Subject: Re: [RFC PATCH v2 9/9] samples/landlock: Support LANDLOCK_ACCESS_NET_LISTEN

From: Günther Noack <[email-masked]>
Date: Sat, 5 Oct 2024 18:57:24 +0200

On Wed, Aug 14, 2024 at 11:01:51AM +0800, Mikhail Ivanov wrote:
> Extend sample with TCP listen control logic.
> 
> Signed-off-by: Mikhail Ivanov <[email-masked]>
> ---
>  samples/landlock/sandboxer.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index e8223c3e781a..3f50cb3f8039 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -55,6 +55,7 @@ static inline int landlock_restrict_self(const int ruleset_fd,
>  #define ENV_FS_RW_NAME "LL_FS_RW"
>  #define ENV_TCP_BIND_NAME "LL_TCP_BIND"
>  #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
> +#define ENV_TCP_LISTEN_NAME "LL_TCP_LISTEN"
>  #define ENV_DELIMITER ":"
>  
>  static int parse_path(char *env_path, const char ***const path_list)
> @@ -208,7 +209,7 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>  
>  /* clang-format on */
>  
> -#define LANDLOCK_ABI_LAST 5
> +#define LANDLOCK_ABI_LAST 6
>  
>  int main(const int argc, char *const argv[], char *const *const envp)
>  {
> @@ -222,15 +223,16 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  	struct landlock_ruleset_attr ruleset_attr = {
>  		.handled_access_fs = access_fs_rw,
>  		.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
> -				      LANDLOCK_ACCESS_NET_CONNECT_TCP,
> +				      LANDLOCK_ACCESS_NET_CONNECT_TCP |
> +				      LANDLOCK_ACCESS_NET_LISTEN_TCP,
>  	};
>  
>  	if (argc < 2) {
>  		fprintf(stderr,
> -			"usage: %s=\"...\" %s=\"...\" %s=\"...\" %s=\"...\"%s "
> +			"usage: %s=\"...\" %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]);
> +			ENV_TCP_CONNECT_NAME, ENV_TCP_LISTEN_NAME, argv[0]);
>  		fprintf(stderr,
>  			"Execute a command in a restricted environment.\n\n");
>  		fprintf(stderr,
> @@ -251,15 +253,19 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  		fprintf(stderr,
>  			"* %s: list of ports allowed to connect (client).\n",
>  			ENV_TCP_CONNECT_NAME);
> +		fprintf(stderr,
> +			"* %s: list of ports allowed to listen (server).\n",
> +			ENV_TCP_LISTEN_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=\"9418\" "
>  			"%s bash -i\n\n",
>  			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
> -			ENV_TCP_CONNECT_NAME, argv[0]);
> +			ENV_TCP_CONNECT_NAME, ENV_TCP_LISTEN_NAME, argv[0]);
>  		fprintf(stderr,
>  			"This sandboxer can use Landlock features "
>  			"up to ABI version %d.\n",
> @@ -326,6 +332,11 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  	case 4:
>  		/* Removes LANDLOCK_ACCESS_FS_IOCTL_DEV for ABI < 5 */
>  		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_IOCTL_DEV;
> +		__attribute__((fallthrough));
> +	case 5:
> +		/* Removes LANDLOCK_ACCESS_NET_LISTEN support for ABI < 6 */
> +		ruleset_attr.handled_access_net &=
> +			~(LANDLOCK_ACCESS_NET_LISTEN_TCP);

(same remark as on other patch set)

ABI version has shifted by one in the meantime.

>  
>  		fprintf(stderr,
>  			"Hint: You should update the running kernel "
> @@ -357,6 +368,12 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  		ruleset_attr.handled_access_net &=
>  			~LANDLOCK_ACCESS_NET_CONNECT_TCP;
>  	}
> +	/* Removes listen access attribute if not supported by a user. */

(also same remark as on other patch set)

Please s/supported/requested/, for consistency.

> +	env_port_name = getenv(ENV_TCP_LISTEN_NAME);
> +	if (!env_port_name) {
> +		ruleset_attr.handled_access_net &=
> +			~LANDLOCK_ACCESS_NET_LISTEN_TCP;
> +	}
>  
>  	ruleset_fd =
>  		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
> @@ -380,6 +397,10 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  				 LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
>  		goto err_close_ruleset;
>  	}
> +	if (populate_ruleset_net(ENV_TCP_LISTEN_NAME, ruleset_fd,
> +				 LANDLOCK_ACCESS_NET_LISTEN_TCP)) {
> +		goto err_close_ruleset;
> +	}
>  
>  	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
>  		perror("Failed to restrict privileges");
> -- 
> 2.34.1
> 

Reviewed-by: Günther Noack <[email-masked]>