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Message-ID: <2ff97355-18ef-e539-b4c1-720cd83daf1d@digikod.net>
Date: Wed, 16 Nov 2022 15:25:57 +0100
From: Mickaël Salaün <mic@...ikod.net>
To: Konstantin Meskhidze <konstantin.meskhidze@...wei.com>
Cc: willemdebruijn.kernel@...il.com, gnoack3000@...il.com,
linux-security-module@...r.kernel.org, netdev@...r.kernel.org,
netfilter-devel@...r.kernel.org, artem.kuzin@...wei.com
Subject: Re: [PATCH v8 11/12] samples/landlock: Add network demo
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@...wei.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.
> + 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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