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

["Mickaël Salaün" <mic@digikod.net>]

On 10/09/2022 22:59, Konstantin Meskhidze (A) wrote:
> 
> 
> 9/6/2022 11:10 AM, Mickaël Salaün пишет:
>>
>> 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).
>>
>    So at the beginning there will be full network ruleset attribute
> supported:
>    .handled_access_net = LANDLOCK_ACCESS_NET_BIND_TCP |
>                          LANDLOCK_ACCESS_NET_CONNECT_TCP;
>    Correct?

yes


> 
>>
>>>    	};
>>>
>>>    	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.
> 
>     So I need to add refactored code into documentation?

yes