Re: [PATCH v10 12/13] samples/landlock: Add network demo

["Konstantin Meskhidze (A)" <konstantin.meskhidze@xxxxxxxxxx>]

4/16/2023 7:13 PM, Mickaël Salaün пишет:
> On 23/03/2023 09:52, 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@xxxxxxxxxx>
> > ---
> >
> > Changes since v9:
> > * Deletes ports converting.
> > * Minor fixes.
> >
> > Changes since v8:
> > * Convert ports to __be16.
> > * Minor fixes.
> >
> > Changes since v7:
> > * Removes network support if ABI < 4.
> > * Removes network support if not set by a user.
> >
> > 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 | 130 +++++++++++++++++++++++++++++++----
> >   1 file changed, 118 insertions(+), 12 deletions(-)
> >
> > diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
> > index e2056c8b902c..b8f00e4dba95 100644
> > --- a/samples/landlock/sandboxer.c
> > +++ b/samples/landlock/sandboxer.c
> > @@ -8,6 +8,7 @@
> >    */
> >
> >   #define _GNU_SOURCE
> > +#include <arpa/inet.h>
> >   #include <errno.h>
> >   #include <fcntl.h>
> >   #include <linux/landlock.h>
> > @@ -51,6 +52,8 @@ 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 +74,20 @@ 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 +98,8 @@ 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 +160,47 @@ 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,
>
> .allowed_access = allowed_access,

  Got it.
> > +		.port = 0,
> > +	};
> > +
> > +	env_port_name = getenv(env_var);
> > +	if (!env_port_name) {
> > +		return 0;
> > +	}
> > +	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;
>
> This previous line can now be removed.

  Ok. Thanks for the tip.
> > +		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 \"%lld\": %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 ( \
> > @@ -166,39 +224,58 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
> >
> >   /* clang-format on */
> >
> > -#define LANDLOCK_ABI_LAST 3
> > +#define LANDLOCK_ABI_LAST 4
> >
> >   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;
> > +
> >   	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,
> >   	};
> >
> >   	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\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]);
> >   		fprintf(stderr,
> >   			"This sandboxer can use Landlock features "
> >   			"up to ABI version %d.\n",
> > @@ -255,7 +332,12 @@ int main(const int argc, char *const argv[], char *const *const envp)
> >   	case 2:
> >   		/* Removes LANDLOCK_ACCESS_FS_TRUNCATE for ABI < 3 */
> >   		ruleset_attr.handled_access_fs &= ~LANDLOCK_ACCESS_FS_TRUNCATE;
> > -
> > +		__attribute__((fallthrough));
> > +	case 3:
> > +		/* Removes network support for ABI < 4 */
> > +		ruleset_attr.handled_access_net &=
> > +			~(LANDLOCK_ACCESS_NET_BIND_TCP |
> > +			  LANDLOCK_ACCESS_NET_CONNECT_TCP);
> >   		fprintf(stderr,
> >   			"Hint: You should update the running kernel "
> >   			"to leverage Landlock features "
> > @@ -274,18 +356,42 @@ int main(const int argc, char *const argv[], char *const *const envp)
> >   	access_fs_ro &= ruleset_attr.handled_access_fs;
> >   	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) {
> > +		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) {
> > +		ruleset_attr.handled_access_net &=
> > +			~LANDLOCK_ACCESS_NET_CONNECT_TCP;
> > +	}
> > +
> >   	ruleset_fd =
> >   		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
> >   	if (ruleset_fd < 0) {
> >   		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(ENV_FS_RW_NAME, ruleset_fd, access_fs_rw)) {
> > +
> > +	if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
> > +				 LANDLOCK_ACCESS_NET_BIND_TCP)) {
> >   		goto err_close_ruleset;
> >   	}
> > +	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)) {
> >   		perror("Failed to restrict privileges");
> >   		goto err_close_ruleset;
> > --
> > 2.25.1
> .