diff --git a/Documentation/security/landlock.rst b/Documentation/security/landlock.rst index 3e4d4d04cfae..c5186526e76f 100644 --- a/Documentation/security/landlock.rst +++ b/Documentation/security/landlock.rst @@ -7,7 +7,7 @@ Landlock LSM: kernel documentation ================================== :Author: Mickaël Salaün -:Date: September 2025 +:Date: March 2026 Landlock's goal is to create scoped access-control (i.e. sandboxing). To harden a whole system, this feature should be available to any process, @@ -89,6 +89,46 @@ this is required to keep access controls consistent over the whole system, and this avoids unattended bypasses through file descriptor passing (i.e. confused deputy attack). +.. _scoped-flags-interaction: + +Interaction between scoped flags and other access rights +-------------------------------------------------------- + +The ``scoped`` flags in &struct landlock_ruleset_attr restrict the +use of *outgoing* IPC from the created Landlock domain, while they +permit reaching out to IPC endpoints *within* the created Landlock +domain. + +In the future, scoped flags *may* interact with other access rights, +e.g. so that abstract UNIX sockets can be allow-listed by name, or so +that signals can be allow-listed by signal number or target process. + +When introducing ``LANDLOCK_ACCESS_FS_RESOLVE_UNIX``, we defined it to +implicitly have the same scoping semantics as a +``LANDLOCK_SCOPE_PATHNAME_UNIX_SOCKET`` flag would have: connecting to +UNIX sockets within the same domain (where +``LANDLOCK_ACCESS_FS_RESOLVE_UNIX`` is used) is unconditionally +allowed. + +The reasoning is: + +* Like other IPC mechanisms, connecting to named UNIX sockets in the + same domain should be expected and harmless. (If needed, users can + further refine their Landlock policies with nested domains or by + restricting ``LANDLOCK_ACCESS_FS_MAKE_SOCK``.) +* We reserve the option to still introduce + ``LANDLOCK_SCOPE_PATHNAME_UNIX_SOCKET`` in the future. (This would + be useful if we wanted to have a Landlock rule to permit IPC access + to other Landlock domains.) +* But we can postpone the point in time when users have to deal with + two interacting flags visible in the userspace API. (In particular, + it is possible that it won't be needed in practice, in which case we + can avoid the second flag altogether.) +* If we *do* introduce ``LANDLOCK_SCOPE_PATHNAME_UNIX_SOCKET`` in the + future, setting this scoped flag in a ruleset does *not reduce* the + restrictions, because access within the same scope is already + allowed based on ``LANDLOCK_ACCESS_FS_RESOLVE_UNIX``. + Tests ===== diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index d37603efc273..10a346e55e95 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -250,6 +250,26 @@ struct landlock_net_port_attr { * * This access right is available since the fifth version of the Landlock * ABI. + * - %LANDLOCK_ACCESS_FS_RESOLVE_UNIX: Look up pathname UNIX domain sockets + * (:manpage:`unix(7)`). On UNIX domain sockets, this restricts both calls to + * :manpage:`connect(2)` as well as calls to :manpage:`sendmsg(2)` with an + * explicit recipient address. + * + * This access right only applies to connections to UNIX server sockets which + * were created outside of the newly created Landlock domain (e.g. from within + * a parent domain or from an unrestricted process). Newly created UNIX + * servers within the same Landlock domain continue to be accessible. In this + * regard, %LANDLOCK_ACCESS_FS_RESOLVE_UNIX has the same semantics as the + * ``LANDLOCK_SCOPE_*`` flags. + * + * If a resolve attempt is denied, the operation returns an ``EACCES`` error, + * in line with other filesystem access rights (but different to denials for + * abstract UNIX domain sockets). + * + * This access right is available since the ninth version of the Landlock ABI. + * + * The rationale for this design is described in + * :ref:`Documentation/security/landlock.rst `. * * Whether an opened file can be truncated with :manpage:`ftruncate(2)` or used * with `ioctl(2)` is determined during :manpage:`open(2)`, in the same way as @@ -335,6 +355,7 @@ struct landlock_net_port_attr { #define LANDLOCK_ACCESS_FS_REFER (1ULL << 13) #define LANDLOCK_ACCESS_FS_TRUNCATE (1ULL << 14) #define LANDLOCK_ACCESS_FS_IOCTL_DEV (1ULL << 15) +#define LANDLOCK_ACCESS_FS_RESOLVE_UNIX (1ULL << 16) /* clang-format on */ /** diff --git a/security/landlock/access.h b/security/landlock/access.h index 42c95747d7bd..c19d5bc13944 100644 --- a/security/landlock/access.h +++ b/security/landlock/access.h @@ -34,7 +34,7 @@ LANDLOCK_ACCESS_FS_IOCTL_DEV) /* clang-format on */ -typedef u16 access_mask_t; +typedef u32 access_mask_t; /* Makes sure all filesystem access rights can be stored. */ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS); @@ -50,7 +50,7 @@ struct access_masks { access_mask_t fs : LANDLOCK_NUM_ACCESS_FS; access_mask_t net : LANDLOCK_NUM_ACCESS_NET; access_mask_t scope : LANDLOCK_NUM_SCOPE; -}; +} __packed __aligned(sizeof(u32)); union access_masks_all { struct access_masks masks; diff --git a/security/landlock/audit.c b/security/landlock/audit.c index 60ff217ab95b..8d0edf94037d 100644 --- a/security/landlock/audit.c +++ b/security/landlock/audit.c @@ -37,6 +37,7 @@ static const char *const fs_access_strings[] = { [BIT_INDEX(LANDLOCK_ACCESS_FS_REFER)] = "fs.refer", [BIT_INDEX(LANDLOCK_ACCESS_FS_TRUNCATE)] = "fs.truncate", [BIT_INDEX(LANDLOCK_ACCESS_FS_IOCTL_DEV)] = "fs.ioctl_dev", + [BIT_INDEX(LANDLOCK_ACCESS_FS_RESOLVE_UNIX)] = "fs.resolve_unix", }; static_assert(ARRAY_SIZE(fs_access_strings) == LANDLOCK_NUM_ACCESS_FS); diff --git a/security/landlock/fs.c b/security/landlock/fs.c index 97065d51685a..fcf69b3d734d 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -27,6 +27,7 @@ #include #include #include +#include #include #include #include @@ -36,6 +37,7 @@ #include #include #include +#include #include #include @@ -314,7 +316,8 @@ static struct landlock_object *get_inode_object(struct inode *const inode) LANDLOCK_ACCESS_FS_WRITE_FILE | \ LANDLOCK_ACCESS_FS_READ_FILE | \ LANDLOCK_ACCESS_FS_TRUNCATE | \ - LANDLOCK_ACCESS_FS_IOCTL_DEV) + LANDLOCK_ACCESS_FS_IOCTL_DEV | \ + LANDLOCK_ACCESS_FS_RESOLVE_UNIX) /* clang-format on */ /* @@ -1557,6 +1560,130 @@ static int hook_path_truncate(const struct path *const path) return current_check_access_path(path, LANDLOCK_ACCESS_FS_TRUNCATE); } +/** + * unmask_scoped_access - Remove access right bits in @masks in all layers + * where @client and @server have the same domain + * + * This does the same as domain_is_scoped(), but unmasks bits in @masks. + * It can not return early as domain_is_scoped() does. + * + * A scoped access for a given access right bit is allowed iff, for all layer + * depths where the access bit is set, the client and server domain are the + * same. This function clears the access rights @access in @masks at all layer + * depths where the client and server domain are the same, so that, when they + * are all cleared, the access is allowed. + * + * @client: Client domain + * @server: Server domain + * @masks: Layer access masks to unmask + * @access: Access bits that control scoping + */ +static void unmask_scoped_access(const struct landlock_ruleset *const client, + const struct landlock_ruleset *const server, + struct layer_access_masks *const masks, + const access_mask_t access) +{ + int client_layer, server_layer; + const struct landlock_hierarchy *client_walker, *server_walker; + + /* This should not happen. */ + if (WARN_ON_ONCE(!client)) + return; + + /* Server has no Landlock domain; nothing to clear. */ + if (!server) + return; + + /* + * client_layer must be a signed integer with greater capacity + * than client->num_layers to ensure the following loop stops. + */ + BUILD_BUG_ON(sizeof(client_layer) > sizeof(client->num_layers)); + + client_layer = client->num_layers - 1; + client_walker = client->hierarchy; + server_layer = server->num_layers - 1; + server_walker = server->hierarchy; + + /* + * Clears the access bits at all layers where the client domain is the + * same as the server domain. We start the walk at min(client_layer, + * server_layer). The layer bits until there can not be cleared because + * either the client or the server domain is missing. + */ + for (; client_layer > server_layer; client_layer--) + client_walker = client_walker->parent; + + for (; server_layer > client_layer; server_layer--) + server_walker = server_walker->parent; + + for (; client_layer >= 0; client_layer--) { + if (masks->access[client_layer] & access && + client_walker == server_walker) + masks->access[client_layer] &= ~access; + + client_walker = client_walker->parent; + server_walker = server_walker->parent; + } +} + +static int hook_unix_find(const struct path *const path, struct sock *other, + int flags) +{ + const struct landlock_ruleset *dom_other; + const struct landlock_cred_security *subject; + struct layer_access_masks layer_masks; + struct landlock_request request = {}; + static const struct access_masks fs_resolve_unix = { + .fs = LANDLOCK_ACCESS_FS_RESOLVE_UNIX, + }; + + /* Lookup for the purpose of saving coredumps is OK. */ + if (unlikely(flags & SOCK_COREDUMP)) + return 0; + + subject = landlock_get_applicable_subject(current_cred(), + fs_resolve_unix, NULL); + + if (!subject) + return 0; + + /* + * Ignoring return value: that the domains apply was already checked in + * landlock_get_applicable_subject() above. + */ + landlock_init_layer_masks(subject->domain, fs_resolve_unix.fs, + &layer_masks, LANDLOCK_KEY_INODE); + + /* Checks the layers in which we are connecting within the same domain. */ + unix_state_lock(other); + if (unlikely(sock_flag(other, SOCK_DEAD) || !other->sk_socket || + !other->sk_socket->file)) { + unix_state_unlock(other); + /* + * We rely on the caller to catch the (non-reversible) SOCK_DEAD + * condition and retry the lookup. If we returned an error + * here, the lookup would not get retried. + */ + return 0; + } + dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain; + + /* Access to the same (or a lower) domain is always allowed. */ + unmask_scoped_access(subject->domain, dom_other, &layer_masks, + fs_resolve_unix.fs); + unix_state_unlock(other); + + /* Checks the connections to allow-listed paths. */ + if (is_access_to_paths_allowed(subject->domain, path, + fs_resolve_unix.fs, &layer_masks, + &request, NULL, 0, NULL, NULL, NULL)) + return 0; + + landlock_log_denial(subject, &request); + return -EACCES; +} + /* File hooks */ /** @@ -1834,6 +1961,7 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = { LSM_HOOK_INIT(path_unlink, hook_path_unlink), LSM_HOOK_INIT(path_rmdir, hook_path_rmdir), LSM_HOOK_INIT(path_truncate, hook_path_truncate), + LSM_HOOK_INIT(unix_find, hook_unix_find), LSM_HOOK_INIT(file_alloc_security, hook_file_alloc_security), LSM_HOOK_INIT(file_open, hook_file_open), diff --git a/security/landlock/limits.h b/security/landlock/limits.h index eb584f47288d..b454ad73b15e 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -19,7 +19,7 @@ #define LANDLOCK_MAX_NUM_LAYERS 16 #define LANDLOCK_MAX_NUM_RULES U32_MAX -#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_IOCTL_DEV +#define LANDLOCK_LAST_ACCESS_FS LANDLOCK_ACCESS_FS_RESOLVE_UNIX #define LANDLOCK_MASK_ACCESS_FS ((LANDLOCK_LAST_ACCESS_FS << 1) - 1) #define LANDLOCK_NUM_ACCESS_FS __const_hweight64(LANDLOCK_MASK_ACCESS_FS) diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c index 5ebd606e84e6..accfd2e5a0cd 100644 --- a/security/landlock/syscalls.c +++ b/security/landlock/syscalls.c @@ -166,7 +166,7 @@ static const struct file_operations ruleset_fops = { * If the change involves a fix that requires userspace awareness, also update * the errata documentation in Documentation/userspace-api/landlock.rst . */ -const int landlock_abi_version = 8; +const int landlock_abi_version = 9; /** * sys_landlock_create_ruleset - Create a new ruleset diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c index 0fea236ef4bd..30d37234086c 100644 --- a/tools/testing/selftests/landlock/base_test.c +++ b/tools/testing/selftests/landlock/base_test.c @@ -76,7 +76,7 @@ TEST(abi_version) const struct landlock_ruleset_attr ruleset_attr = { .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, }; - ASSERT_EQ(8, landlock_create_ruleset(NULL, 0, + ASSERT_EQ(9, landlock_create_ruleset(NULL, 0, LANDLOCK_CREATE_RULESET_VERSION)); ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0, diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c index 968a91c927a4..b318627e7561 100644 --- a/tools/testing/selftests/landlock/fs_test.c +++ b/tools/testing/selftests/landlock/fs_test.c @@ -575,9 +575,10 @@ TEST_F_FORK(layout1, inval) LANDLOCK_ACCESS_FS_WRITE_FILE | \ LANDLOCK_ACCESS_FS_READ_FILE | \ LANDLOCK_ACCESS_FS_TRUNCATE | \ - LANDLOCK_ACCESS_FS_IOCTL_DEV) + LANDLOCK_ACCESS_FS_IOCTL_DEV | \ + LANDLOCK_ACCESS_FS_RESOLVE_UNIX) -#define ACCESS_LAST LANDLOCK_ACCESS_FS_IOCTL_DEV +#define ACCESS_LAST LANDLOCK_ACCESS_FS_RESOLVE_UNIX #define ACCESS_ALL ( \ ACCESS_FILE | \