su: add test mode

Testing some uses of 'su' can be challenging because any errors
appear in the new console window which may close as a result.

Add the '-t' option to enable test mode.  This starts a new shell
using ShellExecuteEx(), but without elevated privileges and a new
console.  All other options and arguments are handled much as
before, though some differences in behaviour are to be expected due
to the lack of elevated privilege.

Adds 80-96 bytes.

(GitHub issue #438)

1 files changed, 27 insertions, 19 deletions

diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index 821071388..11935e326 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -16,14 +16,15 @@
 //kbuild:lib-$(CONFIG_SUW32) += suw32.o
 
 //usage:#define suw32_trivial_usage
-//usage:       "[-W] [-N|-s SHELL] [root]\n"
-//usage:       "or:    su [-W] [-N|-s SHELL] -c CMD_STRING [[--] root [ARG0 [ARG...]]]\n"
-//usage:       "or:    su [-W] [-N|-s SHELL] [--] root [arbitrary sh arguments]"
+//usage:       "[-tW] [-N|-s SHELL] [root]\n"
+//usage:       "or:    su [-tW] [-N|-s SHELL] -c CMD_STRING [[--] root [ARG0 [ARG...]]]\n"
+//usage:       "or:    su [-tW] [-N|-s SHELL] [--] root [arbitrary sh arguments]"
 //usage:#define suw32_full_usage "\n\n"
 //usage:       "Run shell with elevated privileges\n"
 //usage:     "\n    -c CMD    Command to pass to 'sh -c'"
 //usage:     "\n    -s SHELL  Use specified shell"
 //usage:     "\n    -N        Don't close console when shell exits"
+//usage:     "\n    -t        Test mode, no elevation"
 //usage:     "\n    -W        Wait for shell exit code"
 
 #include "libbb.h"
@@ -32,10 +33,13 @@
 enum {
         OPT_c = (1 << 0),
         OPT_s = (1 << 1),
-        OPT_N = (1 << 2),
-        OPT_W = (1 << 3)
+        OPT_t = (1 << 2),
+        OPT_N = (1 << 3),
+        OPT_W = (1 << 4)
 };
 
+#define test_mode (opt & OPT_t)
+
 int suw32_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int suw32_main(int argc UNUSED_PARAM, char **argv)
 {
@@ -47,25 +51,25 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         char *bb_path, *cwd, *realcwd, *q, *args;
         DECLARE_PROC_ADDR(BOOL, ShellExecuteExA, SHELLEXECUTEINFOA *);
 
+        opt = getopt32(argv, "^c:s:tNW" "\0" "s--N:N--s", &opt_command, &opt_shell);
+        argv += optind;
+        if (argv[0]) {
+                if (!test_mode && strcmp(argv[0], "root") != 0) {
+                        bb_error_msg_and_die("unknown user '%s'", argv[0]);
+                }
+                ++argv;
+        }
+
 #if ENABLE_DROP || ENABLE_CDROP || ENABLE_PDROP
         // If privilege has been dropped (ELEVATED_PRIVILEGE but not
         // ADMIN_ENABLED) ShellExecuteEx() thinks we already have elevated
         // privilege and doesn't raise privilege.  In that case, give up.
-        if (elevation_state() == ELEVATED_PRIVILEGE) {
+        if (!test_mode && elevation_state() == ELEVATED_PRIVILEGE) {
                 xfunc_error_retval = 2;
                 bb_error_msg_and_die("unable to restore privilege");
         }
 #endif
 
-        opt = getopt32(argv, "^c:s:NW" "\0" "s--N:N--s", &opt_command, &opt_shell);
-        argv += optind;
-        if (argv[0]) {
-                if (strcmp(argv[0], "root") != 0) {
-                        bb_error_msg_and_die("unknown user '%s'", argv[0]);
-                }
-                ++argv;
-        }
-
         /* ShellExecuteEx() needs backslash as separator in UNC paths. */
         if (opt_shell) {
                 bb_path = file_is_win32_exe(opt_shell);
@@ -74,17 +78,21 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
                 args = NULL;
         } else {
                 bb_path = xstrdup(bb_busybox_exec_path);
-                args = xasprintf("--busybox ash -t \"BusyBox ash (Admin)\"");
+                args = xstrdup("--busybox ash");
+                if (!test_mode)
+                        args = xappendword(args, "-t \"BusyBox ash (Admin)\"");
         }
         slash_to_bs(bb_path);
 
         memset(&info, 0, sizeof(SHELLEXECUTEINFO));
         info.cbSize = sizeof(SHELLEXECUTEINFO);
         /* info.fMask = SEE_MASK_DEFAULT; */
-        if (opt & OPT_W)
+        if (opt & (OPT_t|OPT_W))
                 info.fMask |= SEE_MASK_NOCLOSEPROCESS;
+        if (test_mode)
+                info.fMask |= SEE_MASK_NO_CONSOLE;
         /* info.hwnd = NULL; */
-        info.lpVerb = "runas";
+        info.lpVerb = !test_mode ? "runas" : "open";
         info.lpFile = bb_path;
         /*
          * It seems that when ShellExecuteEx() runs binaries residing in
@@ -139,7 +147,7 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
                 goto end;
         }
 
-        if (opt & OPT_W) {
+        if (opt & (OPT_t|OPT_W)) {
                 DWORD r;
 
                 WaitForSingleObject(info.hProcess, INFINITE);