su: allow an alternative shell to be selected

Add the '-s' option to allow an alternative shell to be given.
No PATH search is performed for the shell, so an absolute or
relative path to a suitable executable must be provided.

Certain features are only available when the built-in shell is
used:

- The '-N' option, which allows the console window to remain open
  when the shell exits.

- The fix which allows the current directory to be retained despite
  the efforts of ShellExecute() to change it.

- The friendly message in the console title.

Adds 128 bytes.

(GitHub issue #438)

1 files changed, 30 insertions, 19 deletions

diff --git a/loginutils/suw32.c b/loginutils/suw32.c
index a0afe5bb7..cbe727969 100644
--- a/loginutils/suw32.c
+++ b/loginutils/suw32.c
@@ -16,22 +16,24 @@
 //kbuild:lib-$(CONFIG_SUW32) += suw32.o
 
 //usage:#define suw32_trivial_usage
-//usage:       "[-NW] [root]\n"
-//usage:       "or:    su [-NW] -c CMD_STRING [[--] root [ARG0 [ARG...]]]\n"
-//usage:       "or:    su [-NW] [--] root [arbitrary sh arguments]"
+//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:#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    -N      Don't close console when shell exits"
-//usage:     "\n    -W      Wait for shell exit code"
+//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    -W        Wait for shell exit code"
 
 #include "libbb.h"
 #include "lazyload.h"
 
 enum {
         OPT_c = (1 << 0),
-        OPT_N = (1 << 1),
-        OPT_W = (1 << 2)
+        OPT_s = (1 << 1),
+        OPT_N = (1 << 2),
+        OPT_W = (1 << 3)
 };
 
 int suw32_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
@@ -40,6 +42,7 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         int ret = 0;
         unsigned opt;
         char *opt_command = NULL;
+        char *opt_shell = NULL;
         SHELLEXECUTEINFO info;
         char *bb_path, *cwd, *realcwd, *q, *args;
         DECLARE_PROC_ADDR(BOOL, ShellExecuteExA, SHELLEXECUTEINFOA *);
@@ -54,7 +57,7 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         }
 #endif
 
-        opt = getopt32(argv, "c:NW", &opt_command);
+        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) {
@@ -64,7 +67,15 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
         }
 
         /* ShellExecuteEx() needs backslash as separator in UNC paths. */
-        bb_path = xstrdup(bb_busybox_exec_path);
+        if (opt_shell) {
+                bb_path = file_is_win32_exe(opt_shell);
+                if (!bb_path)
+                        bb_error_msg_and_die("%s: Not found", opt_shell);
+                args = NULL;
+        } else {
+                bb_path = xstrdup(bb_busybox_exec_path);
+                args = xasprintf("--busybox ash -t \"BusyBox ash (Admin)\"");
+        }
         slash_to_bs(bb_path);
 
         memset(&info, 0, sizeof(SHELLEXECUTEINFO));
@@ -85,15 +96,15 @@ int suw32_main(int argc UNUSED_PARAM, char **argv)
          * a network share it may not be available once we have elevated
          * privileges.
          */
-        args = xasprintf("--busybox ash -t \"BusyBox ash (Admin)\"");
-
-        cwd = getcwd(NULL, 0);
-        realcwd = cwd ? xmalloc_realpath(cwd) : NULL;
-        if (realcwd || cwd) {
-                args = xappendword(args, "-d");
-                q = quote_arg(realcwd ?: cwd);
-                args = xappendword(args, q);
-                free(q);
+        if (opt_shell == NULL) {
+                cwd = getcwd(NULL, 0);
+                realcwd = cwd ? xmalloc_realpath(cwd) : NULL;
+                if (realcwd || cwd) {
+                        args = xappendword(args, "-d");
+                        q = quote_arg(realcwd ?: cwd);
+                        args = xappendword(args, q);
+                        free(q);
+                }
         }
 
         if (opt & OPT_N)