su: add a basic implementation for WIN32

Use the undocumented 'runas' verb in a call to ShellExecuteEx()
to run a shell with elevated privileges.

Because of the way ShellExecuteEx() works this:

- requires that you acknowledge a User Account Control prompt (if
  you're an Administrator);
- requires that you enter an Administrator's password (if you aren't
  an Administrator);
- creates a separate console window for the privileged shell.

Variables from the parent shell aren't passed to its privileged child,
only variables from the environment.

It's possible to specify a command to run when the shell starts.
This can be used to pass shell variables:

  su -c "HELLO='hello world'; GOODBYE=$GOODBYE"

Or do fancy things like:

  su -c "ls -l; read -p 'Hit return to exit: '; exit"

It's probably best to put double quotes around the command and use
single quotes inside it.  Apparently ShellExecuteEx() requires
double quotes to be entered in triplicate:

  su -c 'HELLO="""hello world"""'

2 files changed, 51 insertions, 0 deletions

diff --git a/loginutils/su.c b/loginutils/su.c
index 41291ea8f..2e1b309b0 100644
--- a/loginutils/su.c
+++ b/loginutils/su.c
@@ -8,6 +8,7 @@
 //config:       bool "su (19 kb)"
 //config:       default y
 //config:       select FEATURE_SYSLOG
+//config:       depends on PLATFORM_POSIX
 //config:       help
 //config:       su is used to become another user during a login session.
 //config:       Invoked without a username, su defaults to becoming the super user.
diff --git a/loginutils/suw32.c b/loginutils/suw32.c
new file mode 100644
index 000000000..3aa478f33
--- /dev/null
+++ b/loginutils/suw32.c
@@ -0,0 +1,50 @@
+/* vi: set sw=4 ts=4: */
+/*
+ * Mini su implementation for busybox-w32
+ *
+ * Licensed under GPLv2 or later, see file LICENSE in this source tree.
+ */
+//config:config SUW32
+//config:       bool "su for Microsoft Windows"
+//config:       default y
+//config:       depends on PLATFORM_MINGW32 && ASH
+//config:       help
+//config:       su runs a shell with elevated privileges.
+
+//applet:IF_SUW32(APPLET_ODDNAME(su, suw32, BB_DIR_BIN, BB_SUID_DROP, suw32))
+
+//kbuild:lib-$(CONFIG_SUW32) += suw32.o
+
+//usage:#define suw32_trivial_usage
+//usage:       "[-c \"CMD\"]"
+//usage:#define suw32_full_usage "\n\n"
+//usage:       "Run shell with elevated privileges\n"
+//usage:     "\n    -c CMD  Command to pass to 'sh -c'"
+
+#include "libbb.h"
+
+int suw32_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
+int suw32_main(int argc UNUSED_PARAM, char **argv)
+{
+        char *opt_command = NULL;
+        SHELLEXECUTEINFO info;
+
+        getopt32(argv, "c:", &opt_command);
+        if (argv[optind])
+                bb_show_usage();
+
+        memset(&info, 0, sizeof(SHELLEXECUTEINFO));
+        info.cbSize = sizeof(SHELLEXECUTEINFO);
+        /* info.fMask = SEE_MASK_DEFAULT; */
+        /* info.hwnd = NULL; */
+        info.lpVerb = "runas";
+        info.lpFile = bb_busybox_exec_path;
+        if (opt_command)
+                info.lpParameters = xasprintf("ash -s -c \"%s\"", opt_command);
+        else
+                info.lpParameters = "ash";
+        /* info.lpDirectory = NULL; */
+        info.nShow = SW_SHOWNORMAL;
+
+        return !ShellExecuteEx(&info);
+}