Re: [PATCH v7 17/18] samples/landlock: add network demo

["Mickaël Salaün" <mic@digikod.net>]

On 29/08/2022 19:04, Konstantin Meskhidze wrote:
> This commit adds network demo. It's possible to allow a sandboxer to
> bind/connect to a list of particular ports restricting network
> actions to the rest of ports.
> 
> Signed-off-by: Konstantin Meskhidze <konstantin.meskhidze@huawei.com>
> ---
> 
> Changes since v6:
> * Removes network support if ABI < 3.
> 
> Changes since v5:
> * Makes network ports sandboxing optional.
> * Fixes some logic errors.
> * Formats code with clang-format-14.
> 
> Changes since v4:
> * Adds ENV_TCP_BIND_NAME "LL_TCP_BIND" and
> ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT" variables
> to insert TCP ports.
> * Renames populate_ruleset() to populate_ruleset_fs().
> * Adds populate_ruleset_net() and parse_port_num() helpers.
> * Refactors main() to support network sandboxing.
> 
> ---
>   samples/landlock/sandboxer.c | 123 +++++++++++++++++++++++++++++++----
>   1 file changed, 112 insertions(+), 11 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index 771b6b10d519..7f88067534df 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -51,6 +51,8 @@ static inline int landlock_restrict_self(const int ruleset_fd,
> 
>   #define ENV_FS_RO_NAME "LL_FS_RO"
>   #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_PATH_TOKEN ":"
> 
>   static int parse_path(char *env_path, const char ***const path_list)
> @@ -71,6 +73,20 @@ static int parse_path(char *env_path, const char ***const path_list)
>   	return num_paths;
>   }
> 
> +static int parse_port_num(char *env_port)
> +{
> +	int i, num_ports = 0;
> +
> +	if (env_port) {
> +		num_ports++;
> +		for (i = 0; env_port[i]; i++) {
> +			if (env_port[i] == ENV_PATH_TOKEN[0])
> +				num_ports++;
> +		}
> +	}
> +	return num_ports;
> +}
> +
>   /* clang-format off */
> 
>   #define ACCESS_FILE ( \
> @@ -81,8 +97,8 @@ static int parse_path(char *env_path, const char ***const path_list)
> 
>   /* clang-format on */
> 
> -static int populate_ruleset(const char *const env_var, const int ruleset_fd,
> -			    const __u64 allowed_access)
> +static int populate_ruleset_fs(const char *const env_var, const int ruleset_fd,
> +			       const __u64 allowed_access)
>   {
>   	int num_paths, i, ret = 1;
>   	char *env_path_name;
> @@ -143,6 +159,48 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
>   	return ret;
>   }
> 
> +static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
> +				const __u64 allowed_access)
> +{
> +	int num_ports, i, ret = 1;
> +	char *env_port_name;
> +	struct landlock_net_service_attr net_service = {
> +		.allowed_access = 0,
> +		.port = 0,
> +	};
> +
> +	env_port_name = getenv(env_var);
> +	if (!env_port_name) {
> +		ret = 0;
> +		goto out_free_name;
> +	}
> +	env_port_name = strdup(env_port_name);
> +	unsetenv(env_var);
> +	num_ports = parse_port_num(env_port_name);
> +
> +	if (num_ports == 1 && (strtok(env_port_name, ENV_PATH_TOKEN) == NULL)) {
> +		ret = 0;
> +		goto out_free_name;
> +	}
> +
> +	for (i = 0; i < num_ports; i++) {
> +		net_service.allowed_access = allowed_access;
> +		net_service.port = atoi(strsep(&env_port_name, ENV_PATH_TOKEN));
> +		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_NET_SERVICE,
> +				      &net_service, 0)) {
> +			fprintf(stderr,
> +				"Failed to update the ruleset with port \"%d\": %s\n",
> +				net_service.port, strerror(errno));
> +			goto out_free_name;
> +		}
> +	}
> +	ret = 0;
> +
> +out_free_name:
> +	free(env_port_name);
> +	return ret;
> +}
> +
>   /* clang-format off */
> 
>   #define ACCESS_FS_ROUGHLY_READ ( \
> @@ -171,32 +229,50 @@ int main(const int argc, char *const argv[], char *const *const envp)
>   	const char *cmd_path;
>   	char *const *cmd_argv;
>   	int ruleset_fd, abi;
> +	char *env_port_name;
>   	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
> -	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
> +	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE,
> +	      access_net_tcp = 0;
>   	struct landlock_ruleset_attr ruleset_attr = {
>   		.handled_access_fs = access_fs_rw,
> +		.handled_access_net = access_net_tcp,

Please follow the same logic as for handled_access_fs: by default 
handles all accesses, then remove the ones that are not supported by the 
kernel, then remove the ones that are not explicitly set by users (by 
checking env_port_name).


>   	};
> 
>   	if (argc < 2) {
>   		fprintf(stderr,
> -			"usage: %s=\"...\" %s=\"...\" %s <cmd> [args]...\n\n",
> -			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
> +			"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,
>   			"Launch a command in a restricted environment.\n\n");
> -		fprintf(stderr, "Environment variables containing paths, "
> -				"each separated by a colon:\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",
> +			"* %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=\"/bin:/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",
> -			ENV_FS_RO_NAME, ENV_FS_RW_NAME, argv[0]);
> +			ENV_FS_RO_NAME, ENV_FS_RW_NAME, ENV_TCP_BIND_NAME,
> +			ENV_TCP_CONNECT_NAME, argv[0]);
>   		return 1;
>   	}
> 
> @@ -224,15 +300,32 @@ int main(const int argc, char *const argv[], char *const *const envp)
>   		}
>   		return 1;
>   	}
> +
> +	/* Adds optionally network bind() support. */
> +	env_port_name = getenv(ENV_TCP_BIND_NAME);
> +	if (env_port_name) {
> +		access_net_tcp |= LANDLOCK_ACCESS_NET_BIND_TCP;
> +	}
> +	/* Adds optionally network connect() support. */
> +	env_port_name = getenv(ENV_TCP_CONNECT_NAME);
> +	if (env_port_name) {
> +		access_net_tcp |= LANDLOCK_ACCESS_NET_CONNECT_TCP;
> +	}
> +	ruleset_attr.handled_access_net = access_net_tcp;
> +
>   	/* Best-effort security. */
>   	switch (abi) {
>   	case 1:
>   		/* Removes LANDLOCK_ACCESS_FS_REFER for ABI < 2 */
>   		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_REFER;
> +		/* Removes network support for ABI < 2 */
> +		ruleset_attr.handled_access_net = 0;

Same issue as for the documentation.


>   		__attribute__((fallthrough));
>   	case 2:
>   		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
>   		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
> +		/* Removes network support for ABI < 3 */
> +		ruleset_attr.handled_access_net = 0;
>   	}
>   	access_fs_ro &= ruleset_attr.handled_access_fs;
>   	access_fs_rw &= ruleset_attr.handled_access_fs;
> @@ -243,10 +336,18 @@ int main(const int argc, char *const argv[], char *const *const envp)
>   		perror("Failed to create a ruleset");
>   		return 1;
>   	}
> -	if (populate_ruleset(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
> +	if (populate_ruleset_fs(ENV_FS_RO_NAME, ruleset_fd, access_fs_ro)) {
> +		goto err_close_ruleset;
> +	}
> +	if (populate_ruleset_fs(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
> +		goto err_close_ruleset;
> +	}
> +	if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
> +				 LANDLOCK_ACCESS_NET_BIND_TCP)) {
>   		goto err_close_ruleset;
>   	}
> -	if (populate_ruleset(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
> +	if (populate_ruleset_net(ENV_TCP_CONNECT_NAME, ruleset_fd,
> +				 LANDLOCK_ACCESS_NET_CONNECT_TCP)) {
>   		goto err_close_ruleset;
>   	}
>   	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
> --
> 2.25.1
>