[RFC PATCH v1 2/7] samples/landlock: Clarify option parsing behaviour

[Mickaël Salaün]

On Mon, Sep 16, 2024 at 02:22:25PM +0200, Matthieu Buffet wrote:
> - Clarify which environment variables are optional, which ones are
>   mandatory
> - Clarify the difference between unset variables and empty ones
> - Move the (larger) help message to a helper function
> 
> Signed-off-by: Matthieu Buffet <matthieu at buffet.re>
> ---
>  samples/landlock/sandboxer.c | 86 ++++++++++++++++++++----------------
>  1 file changed, 48 insertions(+), 38 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index a84ae3a15482..08704504dc51 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -221,6 +221,53 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>  
>  #define LANDLOCK_ABI_LAST 5
>  
> +static void print_help(const char *prog)
> +{
> +	fprintf(stderr,
> +		"usage: %s=\"...\" %s=\"...\" [other environment variables] %s "
> +		"<cmd> [args]...\n\n",
> +		ENV_FS_RO_NAME, ENV_FS_RW_NAME, prog);
> +	fprintf(stderr,
> +		"Execute a command in a restricted environment.\n\n");
> +	fprintf(stderr,
> +		"Environment variables containing paths and ports "
> +		"can be multi-valued, with a colon delimiter.\n"
> +		"\n"
> +		"Mandatory settings:\n");
> +	fprintf(stderr,
> +		"* %s: list of paths allowed to be used in a read-only way.\n",
> +		ENV_FS_RO_NAME);
> +	fprintf(stderr,
> +		"* %s: list of paths allowed to be used in a read-write way.\n",
> +		ENV_FS_RW_NAME);
> +	fprintf(stderr,
> +		"\n"
> +		"Optional settings (when not set, their associated access "
> +		"check is always allowed) (for lists, an empty string means "
> +		"to allow nothing, e.g. %s=\"\"):\n",
> +		ENV_TCP_BIND_NAME);
> +	fprintf(stderr,
> +		"* %s: list of ports allowed to bind (server).\n",
> +		ENV_TCP_BIND_NAME);
> +	fprintf(stderr,
> +		"* %s: list of ports allowed to connect (client).\n",
> +		ENV_TCP_CONNECT_NAME);
> +	fprintf(stderr,
> +		"\n"
> +		"Example:\n"
> +		"%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
> +		"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
> +		"%s=\"9418\" "
> +		"%s=\"80:443\" "
> +		"%s bash -i\n\n",
> +		ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
> +		ENV_TCP_CONNECT_NAME, prog);
> +	fprintf(stderr,
> +		"This sandboxer can use Landlock features "
> +		"up to ABI version %d.\n",
> +		LANDLOCK_ABI_LAST);
> +}
> +
>  int main(const int argc, char *const argv[], char *const *const envp)
>  {
>  	const char *cmd_path;
> @@ -237,44 +284,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  	};
>  
>  	if (argc < 2) {
> -		fprintf(stderr,
> -			"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
> -			"<cmd> [args]...\n\n",
> -			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
> -			ENV_TCP_CONNECT_NAME, argv[0]);
> -		fprintf(stderr,
> -			"Execute a command in a restricted environment.\n\n");
> -		fprintf(stderr,
> -			"Environment variables containing paths and ports "
> -			"each separated by a colon:\n");
> -		fprintf(stderr,
> -			"* %s: list of paths allowed to be used in a read-only way.\n",
> -			ENV_FS_RO_NAME);
> -		fprintf(stderr,
> -			"* %s: list of paths allowed to be used in a read-write way.\n\n",
> -			ENV_FS_RW_NAME);
> -		fprintf(stderr,
> -			"Environment variables containing ports are optional "
> -			"and could be skipped.\n");
> -		fprintf(stderr,
> -			"* %s: list of ports allowed to bind (server).\n",
> -			ENV_TCP_BIND_NAME);
> -		fprintf(stderr,
> -			"* %s: list of ports allowed to connect (client).\n",
> -			ENV_TCP_CONNECT_NAME);
> -		fprintf(stderr,
> -			"\nexample:\n"
> -			"%s=\"${PATH}:/lib:/usr:/proc:/etc:/dev/urandom\" "
> -			"%s=\"/dev/null:/dev/full:/dev/zero:/dev/pts:/tmp\" "
> -			"%s=\"9418\" "
> -			"%s=\"80:443\" "
> -			"%s bash -i\n\n",
> -			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
> -			ENV_TCP_CONNECT_NAME, argv[0]);
> -		fprintf(stderr,
> -			"This sandboxer can use Landlock features "
> -			"up to ABI version %d.\n",
> -			LANDLOCK_ABI_LAST);
> +		print_help(argv[0]);

Looks good, please rebase on my "next" branch with the new LL_SCOPED
variable and send it in a new series along with the previous fix:
https://git.kernel.org/pub/scm/linux/kernel/git/mic/linux.git/log/?h=next

>  		return 1;
>  	}
>  
> -- 
> 2.39.5
> 
>