[RFC PATCH v1 04/11] landlock: Wrap per-layer access masks in struct layer_rights

Mickaël Salaün
2026-03-12T10:13:58Z

The per-layer FAM in struct landlock_ruleset currently stores struct
access_masks directly, but upcoming permission features (capability
and namespace restrictions) need additional per-layer data beyond the
handled-access bitfields.

Introduce struct layer_rights as a wrapper around struct access_masks
and rename the FAM from access_masks[] to layers[]. This makes room
for future per-layer fields (e.g. allowed bitmasks) without modifying
struct access_masks itself, which is also used as a lightweight
parameter type for functions that only need the handled-access
bitfields.

No functional change.

Cc: Günther Noack <gnoack@google.com>
Signed-off-by: Mickaël Salaün <mic@digikod.net>
---
security/landlock/access.h | 29 ++++++++++++++++++++++-------
security/landlock/cred.h | 2 +-
security/landlock/ruleset.c | 12 ++++++------
security/landlock/ruleset.h | 28 +++++++++++++++-------------
security/landlock/syscalls.c | 2 +-
5 files changed, 45 insertions(+), 28 deletions(-)

diff --git a/security/landlock/access.h b/security/landlock/access.h
index 42c95747d7bd..b3e147771a0e 100644
--- a/security/landlock/access.h
+++ b/security/landlock/access.h
@@ -19,7 +19,7 @@

/*
* All access rights that are denied by default whether they are handled or not
- * by a ruleset/layer. This must be ORed with all ruleset->access_masks[]
+ * by a ruleset/layer. This must be ORed with all ruleset->layers[]
* entries when we need to get the absolute handled access masks, see
* landlock_upgrade_handled_access_masks().
*/
@@ -45,7 +45,7 @@ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_SCOPE);
/* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */
static_assert(sizeof(unsigned long) >= sizeof(access_mask_t));

-/* Ruleset access masks. */
+/* Handled access masks (bitfields only). */
struct access_masks {
access_mask_t fs : LANDLOCK_NUM_ACCESS_FS;
access_mask_t net : LANDLOCK_NUM_ACCESS_NET;
@@ -61,6 +61,21 @@ union access_masks_all {
static_assert(sizeof(typeof_member(union access_masks_all, masks)) ==
sizeof(typeof_member(union access_masks_all, all)));

+/**
+ * struct layer_rights - Per-layer access configuration
+ *
+ * Wraps the handled-access bitfields together with any additional per-layer
+ * data (e.g. allowed bitmasks added by future patches). This is the element
+ * type of the &struct landlock_ruleset.layers FAM.
+ */
+struct layer_rights {
+ /**
+ * @handled: Bitmask of access rights handled (i.e. restricted) by
+ * this layer.
+ */
+ struct access_masks handled;
+};
+
/**
* struct layer_access_masks - A boolean matrix of layers and access rights
*
@@ -100,17 +115,17 @@ static_assert(BITS_PER_TYPE(deny_masks_t) >=
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)
+static inline struct layer_rights
+landlock_upgrade_handled_access_masks(struct layer_rights layer_rights)
{
/*
* All access rights that are denied by default whether they are
* explicitly handled or not.
*/
- if (access_masks.fs)
- access_masks.fs |= _LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
+ if (layer_rights.handled.fs)
+ layer_rights.handled.fs |= _LANDLOCK_ACCESS_FS_INITIALLY_DENIED;

- return access_masks;
+ return layer_rights;
}

/* Checks the subset relation between access masks. */
diff --git a/security/landlock/cred.h b/security/landlock/cred.h
index f287c56b5fd4..3e2a7e88710e 100644
--- a/security/landlock/cred.h
+++ b/security/landlock/cred.h
@@ -139,7 +139,7 @@ landlock_get_applicable_subject(const struct cred *const cred,
for (layer_level = domain->num_layers - 1; layer_level >= 0;
layer_level--) {
union access_masks_all layer = {
- .masks = domain->access_masks[layer_level],
+ .masks = domain->layers[layer_level].handled,
};

if (layer.all & masks_all.all) {
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 181df7736bb9..a7f8be37ec31 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -32,7 +32,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
{
struct landlock_ruleset *new_ruleset;

- new_ruleset = kzalloc_flex(*new_ruleset, access_masks, num_layers,
+ new_ruleset = kzalloc_flex(*new_ruleset, layers, num_layers,
GFP_KERNEL_ACCOUNT);
if (!new_ruleset)
return ERR_PTR(-ENOMEM);
@@ -48,7 +48,7 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers)
/*
* hierarchy = NULL
* num_rules = 0
- * access_masks[] = 0
+ * layers[] = 0
*/
return new_ruleset;
}
@@ -381,8 +381,8 @@ static int merge_ruleset(struct landlock_ruleset *const dst,
err = -EINVAL;
goto out_unlock;
}
- dst->access_masks[dst->num_layers - 1] =
- landlock_upgrade_handled_access_masks(src->access_masks[0]);
+ dst->layers[dst->num_layers - 1] =
+ landlock_upgrade_handled_access_masks(src->layers[0]);

/* Merges the @src inode tree. */
err = merge_tree(dst, src, LANDLOCK_KEY_INODE);
@@ -464,8 +464,8 @@ static int inherit_ruleset(struct landlock_ruleset *const parent,
goto out_unlock;
}
/* Copies the parent layer stack and leaves a space for the new layer. */
- memcpy(child->access_masks, parent->access_masks,
- flex_array_size(parent, access_masks, parent->num_layers));
+ memcpy(child->layers, parent->layers,
+ flex_array_size(parent, layers, parent->num_layers));

if (WARN_ON_ONCE(!parent->hierarchy)) {
err = -EINVAL;
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 889f4b30301a..900c47eb0216 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -146,7 +146,7 @@ struct landlock_ruleset {
* section. This is only used by
* landlock_put_ruleset_deferred() when @usage reaches zero.
* The fields @lock, @usage, @num_rules, @num_layers and
- * @access_masks are then unused.
+ * @layers are then unused.
*/
struct work_struct work_free;
struct {
@@ -173,9 +173,10 @@ struct landlock_ruleset {
*/
u32 num_layers;
/**
- * @access_masks: Contains the subset of filesystem and
- * network actions that are restricted by a ruleset.
- * A domain saves all layers of merged rulesets in a
+ * @layers: Per-layer access configuration, including
+ * handled access masks and allowed permission
+ * bitmasks. A domain saves all layers of merged
+ * rulesets in a
* stack (FAM), starting from the first layer to the
* last one. These layers are used when merging
* rulesets, for user space backward compatibility
@@ -184,7 +185,7 @@ struct landlock_ruleset {
* layers are set once and never changed for the
* lifetime of the ruleset.
*/
- struct access_masks access_masks[];
+ struct layer_rights layers[] __counted_by(num_layers);
};
};
};
@@ -224,7 +225,8 @@ static inline void landlock_get_ruleset(struct landlock_ruleset *const ruleset)
*
* @domain: Landlock ruleset (used as a domain)
*
- * Return: An access_masks result of the OR of all the domain's access masks.
+ * Return: An access_masks result of the OR of all the domain's handled access
+ * masks.
*/
static inline struct access_masks
landlock_union_access_masks(const struct landlock_ruleset *const domain)
@@ -234,7 +236,7 @@ landlock_union_access_masks(const struct landlock_ruleset *const domain)

for (layer_level = 0; layer_level < domain->num_layers; layer_level++) {
union access_masks_all layer = {
- .masks = domain->access_masks[layer_level],
+ .masks = domain->layers[layer_level].handled,
};

matches.all |= layer.all;
@@ -252,7 +254,7 @@ landlock_add_fs_access_mask(struct landlock_ruleset *const ruleset,

/* Should already be checked in sys_landlock_create_ruleset(). */
WARN_ON_ONCE(fs_access_mask != fs_mask);
- ruleset->access_masks[layer_level].fs |= fs_mask;
+ ruleset->layers[layer_level].handled.fs |= fs_mask;
}

static inline void
@@ -264,7 +266,7 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset,

/* Should already be checked in sys_landlock_create_ruleset(). */
WARN_ON_ONCE(net_access_mask != net_mask);
- ruleset->access_masks[layer_level].net |= net_mask;
+ ruleset->layers[layer_level].handled.net |= net_mask;
}

static inline void
@@ -275,7 +277,7 @@ landlock_add_scope_mask(struct landlock_ruleset *const ruleset,

/* Should already be checked in sys_landlock_create_ruleset(). */
WARN_ON_ONCE(scope_mask != mask);
- ruleset->access_masks[layer_level].scope |= mask;
+ ruleset->layers[layer_level].handled.scope |= mask;
}

static inline access_mask_t
@@ -283,7 +285,7 @@ landlock_get_fs_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
/* Handles all initially denied by default access rights. */
- return ruleset->access_masks[layer_level].fs |
+ return ruleset->layers[layer_level].handled.fs |
_LANDLOCK_ACCESS_FS_INITIALLY_DENIED;
}

@@ -291,14 +293,14 @@ static inline access_mask_t
landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
- return ruleset->access_masks[layer_level].net;
+ return ruleset->layers[layer_level].handled.net;
}

static inline access_mask_t
landlock_get_scope_mask(const struct landlock_ruleset *const ruleset,
const u16 layer_level)
{
- return ruleset->access_masks[layer_level].scope;
+ return ruleset->layers[layer_level].handled.scope;
}

bool landlock_unmask_layers(const struct landlock_rule *const rule,
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index 3b33839b80c7..2aa7b50d875f 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -341,7 +341,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
return -ENOMSG;

/* Checks that allowed_access matches the @ruleset constraints. */
- mask = ruleset->access_masks[0].fs;
+ mask = ruleset->layers[0].handled.fs;
if ((path_beneath_attr.allowed_access | mask) != mask)
return -EINVAL;

--
2.53.0