su: expand help; simplify passing of -c CMD to run_shell()

Also, added a comment about bug 9401 (TIOCSTI input injection).

function                                             old     new   delta
packed_usage                                       30909   30932     +23
su_main                                              470     487     +17
sulogin_main                                         260     258      -2
run_applet_and_exit                                  681     678      -3
run_shell                                            166     126     -40

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

2 files changed, 13 insertions, 18 deletions

diff --git a/libbb/executable.c b/libbb/executable.c
index 05e70312f..3a1d4ff44 100644
--- a/libbb/executable.c
+++ b/libbb/executable.c
@@ -97,5 +97,5 @@ void FAST_FUNC exec_prog_or_SHELL(char **argv)
         if (argv[0]) {
                 BB_EXECVP_or_die(argv);
         }
-        run_shell(getenv("SHELL"), /*login:*/ 1, NULL, NULL);
+        run_shell(getenv("SHELL"), /*login:*/ 1, NULL);
 }
diff --git a/libbb/run_shell.c b/libbb/run_shell.c
index 4d92c3caa..b6b9360e8 100644
--- a/libbb/run_shell.c
+++ b/libbb/run_shell.c
@@ -50,19 +50,17 @@ void FAST_FUNC set_current_security_context(security_context_t sid)
 #endif
 
 /* Run SHELL, or DEFAULT_SHELL if SHELL is "" or NULL.
- * If COMMAND is nonzero, pass it to the shell with the -c option.
- * If ADDITIONAL_ARGS is nonzero, pass it to the shell as more
- * arguments.  */
-void FAST_FUNC run_shell(const char *shell, int loginshell, const char *command, const char **additional_args)
+ * If ADDITIONAL_ARGS is not NULL, pass them to the shell.
+ */
+void FAST_FUNC run_shell(const char *shell, int loginshell, const char **additional_args)
 {
         const char **args;
-        int argno;
-        int additional_args_cnt = 0;
 
-        for (args = additional_args; args && *args; args++)
-                additional_args_cnt++;
+        args = additional_args;
+        while (args && *args)
+                args++;
 
-        args = xmalloc(sizeof(char*) * (4 + additional_args_cnt));
+        args = xmalloc(sizeof(char*) * (2 + (args - additional_args)));
 
         if (!shell || !shell[0])
                 shell = DEFAULT_SHELL;
@@ -70,16 +68,13 @@ void FAST_FUNC run_shell(const char *shell, int loginshell, const char *command,
         args[0] = bb_get_last_path_component_nostrip(shell);
         if (loginshell)
                 args[0] = xasprintf("-%s", args[0]);
-        argno = 1;
-        if (command) {
-                args[argno++] = "-c";
-                args[argno++] = command;
-        }
+        args[1] = NULL;
         if (additional_args) {
-                for (; *additional_args; ++additional_args)
-                        args[argno++] = *additional_args;
+                int cnt = 1;
+                for (;;)
+                        if ((args[cnt++] = *additional_args++) == NULL)
+                                break;
         }
-        args[argno] = NULL;
 
 #if ENABLE_SELINUX
         if (current_sid)