[PATCH] libbb: '--help' handling in standalone shell mode

[Denys Vlasenko]

Thank you for finding this bug.
I committed a somewhat different fix, one which
factors out the code to detect --help
(some applets opt out of handling it specially).

On Thu, Feb 18, 2021 at 8:44 AM Ron Yorston <rmy at pobox.com> wrote:
>
> Most BusyBox applets respond to the '--help' option by printing
> a usage message.  This is normally handled by busybox_main() so
> applet main routines don't have support for '--help'.
>
> In standalone shell mode with FEATURE_SH_NOFORK enabled nofork
> applets are invoked directly, bypassing busybox_main().  This
> results in inconsistent handling of '--help':
>
> - applets which call getopt() report "unrecognized option '--help'"
>   and print help anyway;
>
> - realpath says "--help: No such file or directory" and doesn't
>   print help;
>
> - usleep says "invalid number '--help'" and doesn't print help.
>
> Avoid inconsistency by checking for '--help' in run_nofork_applet().
>
> Signed-off-by: Ron Yorston <rmy at pobox.com>
> ---
>  libbb/vfork_daemon_rexec.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/libbb/vfork_daemon_rexec.c b/libbb/vfork_daemon_rexec.c
> index 65271e84f..a9ce280dd 100644
> --- a/libbb/vfork_daemon_rexec.c
> +++ b/libbb/vfork_daemon_rexec.c
> @@ -109,6 +109,8 @@ int FAST_FUNC run_nofork_applet(int applet_no, char **argv)
>                 char *tmp_argv[argc+1];
>                 memcpy(tmp_argv, argv, (argc+1) * sizeof(tmp_argv[0]));
>                 applet_name = tmp_argv[0];
> +               if (argc == 2 && strcmp(argv[1], "--help") == 0)
> +                       bb_show_usage();
>                 /* Finally we can call NOFORK applet's main() */
>                 rc = applet_main[applet_no](argc, tmp_argv);
>                 /* Important for shells: `which CMD` was failing */
> --
> 2.29.2
>
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