Subject: Re: [RFC PATCH v3 18/19] samples/landlock: Support socket protocol restrictions

From: "Günther Noack" <[email-masked]>
Date: Tue, 1 Oct 2024 09:56:52 +0200

On Wed, Sep 04, 2024 at 06:48:23PM +0800, Mikhail Ivanov wrote:
> Add socket protocol control support in sandboxer demo. It's possible
> to allow a sandboxer to create sockets with specified family and type
> values. This is controlled with the new LL_SOCKET_CREATE environment
> variable. Single token in this variable looks like this:
> 'FAMILY.TYPE', where FAMILY and TYPE are integers corresponding to the
> number of address family and socket type.
> 
> Add parse_socket_protocol() method to parse socket family and type
> strings into integers.
> 
> Change LANDLOCK_ABI_LAST to 6.
> 
> Signed-off-by: Mikhail Ivanov <[email-masked]>
> ---
> Changes since v2:
> * Changes representation of socket protocol in LL_SOCKET_CREATE into
>   pair of integer values.
> * Changes commit message.
> * Minor fixes.
> 
> Changes since v1:
> * Refactors get_socket_protocol(). Rename it to parse_socket_protocol().
> * Changes LANDLOCK_ABI_LAST to 6 since ioctl patchlist updated it to 5.
> * Refactors commit message.
> * Formats with clang-format.
> * Minor changes.
> ---
>  samples/landlock/sandboxer.c | 108 ++++++++++++++++++++++++++++++-----
>  1 file changed, 95 insertions(+), 13 deletions(-)
> 
> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> index d4dba9e4ce89..1669095f9373 100644
> --- a/samples/landlock/sandboxer.c
> +++ b/samples/landlock/sandboxer.c
> @@ -14,6 +14,7 @@
>  #include <fcntl.h>
>  #include <linux/landlock.h>
>  #include <linux/prctl.h>
> +#include <linux/socket.h>
>  #include <stddef.h>
>  #include <stdio.h>
>  #include <stdlib.h>
> @@ -55,8 +56,11 @@ 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_SOCKET_CREATE_NAME "LL_SOCKET_CREATE"
>  #define ENV_DELIMITER ":"
>  
> +#define ENV_TOKEN_INTERNAL_DELIMITER "."
> +
>  static int parse_path(char *env_path, const char ***const path_list)
>  {
>  	int i, num_paths = 0;
> @@ -209,6 +213,65 @@ static int populate_ruleset_net(const char *const env_var, const int ruleset_fd,
>  	return ret;
>  }
>  
> +static int populate_ruleset_socket(const char *const env_var,
> +				   const int ruleset_fd,
> +				   const __u64 allowed_access)
> +{
> +	int ret = 1;
> +	char *env_protocol_name, *strprotocol, *strfamily, *strtype;
> +	unsigned long long family_ull, type_ull;
> +	struct landlock_socket_attr protocol = {
> +		.allowed_access = allowed_access,
> +	};
> +
> +	env_protocol_name = getenv(env_var);
> +	if (!env_protocol_name)
> +		return 0;
> +	env_protocol_name = strdup(env_protocol_name);
> +	unsetenv(env_var);
> +
> +	while ((strprotocol = strsep(&env_protocol_name, ENV_DELIMITER))) {
> +		strfamily = strsep(&strprotocol, ENV_TOKEN_INTERNAL_DELIMITER);
> +		strtype = strsep(&strprotocol, ENV_TOKEN_INTERNAL_DELIMITER);

This works with strings such as "123:456:foobar", because you are using strsep()
twice on strprotocol; this looks unintentional?

> +
> +		if (!strtype) {
> +			fprintf(stderr,
> +				"Failed to extract socket protocol with "
> +				"unspecified type value\n");
> +			goto out_free_name;
> +		}
> +
> +		if (str2num(strfamily, &family_ull)) {
> +			fprintf(stderr,
> +				"Failed to convert \"%s\" into a number\n",
> +				strfamily);
> +			goto out_free_name;
> +		}
> +		if (str2num(strtype, &type_ull)) {
> +			fprintf(stderr,
> +				"Failed to convert \"%s\" into a number\n",
> +				strtype);
> +			goto out_free_name;
> +		}
> +		protocol.family = (int)family_ull;
> +		protocol.type = (int)type_ull;
> +
> +		if (landlock_add_rule(ruleset_fd, LANDLOCK_RULE_SOCKET,
> +				      &protocol, 0)) {
> +			fprintf(stderr,
> +				"Failed to update the ruleset with "
> +				"family \"%s\" and type \"%s\": %s\n",
> +				strfamily, strtype, strerror(errno));
> +			goto out_free_name;
> +		}
> +	}
> +	ret = 0;
> +
> +out_free_name:
> +	free(env_protocol_name);
> +	return ret;
> +}
> +
>  /* clang-format off */
>  
>  #define ACCESS_FS_ROUGHLY_READ ( \
> @@ -233,14 +296,14 @@ 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)
>  {
>  	const char *cmd_path;
>  	char *const *cmd_argv;
>  	int ruleset_fd, abi;
> -	char *env_port_name;
> +	char *env_optional_name;
>  	__u64 access_fs_ro = ACCESS_FS_ROUGHLY_READ,
>  	      access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE;
>  
> @@ -248,18 +311,19 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  		.handled_access_fs = access_fs_rw,
>  		.handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
>  				      LANDLOCK_ACCESS_NET_CONNECT_TCP,
> +		.handled_access_socket = LANDLOCK_ACCESS_SOCKET_CREATE,
>  	};
>  
>  	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_SOCKET_CREATE_NAME, argv[0]);
>  		fprintf(stderr,
>  			"Execute a command in a restricted environment.\n\n");
>  		fprintf(stderr,
> -			"Environment variables containing paths and ports "
> +			"Environment variables containing paths, ports and protocols "
>  			"each separated by a colon:\n");
>  		fprintf(stderr,
>  			"* %s: list of paths allowed to be used in a read-only way.\n",
> @@ -268,7 +332,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  			"* %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 "
> +			"Environment variables containing ports or protocols are optional "
>  			"and could be skipped.\n");
>  		fprintf(stderr,
>  			"* %s: list of ports allowed to bind (server).\n",
> @@ -276,15 +340,19 @@ 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 socket protocols allowed to be created.\n",
> +			ENV_SOCKET_CREATE_NAME);

Might be worth listing some example values for this parameter, e.g. for TCP/IP
and UDP/IP?  This is also needed to make it clear that these can't be given by
name, but only by number.

>  		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=\"10.2:1.1\" "
>  			"%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_SOCKET_CREATE_NAME, argv[0]);
>  		fprintf(stderr,
>  			"This sandboxer can use Landlock features "
>  			"up to ABI version %d.\n",
> @@ -351,7 +419,11 @@ 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 socket support for ABI < 6 */
> +		ruleset_attr.handled_access_socket &=
> +			~LANDLOCK_ACCESS_SOCKET_CREATE;
>  		fprintf(stderr,
>  			"Hint: You should update the running kernel "
>  			"to leverage Landlock features "
> @@ -371,18 +443,23 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  	access_fs_rw &= ruleset_attr.handled_access_fs;
>  
>  	/* Removes bind access attribute if not supported by a user. */
> -	env_port_name = getenv(ENV_TCP_BIND_NAME);
> -	if (!env_port_name) {
> +	env_optional_name = getenv(ENV_TCP_BIND_NAME);
> +	if (!env_optional_name) {
>  		ruleset_attr.handled_access_net &=
>  			~LANDLOCK_ACCESS_NET_BIND_TCP;
>  	}
>  	/* Removes connect access attribute if not supported by a user. */
> -	env_port_name = getenv(ENV_TCP_CONNECT_NAME);
> -	if (!env_port_name) {
> +	env_optional_name = getenv(ENV_TCP_CONNECT_NAME);
> +	if (!env_optional_name) {
>  		ruleset_attr.handled_access_net &=
>  			~LANDLOCK_ACCESS_NET_CONNECT_TCP;
>  	}
> -
> +	/* Removes socket create access attribute if not supported by a user. */

Phrasing nit: I would say "requested by a user"?

(And maybe also in the two cases above)

> +	env_optional_name = getenv(ENV_SOCKET_CREATE_NAME);
> +	if (!env_optional_name) {
> +		ruleset_attr.handled_access_socket &=
> +			~LANDLOCK_ACCESS_SOCKET_CREATE;
> +	}
>  	ruleset_fd =
>  		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
>  	if (ruleset_fd < 0) {
> @@ -406,6 +483,11 @@ int main(const int argc, char *const argv[], char *const *const envp)
>  		goto err_close_ruleset;
>  	}
>  
> +	if (populate_ruleset_socket(ENV_SOCKET_CREATE_NAME, ruleset_fd,
> +				    LANDLOCK_ACCESS_SOCKET_CREATE)) {
> +		goto err_close_ruleset;
> +	}
> +
>  	if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
>  		perror("Failed to restrict privileges");
>  		goto err_close_ruleset;
> -- 
> 2.34.1
> 

As I also said on the Documentation patch, please remember to double check the
places where the ABI number is mentioned, after rebasing on Tahera's "scoped"
patches.

—Günther