drop: 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.

Adds 80-96 bytes.

(GitHub issue #438)

1 files changed, 16 insertions, 7 deletions

diff --git a/miscutils/drop.c b/miscutils/drop.c
index 629460564..a1344ab65 100644
--- a/miscutils/drop.c
+++ b/miscutils/drop.c
@@ -36,10 +36,10 @@
 //kbuild:lib-$(CONFIG_PDROP) += drop.o
 
 //usage:#define drop_trivial_usage
-//usage:        "[COMMAND [ARG...] | -c CMD_STRING [ARG...]]"
+//usage:        "[COMMAND [ARG...] | [-s SHELL] -c CMD_STRING [ARG...]]"
 //usage:#define drop_full_usage "\n\n"
 //usage:        "Drop elevated privileges and run a command. If no command\n"
-//usage:        "is provided run the BusyBox shell.\n"
+//usage:        "is provided run a shell (by default, the BusyBox shell).\n"
 
 //usage:#define cdrop_trivial_usage
 //usage:        "[COMMAND [ARG...] | -c CMD_STRING [ARG...]]"
@@ -71,7 +71,7 @@ static void setenv_name(const char *key)
 }
 
 int drop_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
-int drop_main(int argc, char **argv)
+int drop_main(int argc UNUSED_PARAM, char **argv)
 {
         SAFER_LEVEL_HANDLE safer;
         HANDLE token;
@@ -109,15 +109,19 @@ int drop_main(int argc, char **argv)
                 if (SetTokenInformation(token, TokenIntegrityLevel, &TIL,
                                                 sizeof(TOKEN_MANDATORY_LABEL))) {
                         char *opt_command = NULL;
+                        char *opt_shell = NULL;
                         char **a;
                         const char *opt, *arg;
                         char *exe, *cmd, *q;
 
-                        getopt32(argv, "c:", &opt_command);
+                        if (*applet_name == 'd')
+                                getopt32(argv, "c:s:", &opt_command, &opt_shell);
+                        else
+                                getopt32(argv, "c:", &opt_command);
                         a = argv + optind;
                         opt = "-c";
 
-                        if (argc == 1 || opt_command) {
+                        if (*a == NULL || opt_command) {
                                 switch (*applet_name) {
 #if ENABLE_PDROP
                                 case 'p':
@@ -134,8 +138,13 @@ int drop_main(int argc, char **argv)
 #endif
 #if ENABLE_DROP
                                 case 'd':
-                                        arg = "sh";
-                                        exe = xstrdup(bb_busybox_exec_path);
+                                        if (opt_shell) {
+                                                arg = bb_basename(opt_shell);
+                                                exe = file_is_win32_exe(opt_shell);
+                                        } else {
+                                                arg = "sh";
+                                                exe = xstrdup(bb_busybox_exec_path);
+                                        }
                                         break;
 #endif
                                 default: