Add audit support to the file_truncate and file_ioctl hooks. Add a deny_masks_t type and related helpers to store the domain's layer level per optional access rights (i.e. LANDLOCK_ACCESS_FS_TRUNCATE and LANDLOCK_ACCESS_FS_IOCTL_DEV) when opening a file, which cannot be inferred later. In practice, the landlock_file_security blob size is unchanged because this new one-byte deny_masks field follows the existing two-bytes allowed_access field.
Implementing deny_masks_t with a bitfield instead of a struct enables a generic implementation to store and extract layer levels. Add KUnit tests to check the identification of a layer level from a deny_masks_t, and the computation of a deny_masks_t from an access right with its layer level or a layer_mask_t array. Audit event sample: type=LANDLOCK_DENY msg=audit(1729738800.349:44): domain=195ba459b blockers=fs.ioctl_dev path="/dev/tty" dev="devtmpfs" ino=9 Cc: Günther Noack <[email protected]> Signed-off-by: Mickaël Salaün <[email protected]> Link: https://lore.kernel.org/r/[email protected] --- Changes since v3: - Rename get_layer_from_deny_masks(). Changes since v2: - Fix !CONFIG_AUDIT build warning. - Rename ACCESS_FS_OPTIONAL to _LANDLOCK_ACCESS_FS_OPTIONAL. --- security/landlock/access.h | 23 +++++++ security/landlock/audit.c | 102 ++++++++++++++++++++++++++-- security/landlock/audit.h | 4 ++ security/landlock/domain.c | 133 +++++++++++++++++++++++++++++++++++++ security/landlock/domain.h | 8 +++ security/landlock/fs.c | 51 ++++++++++++++ security/landlock/fs.h | 9 +++ 7 files changed, 325 insertions(+), 5 deletions(-) diff --git a/security/landlock/access.h b/security/landlock/access.h index 74fd8f399fbd..1eaaafa63178 100644 --- a/security/landlock/access.h +++ b/security/landlock/access.h @@ -28,6 +28,12 @@ LANDLOCK_ACCESS_FS_REFER) /* clang-format on */ +/* clang-format off */ +#define _LANDLOCK_ACCESS_FS_OPTIONAL ( \ + LANDLOCK_ACCESS_FS_TRUNCATE | \ + LANDLOCK_ACCESS_FS_IOCTL_DEV) +/* clang-format on */ + typedef u16 access_mask_t; /* Makes sure all filesystem access rights can be stored. */ @@ -60,6 +66,23 @@ typedef u16 layer_mask_t; /* Makes sure all layers can be checked. */ static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS); +/* + * Tracks domains responsible of a denied access. This is required to avoid + * storing in each object the full layer_masks[] required by update_request(). + */ +typedef u8 deny_masks_t; + +/* + * Makes sure all optional access rights can be tied to a layer index (cf. + * get_deny_mask). + */ +static_assert(BITS_PER_TYPE(deny_masks_t) >= + (HWEIGHT(LANDLOCK_MAX_NUM_LAYERS - 1) * + HWEIGHT(_LANDLOCK_ACCESS_FS_OPTIONAL))); + +/* LANDLOCK_MAX_NUM_LAYERS must be a power of two (cf. deny_masks_t assert). */ +static_assert(HWEIGHT(LANDLOCK_MAX_NUM_LAYERS) == 1); + /* Upgrades with all initially denied by default access rights. */ static inline struct access_masks landlock_upgrade_handled_access_masks(struct access_masks access_masks) diff --git a/security/landlock/audit.c b/security/landlock/audit.c index 987b4b15e0d7..89446e913d9f 100644 --- a/security/landlock/audit.c +++ b/security/landlock/audit.c @@ -13,9 +13,11 @@ #include <linux/uidgid.h> #include <uapi/linux/landlock.h> +#include "access.h" #include "audit.h" #include "common.h" #include "domain.h" +#include "fs.h" #include "ruleset.h" static const char *const fs_access_strings[] = { @@ -253,22 +255,111 @@ static void test_get_denied_layer(struct kunit *const test) #endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ +static size_t +get_layer_from_deny_masks(access_mask_t *const access_request, + const access_mask_t all_existing_optional_access, + const deny_masks_t deny_masks) +{ + const unsigned long access_opt = all_existing_optional_access; + const unsigned long access_req = *access_request; + access_mask_t missing = 0; + size_t youngest_layer = 0; + size_t access_index = 0; + unsigned long access_bit; + + /* This will require change with new object types. */ + WARN_ON_ONCE(access_opt != _LANDLOCK_ACCESS_FS_OPTIONAL); + + for_each_set_bit(access_bit, &access_opt, + BITS_PER_TYPE(access_mask_t)) { + if (access_req & BIT(access_bit)) { + const size_t layer = + (deny_masks >> (access_index * 4)) & + (LANDLOCK_MAX_NUM_LAYERS - 1); + + if (layer > youngest_layer) { + youngest_layer = layer; + missing = BIT(access_bit); + } else if (layer == youngest_layer) { + missing |= BIT(access_bit); + } + } + access_index++; + } + + *access_request = missing; + return youngest_layer; +} + +#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST + +static void test_get_layer_from_deny_masks(struct kunit *const test) +{ + deny_masks_t deny_mask; + access_mask_t access; + + /* truncate:0 ioctl_dev:2 */ + deny_mask = 0x20; + + access = LANDLOCK_ACCESS_FS_TRUNCATE; + KUNIT_EXPECT_EQ(test, 0, + get_layer_from_deny_masks(&access, + _LANDLOCK_ACCESS_FS_OPTIONAL, + deny_mask)); + KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_TRUNCATE); + + access = LANDLOCK_ACCESS_FS_TRUNCATE | LANDLOCK_ACCESS_FS_IOCTL_DEV; + KUNIT_EXPECT_EQ(test, 2, + get_layer_from_deny_masks(&access, + _LANDLOCK_ACCESS_FS_OPTIONAL, + deny_mask)); + KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_IOCTL_DEV); + + /* truncate:15 ioctl_dev:15 */ + deny_mask = 0xff; + + access = LANDLOCK_ACCESS_FS_TRUNCATE; + KUNIT_EXPECT_EQ(test, 15, + get_layer_from_deny_masks(&access, + _LANDLOCK_ACCESS_FS_OPTIONAL, + deny_mask)); + KUNIT_EXPECT_EQ(test, access, LANDLOCK_ACCESS_FS_TRUNCATE); + + access = LANDLOCK_ACCESS_FS_TRUNCATE | LANDLOCK_ACCESS_FS_IOCTL_DEV; + KUNIT_EXPECT_EQ(test, 15, + get_layer_from_deny_masks(&access, + _LANDLOCK_ACCESS_FS_OPTIONAL, + deny_mask)); + KUNIT_EXPECT_EQ(test, access, + LANDLOCK_ACCESS_FS_TRUNCATE | + LANDLOCK_ACCESS_FS_IOCTL_DEV); +} + +#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ + static bool is_valid_request(const struct landlock_request *const request) { if (WARN_ON_ONCE(!(!!request->layer_plus_one ^ !!request->access))) return false; if (request->access) { - if (WARN_ON_ONCE(!request->layer_masks)) + if (WARN_ON_ONCE(!(!!request->layer_masks ^ + !!request->all_existing_optional_access))) return false; } else { - if (WARN_ON_ONCE(request->layer_masks)) + if (WARN_ON_ONCE(request->layer_masks || + request->all_existing_optional_access)) return false; } if (WARN_ON_ONCE(!!request->layer_masks ^ !!request->layer_masks_size)) return false; + if (request->deny_masks) { + if (WARN_ON_ONCE(!request->all_existing_optional_access)) + return false; + } + return true; } @@ -301,9 +392,9 @@ void landlock_log_denial(const struct landlock_ruleset *const domain, domain, &missing, request->layer_masks, request->layer_masks_size); } else { - /* This will change with the next commit. */ - WARN_ON_ONCE(1); - youngest_layer = domain->num_layers; + youngest_layer = get_layer_from_deny_masks( + &missing, request->all_existing_optional_access, + request->deny_masks); } youngest_denied = get_hierarchy(domain, youngest_layer); } else { @@ -377,6 +468,7 @@ static struct kunit_case test_cases[] = { /* clang-format off */ KUNIT_CASE(test_get_hierarchy), KUNIT_CASE(test_get_denied_layer), + KUNIT_CASE(test_get_layer_from_deny_masks), {} /* clang-format on */ }; diff --git a/security/landlock/audit.h b/security/landlock/audit.h index 093791929580..762cdbd10b3a 100644 --- a/security/landlock/audit.h +++ b/security/landlock/audit.h @@ -42,6 +42,10 @@ struct landlock_request { /* Required fields for requests with layer masks. */ const layer_mask_t (*layer_masks)[]; size_t layer_masks_size; + + /* Required fields for requests with deny masks. */ + const access_mask_t all_existing_optional_access; + deny_masks_t deny_masks; }; #ifdef CONFIG_AUDIT diff --git a/security/landlock/domain.c b/security/landlock/domain.c index d0cb9f8683b4..f1a0d1b9af7c 100644 --- a/security/landlock/domain.c +++ b/security/landlock/domain.c @@ -7,6 +7,9 @@ * Copyright © 2024-2025 Microsoft Corporation */ +#include <kunit/test.h> +#include <linux/bitops.h> +#include <linux/bits.h> #include <linux/cred.h> #include <linux/file.h> #include <linux/landlock.h> @@ -16,6 +19,8 @@ #include <linux/sched.h> #include <linux/timekeeping.h> +#include "access.h" +#include "common.h" #include "domain.h" #include "fs.h" #include "id.h" @@ -153,4 +158,132 @@ int landlock_init_current_hierarchy(struct landlock_hierarchy *const hierarchy) return 0; } +static deny_masks_t +get_layer_deny_mask(const access_mask_t all_existing_optional_access, + const unsigned long access_bit, const size_t layer) +{ + unsigned long access_weight; + + /* This may require change with new object types. */ + WARN_ON_ONCE(all_existing_optional_access != + _LANDLOCK_ACCESS_FS_OPTIONAL); + + if (WARN_ON_ONCE(layer >= LANDLOCK_MAX_NUM_LAYERS)) + return 0; + + access_weight = hweight_long(all_existing_optional_access & + GENMASK(access_bit, 0)); + if (WARN_ON_ONCE(access_weight < 1)) + return 0; + + return layer + << ((access_weight - 1) * HWEIGHT(LANDLOCK_MAX_NUM_LAYERS - 1)); +} + +#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST + +static void test_get_layer_deny_mask(struct kunit *const test) +{ + const unsigned long truncate = BIT_INDEX(LANDLOCK_ACCESS_FS_TRUNCATE); + const unsigned long ioctl_dev = BIT_INDEX(LANDLOCK_ACCESS_FS_IOCTL_DEV); + + KUNIT_EXPECT_EQ(test, 0, + get_layer_deny_mask(_LANDLOCK_ACCESS_FS_OPTIONAL, + truncate, 0)); + KUNIT_EXPECT_EQ(test, 0x3, + get_layer_deny_mask(_LANDLOCK_ACCESS_FS_OPTIONAL, + truncate, 3)); + + KUNIT_EXPECT_EQ(test, 0, + get_layer_deny_mask(_LANDLOCK_ACCESS_FS_OPTIONAL, + ioctl_dev, 0)); + KUNIT_EXPECT_EQ(test, 0xf0, + get_layer_deny_mask(_LANDLOCK_ACCESS_FS_OPTIONAL, + ioctl_dev, 15)); +} + +#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ + +deny_masks_t +landlock_get_deny_masks(const access_mask_t all_existing_optional_access, + const access_mask_t optional_access, + const layer_mask_t (*const layer_masks)[], + const size_t layer_masks_size) +{ + const unsigned long access_opt = optional_access; + unsigned long access_bit; + deny_masks_t deny_masks = 0; + + /* This may require change with new object types. */ + WARN_ON_ONCE(access_opt != + (optional_access & all_existing_optional_access)); + + if (WARN_ON_ONCE(!layer_masks)) + return 0; + + if (WARN_ON_ONCE(!access_opt)) + return 0; + + for_each_set_bit(access_bit, &access_opt, layer_masks_size) { + const layer_mask_t mask = (*layer_masks)[access_bit]; + + if (!mask) + continue; + + /* __fls(1) == 0 */ + deny_masks |= get_layer_deny_mask(all_existing_optional_access, + access_bit, __fls(mask)); + } + return deny_masks; +} + +#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST + +static void test_landlock_get_deny_masks(struct kunit *const test) +{ + const layer_mask_t layers1[BITS_PER_TYPE(access_mask_t)] = { + [BIT_INDEX(LANDLOCK_ACCESS_FS_EXECUTE)] = BIT_ULL(0) | + BIT_ULL(9), + [BIT_INDEX(LANDLOCK_ACCESS_FS_TRUNCATE)] = BIT_ULL(1), + [BIT_INDEX(LANDLOCK_ACCESS_FS_IOCTL_DEV)] = BIT_ULL(2) | + BIT_ULL(0), + }; + + KUNIT_EXPECT_EQ(test, 0x1, + landlock_get_deny_masks(_LANDLOCK_ACCESS_FS_OPTIONAL, + LANDLOCK_ACCESS_FS_TRUNCATE, + &layers1, ARRAY_SIZE(layers1))); + KUNIT_EXPECT_EQ(test, 0x20, + landlock_get_deny_masks(_LANDLOCK_ACCESS_FS_OPTIONAL, + LANDLOCK_ACCESS_FS_IOCTL_DEV, + &layers1, ARRAY_SIZE(layers1))); + KUNIT_EXPECT_EQ( + test, 0x21, + landlock_get_deny_masks(_LANDLOCK_ACCESS_FS_OPTIONAL, + LANDLOCK_ACCESS_FS_TRUNCATE | + LANDLOCK_ACCESS_FS_IOCTL_DEV, + &layers1, ARRAY_SIZE(layers1))); +} + +#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ + +#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST + +static struct kunit_case test_cases[] = { + /* clang-format off */ + KUNIT_CASE(test_get_layer_deny_mask), + KUNIT_CASE(test_landlock_get_deny_masks), + {} + /* clang-format on */ +}; + +static struct kunit_suite test_suite = { + .name = "landlock_domain", + .test_cases = test_cases, +}; + +kunit_test_suite(test_suite); + +#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */ + #endif /* CONFIG_AUDIT */ diff --git a/security/landlock/domain.h b/security/landlock/domain.h index a7fda9c6a5a3..e1129ab09a1b 100644 --- a/security/landlock/domain.h +++ b/security/landlock/domain.h @@ -18,6 +18,8 @@ #include <linux/sched.h> #include <linux/time64.h> +#include "access.h" + enum landlock_log_status { LANDLOCK_LOG_PENDING = 0, LANDLOCK_LOG_RECORDED, @@ -103,6 +105,12 @@ struct landlock_hierarchy { int landlock_init_current_hierarchy(struct landlock_hierarchy *const hierarchy); +deny_masks_t +landlock_get_deny_masks(const access_mask_t all_existing_optional_access, + const access_mask_t optional_access, + const layer_mask_t (*const layer_masks)[], + size_t layer_masks_size); + #else /* CONFIG_AUDIT */ static inline int diff --git a/security/landlock/fs.c b/security/landlock/fs.c index f38c7a60b9bf..6404961ecbc7 100644 --- a/security/landlock/fs.c +++ b/security/landlock/fs.c @@ -246,6 +246,17 @@ is_masked_device_ioctl_compat(const unsigned int cmd) } } +static void +update_request(struct landlock_request *const request, + const struct landlock_file_security *const file_security, + const access_mask_t access) +{ + request->access = access; +#ifdef CONFIG_AUDIT + request->deny_masks = file_security->deny_masks; +#endif /* CONFIG_AUDIT */ +} + /* Ruleset management */ static struct landlock_object *get_inode_object(struct inode *const inode) @@ -1653,6 +1664,11 @@ static int hook_file_open(struct file *const file) * file access rights in the opened struct file. */ landlock_file(file)->allowed_access = allowed_access; +#ifdef CONFIG_AUDIT + landlock_file(file)->deny_masks = landlock_get_deny_masks( + _LANDLOCK_ACCESS_FS_OPTIONAL, optional_access, &layer_masks, + ARRAY_SIZE(layer_masks)); +#endif /* CONFIG_AUDIT */ if ((open_access_request & allowed_access) == open_access_request) return 0; @@ -1665,6 +1681,15 @@ static int hook_file_open(struct file *const file) static int hook_file_truncate(struct file *const file) { + struct landlock_request request = { + .type = LANDLOCK_REQUEST_FS_ACCESS, + .audit = { + .type = LSM_AUDIT_DATA_FILE, + .u.file = file, + }, + .all_existing_optional_access = _LANDLOCK_ACCESS_FS_OPTIONAL, + }; + /* * Allows truncation if the truncate right was available at the time of * opening the file, to get a consistent access check as for read, write @@ -1677,12 +1702,24 @@ static int hook_file_truncate(struct file *const file) */ if (landlock_file(file)->allowed_access & LANDLOCK_ACCESS_FS_TRUNCATE) return 0; + + update_request(&request, landlock_file(file), + LANDLOCK_ACCESS_FS_TRUNCATE); + landlock_log_denial(landlock_cred(file->f_cred)->domain, &request); return -EACCES; } static int hook_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { + struct landlock_request request = { + .type = LANDLOCK_REQUEST_FS_ACCESS, + .audit = { + .type = LSM_AUDIT_DATA_FILE, + .u.file = file, + }, + .all_existing_optional_access = _LANDLOCK_ACCESS_FS_OPTIONAL, + }; access_mask_t allowed_access = landlock_file(file)->allowed_access; /* @@ -1700,12 +1737,23 @@ static int hook_file_ioctl(struct file *file, unsigned int cmd, if (is_masked_device_ioctl(cmd)) return 0; + update_request(&request, landlock_file(file), + LANDLOCK_ACCESS_FS_IOCTL_DEV); + landlock_log_denial(landlock_cred(file->f_cred)->domain, &request); return -EACCES; } static int hook_file_ioctl_compat(struct file *file, unsigned int cmd, unsigned long arg) { + struct landlock_request request = { + .type = LANDLOCK_REQUEST_FS_ACCESS, + .audit = { + .type = LSM_AUDIT_DATA_FILE, + .u.file = file, + }, + .all_existing_optional_access = _LANDLOCK_ACCESS_FS_OPTIONAL, + }; access_mask_t allowed_access = landlock_file(file)->allowed_access; /* @@ -1723,6 +1771,9 @@ static int hook_file_ioctl_compat(struct file *file, unsigned int cmd, if (is_masked_device_ioctl_compat(cmd)) return 0; + update_request(&request, landlock_file(file), + LANDLOCK_ACCESS_FS_IOCTL_DEV); + landlock_log_denial(landlock_cred(file->f_cred)->domain, &request); return -EACCES; } diff --git a/security/landlock/fs.h b/security/landlock/fs.h index d445f411c26a..9f52c9b37898 100644 --- a/security/landlock/fs.h +++ b/security/landlock/fs.h @@ -53,6 +53,15 @@ struct landlock_file_security { * needed to authorize later operations on the open file. */ access_mask_t allowed_access; + +#ifdef CONFIG_AUDIT + /** + * @deny_masks: Domain layer levels that deny an optional access (see + * _LANDLOCK_ACCESS_FS_OPTIONAL). + */ + deny_masks_t deny_masks; +#endif /* CONFIG_AUDIT */ + /** * @fown_domain: Domain of the task that set the PID that may receive a * signal e.g., SIGURG when writing MSG_OOB to the related socket. -- 2.47.1
