[PATCH v8 11/12] samples/landlock: Add network demo
Konstantin Meskhidze (A)
konstantin.meskhidze at huawei.com
Thu Jan 5 03:46:24 UTC 2023
11/16/2022 5:25 PM, Mickaël Salaün пишет:
>
> On 21/10/2022 17:26, 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 at huawei.com>
>> ---
>>
>> 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 | 129 +++++++++++++++++++++++++++++++----
>> 1 file changed, 116 insertions(+), 13 deletions(-)
>>
>> diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
>> index fd4237c64fb2..68582b0d7c85 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;
>
> This is a bug because env_port_name is not allocated. This should simply
> 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;
>> + 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 ( \
>> @@ -164,41 +222,63 @@ static int populate_ruleset(const char *const env_var, const int ruleset_fd,
>> LANDLOCK_ACCESS_FS_REFER | \
>> LANDLOCK_ACCESS_FS_TRUNCATE)
>>
>> +#define ACCESS_NET_BIND_CONNECT ( \
>> + LANDLOCK_ACCESS_NET_BIND_TCP | \
>> + LANDLOCK_ACCESS_NET_CONNECT_TCP)
>
> You can remove ACCESS_NET_BIND_CONNECT and make the underlying access
> rights explicit.
>
>
>> +
>> /* 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;
>> + access_fs_rw = ACCESS_FS_ROUGHLY_READ | ACCESS_FS_ROUGHLY_WRITE,
>> + access_net_tcp = ACCESS_NET_BIND_CONNECT;
>> struct landlock_ruleset_attr ruleset_attr = {
>> .handled_access_fs = access_fs_rw,
>> + .handled_access_net = access_net_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",
>> @@ -240,7 +320,10 @@ 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 &= ~ACCESS_NET_BIND_CONNECT;
>
> You can check the TCP environment variables here and error out if one is
> set.
>
> Please keep the newline here.
>
>
>> fprintf(stderr,
>> "Hint: You should update the running kernel "
>> "to leverage Landlock features "
>> @@ -259,16 +342,36 @@ 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) {
>
> You can move this logic at the populate_ruleset_net() call site and
> update this helper to not call getenv() twice for the same variable.
But here I exclude ruleset attributes, not rule itself. It will break
the logic: creating a ruleset then applying rules.
I suggest to leave here as its.
>
>
>> + access_net_tcp &= ~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) {
>> + access_net_tcp &= ~LANDLOCK_ACCESS_NET_CONNECT_TCP;
>> + }
>> + ruleset_attr.handled_access_net &= access_net_tcp;
>
> There is no need for access_net_tcp.
>
>> +
>> ruleset_fd =
>> landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
>> if (ruleset_fd < 0) {
>> perror("Failed to create a ruleset");
>> return 1;
>> }
>
> newline
>
>> - 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;
>> + }
>
> newline
>
>> + 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;
>> }
>
> newline
>
>> if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) {
>> --
>> 2.25.1
>>
> .
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