RUNUSER=y
+CONFIG_DROP=y
 # CONFIG_SCRIPT is not set
 # CONFIG_SCRIPTREPLAY is not set
 # CONFIG_SETARCH is not set
diff --git a/util-linux/runuser.c b/miscutils/drop.c
index 993a4ed68..3e71f6180 100644
--- a/util-linux/runuser.c
+++ b/miscutils/drop.c
@@ -1,20 +1,11 @@
 /* vi: set sw=4 ts=4: */
 /*
- * runuser - run a shell without elevated privileges.
- * This is a much restricted, Windows-specific reimplementation of
- * runuser from util-linux.
+ * drop - run a command without elevated privileges.
  *
  * Copyright (c) 2023 Ronald M Yorston
  *
  * Licensed under GPLv2 or later, see file LICENSE in this source tree.
  */
-//config:config RUNUSER
-//config:       bool "runuser"
-//config:       default y
-//config:       depends on PLATFORM_MINGW32 && SH_IS_ASH
-//config:       help
-//config:       Run a shell without elevated privileges
-//config:
 //config:config DROP
 //config:       bool "drop"
 //config:       default y
@@ -22,39 +13,24 @@
 //config:       help
 //config:       Run a command without elevated privileges
 
-//applet:IF_RUNUSER(APPLET(runuser, BB_DIR_USR_BIN, BB_SUID_DROP))
-//applet:IF_DROP(APPLET_ODDNAME(drop, runuser, BB_DIR_USR_BIN, BB_SUID_DROP, drop))
+//applet:IF_DROP(APPLET(drop, BB_DIR_USR_BIN, BB_SUID_DROP))
 
-//kbuild:lib-$(CONFIG_RUNUSER) += runuser.o
-//kbuild:lib-$(CONFIG_DROP) += runuser.o
-
-//usage:#define runuser_trivial_usage
-//usage:        "USER [ARG...]"
-//usage:#define runuser_full_usage "\n\n"
-//usage:        "Run a shell without elevated privileges. The user name\n"
-//usage:        "must be that of the user who was granted those privileges.\n"
-//usage:        "Any arguments are passed to the shell.\n"
+//kbuild:lib-$(CONFIG_DROP) += drop.o
 
 //usage:#define drop_trivial_usage
-//usage:        "[COMMAND [ARG...]]"
+//usage:        "[COMMAND | -c [ARG...]]"
 //usage:#define drop_full_usage "\n\n"
-//usage:        "Run a command without elevated privileges. Run the BusyBox\n"
-//usage:        "shell if no COMMAND is provided. Any arguments are passed\n"
-//usage:        "to the command.\n"
+//usage:        "Drop elevated privileges and run a command. If no COMMAND\n"
+//usage:        "is provided run the BusyBox shell.\n"
 
 #include "libbb.h"
 #include <winsafer.h>
 #include <lazyload.h>
 
-int runuser_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int runuser_main(int argc, char **argv)
+int drop_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int drop_main(int argc, char **argv)
 {
-#if ENABLE_RUNUSER && ENABLE_DROP
-        int is_runuser = strcmp(applet_name, "runuser") == 0;
-#else
-        const int is_runuser = ENABLE_RUNUSER;
-#endif
-        const char *user, *exe;
+        const char *exe;
         SAFER_LEVEL_HANDLE safer;
         HANDLE token;
         STARTUPINFO si;
@@ -77,18 +53,6 @@ int runuser_main(int argc, char **argv)
         if (!INIT_PROC_ADDR(advapi32.dll, CreateProcessAsUserA))
                 bb_simple_error_msg_and_die("not supported");
 
-        if (is_runuser) {
-                if (getuid() != 0)
-                        bb_simple_error_msg_and_die("may not be used by non-root users");
-
-                if (argc < 2)
-                        bb_show_usage();
-
-                user = get_user_name();
-                if (user == NULL || strcmp(argv[1], user) != 0)
-                        bb_simple_error_msg_and_die("invalid user");
-        }
-
         /*
          * Run a shell using a token with reduced privilege.  Hints from:
          *
@@ -103,10 +67,12 @@ int runuser_main(int argc, char **argv)
                 TIL.Label.Attributes = SE_GROUP_INTEGRITY;
                 if (SetTokenInformation(token, TokenIntegrityLevel, &TIL,
                                                 sizeof(TOKEN_MANDATORY_LABEL))) {
+                        int skip = 1;
 
-                        if (is_runuser || argc == 1) {
+                        if (argc == 1 || strcmp(argv[1], "-c") == 0) {
                                 exe = bb_busybox_exec_path;
                                 cmd = xstrdup("sh");
+                                skip = 0;
                         } else {
                                 char *file;
 
@@ -132,7 +98,7 @@ int runuser_main(int argc, char **argv)
                         }
 
                         // Build the command line
-                        for (a = argv + 1 + (argc != 1); *a; ++a) {
+                        for (a = argv + 1 + skip; *a; ++a) {
                                 q = quote_arg(*a);
                                 newcmd = xasprintf("%s %s", cmd, q);
                                 free(q);
diff --git a/win32/mingw.c b/win32/mingw.c
index fd670ebf6..1fdb8cad9 100644
--- a/win32/mingw.c
+++ b/win32/mingw.c
@@ -1136,7 +1136,7 @@ char *get_user_name(void)
         return user_name;
 }
 
-#if ENABLE_RUNUSER || ENABLE_DROP
+#if ENABLE_DROP
 /*
  * When runuser drops privileges TokenIsElevated still returns TRUE.
  * Use other means to determine if we're actually unprivileged.