[PATCH v4 0/5] Implement LANDLOCK_ADD_RULE_NO_INHERIT

[PATCH v4 0/5] Implement LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess]

Hi,

This is version 4 of the LANDLOCK_ADD_RULE_NO_INHERIT series, which
implements a new flag to suppress inheritance of access rights and
flags from parent objects.

This series is rebased on v6 of Tingmao Wang's "quiet flag" series.

The new flag enables policies where a parent directory needs broader
access than its children. For example, a sandbox may permit read-write
access to /home/user but still prohibit writes to ~/.bashrc or
~/.ssh, even though they are nested beneath the parent. Today this is
not possible because access rights always propagate from parent to
child within a layer.

When a rule is added with LANDLOCK_ADD_RULE_NO_INHERIT:

  * access rights on parent inodes are ignored for that inode and its
    descendants; and
  * operations that change the filesystem ancestors of such objects
    (via rename, rmdir, link) are denied up to the VFS root
    (new in v4); and
  * parent flags do not propagate below a NO_INHERIT rule.

These parent-directory restrictions help mitigate sandbox-restart
attacks: a sandboxed process could otherwise move a protected
directory before exit, causing the next sandbox instance to apply its
policy to the wrong path.

Changes since v3:

  1. Trimmed core implementation in fs.c by removing redundant functions.
  2. Fixed placement/inclusion of prototypes.
  3. Added 4 new selftests for bind mount cases.
  4. Protections now apply up to the VFS root instead of the mountpoint
     root.

Changes since v2:

  1. Add six new selftests for the new flag.
  2. Add an optimization to stop permission harvesting when all
     relevant layers are tagged with NO_INHERIT.
  3. Suppress inheritance of parent flags.
  4. Rebase onto v5 of the quiet-flag series.
  5. Remove the xarray structure used for flag tracking in favor of
     blank rule insertion, simplifying the implementation.
  6. Fix edge cases involving flag inheritance across multiple
     NO_INHERIT layers.
  7. Add documenting comments to new functions.

Links:

v1:
  https://lore.kernel.org/linux-security-module/20251105180019.1432367-1-utilityemal77@gmail.com/T/#t
v2:
  https://lore.kernel.org/linux-security-module/20251120222346.1157004-1-utilityemal77@gmail.com/T/#t
v3:
  https://lore.kernel.org/linux-security-module/20251126122039.3832162-1-utilityemal77@gmail.com/
quiet-flag v6:
  https://lore.kernel.org/linux-security-module/cover.1765040503.git.m@maowtm.org/

Example usage:

  # LL_FS_RO="/a/b/c" LL_FS_RW="/" LL_FS_NO_INHERIT="/a/b/c"
    landlock-sandboxer sh
  # touch /a/b/c/fi                    # denied; / RW does not inherit
  # rmdir /a/b/c                       # denied by ancestor protections
  # mv /a /bad                         # denied
  # mkdir /a/good; touch /a/good/fi    # allowed; unrelated path

Again, if preferred, I'm happy to split the selftests into multiple
commits.

This version simplifies a lot of the code in the core implementation.
Special thanks to Tingmao Wang for your valuable feedback.

Thank you for your time and review.

Regards,
Justin Suess

Justin Suess (5):
  landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT
  landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT userspace api
  samples/landlock: Add LANDLOCK_ADD_RULE_NO_INHERIT to
    landlock-sandboxer
  selftests/landlock: Implement selftests for
    LANDLOCK_ADD_RULE_NO_INHERIT
  landlock: Implement KUnit test for LANDLOCK_ADD_RULE_NO_INHERIT

 include/uapi/linux/landlock.h              |  29 +
 samples/landlock/sandboxer.c               |  13 +-
 security/landlock/fs.c                     | 389 ++++++++++-
 security/landlock/ruleset.c                | 108 +++-
 security/landlock/ruleset.h                |  29 +-
 security/landlock/syscalls.c               |  16 +-
 tools/testing/selftests/landlock/fs_test.c | 710 +++++++++++++++++++++
 7 files changed, 1285 insertions(+), 9 deletions(-)


base-commit: 92f98eb2cc08c6e2d093d4682f1cd1204728e97e
-- 
2.51.0

[PATCH v4 1/5] landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess]

Implements a flag to prevent access grant inheritance within the filesystem
hierarchy for landlock rules.

If a landlock rule on an inode has this flag, any access grants on parent
inodes will be ignored. Moreover, operations that involve altering the
ancestors of the subject with LANDLOCK_ADD_RULE_NO_INHERIT will be
denied up to the VFS root (new in v4).

For example, if /a/b/c/ = read only + LANDLOCK_ADD_RULE_NO_INHERIT and
/ = read write, writes to files in /a/b/c will be denied. Moreover,
moving /a to /bad, removing /a/b/c, or creating links to /a will be
prohibited.

Parent flag inheritance is automatically suppressed by the permission
harvesting logic, which will finish processing early if all relevant
layers are tagged with NO_INHERIT.

And if / has LANDLOCK_ADD_RULE_QUIET, /a/b/c will still audit (handled)
accesses. This is because LANDLOCK_ADD_RULE_NO_INHERIT also
suppresses flag inheritance from parent objects.

The parent directory restrictions mitigate sandbox-restart attacks. For
example, if a sandboxed program is able to move a
LANDLOCK_ADD_RULE_NO_INHERIT restricted directory, upon sandbox restart,
the policy applied naively on the same filenames would be invalid.
Preventing these operations mitigates these attacks.

v3..v4 changes:

  * Rebased on v6 of Tingmao Wang's "quiet flag" series.
  * Removed unnecessary mask_no_inherit_descendant_layers and related
    code at Tingmao Wang's suggestion, simplifying patch.
  * Updated to use new disconnected directory handling.
  * Improved WARN_ON_ONCE usage. (Thanks Tingmao Wang!)
  * Removed redundant loop for single-layer rulesets (again thanks Tingmao
    Wang!)
  * Protections now apply up to the VFS root, not just the mountpoint.
  * Indentation fixes.
  * Removed redundant flag marker blocked_flag_masks.

v2..v3 changes:

  * Parent directory topology protections now work by lazily
    inserting blank rules on parent inodes if they do not
    exist. This replaces the previous xarray implementation
    with simplified logic.
  * Added an optimization to skip further processing if all layers
    collected have no inherit.
  * Added support to block flag inheritance.

Cc: Tingmao Wang <m@maowtm.org>
Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 security/landlock/fs.c      | 389 +++++++++++++++++++++++++++++++++++-
 security/landlock/ruleset.c |  19 +-
 security/landlock/ruleset.h |  29 ++-
 3 files changed, 433 insertions(+), 4 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 0b589263ea42..7b0b77859778 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -317,6 +317,207 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
 	LANDLOCK_ACCESS_FS_IOCTL_DEV)
 /* clang-format on */
 
+static const struct landlock_rule *find_rule(const struct landlock_ruleset *const domain,
+					     const struct dentry *const dentry);
+
+/**
+ * landlock_domain_layers_mask - Build a mask covering all layers of a domain
+ * @domain: The ruleset (domain) to inspect.
+ *
+ * Return a layer mask with a 1 bit for each existing layer of @domain.
+ * If @domain has no layers 0 is returned.  If the number of layers is
+ * greater than or equal to the number of bits in layer_mask_t, all bits
+ * are set.
+ */
+static layer_mask_t landlock_domain_layers_mask(const struct landlock_ruleset
+						*const domain)
+{
+	if (!domain || !domain->num_layers)
+		return 0;
+
+	if (domain->num_layers >= sizeof(layer_mask_t) * BITS_PER_BYTE)
+		return (layer_mask_t)~0ULL;
+
+	return GENMASK_ULL(domain->num_layers - 1, 0);
+}
+
+/**
+ * rule_blocks_all_layers_no_inherit - check whether a rule disables inheritance
+ * @domain_layers_mask: Mask describing the domain's active layers.
+ * @rule: Rule to inspect.
+ *
+ * Return true if every layer present in @rule has its no_inherit flag set
+ * and the set of layers covered by the rule equals @domain_layers_mask.
+ * This indicates that the rule prevents inheritance on all layers of the
+ * domain and thus further walking for inheritance checks can stop.
+ */
+static bool rule_blocks_all_layers_no_inherit(const layer_mask_t domain_layers_mask,
+					      const struct landlock_rule *const rule)
+{
+	layer_mask_t rule_layers = 0;
+	u32 layer_index;
+
+	if (!domain_layers_mask || !rule)
+		return false;
+
+	for (layer_index = 0; layer_index < rule->num_layers; layer_index++) {
+		const struct landlock_layer *const layer =
+			&rule->layers[layer_index];
+		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
+
+		if (!layer->flags.no_inherit)
+			return false;
+
+		rule_layers |= layer_bit;
+	}
+
+	return rule_layers && rule_layers == domain_layers_mask;
+}
+
+/**
+ * ensure_rule_for_dentry - ensure a ruleset contains a rule entry for dentry,
+ * inserting a blank rule if needed.
+ * @ruleset: Ruleset to modify/inspect.  Caller must hold @ruleset->lock.
+ * @dentry: Dentry to ensure a rule exists for.
+ *
+ * If no rule is currently associated with @dentry, insert an empty rule
+ * (with zero access) tied to the backing inode.  Returns a pointer to the
+ * rule associated with @dentry on success, NULL when @dentry is negative, or
+ * an ERR_PTR()-encoded error if the rule cannot be created.
+ *
+ * This is useful for LANDLOCK_ADD_RULE_NO_INHERIT processing, where a rule
+ * may need to be created for an ancestor dentry that does not yet have one
+ * to properly track no_inherit flags.
+ *
+ * The flags are set to zero if a rule is newly created, and the caller
+ * is responsible for setting them appropriately.
+ *
+ * The returned rule pointer's lifetime is tied to @ruleset.
+ */
+static const struct landlock_rule *
+ensure_rule_for_dentry(struct landlock_ruleset *const ruleset,
+		       struct dentry *const dentry)
+{
+	struct landlock_id id = {
+		.type = LANDLOCK_KEY_INODE,
+	};
+	const struct landlock_rule *rule;
+	int err;
+
+	if (WARN_ON_ONCE(!ruleset || !dentry || d_is_negative(dentry)))
+		return NULL;
+
+	lockdep_assert_held(&ruleset->lock);
+
+	rule = find_rule(ruleset, dentry);
+	if (rule)
+		return rule;
+
+	id.key.object = get_inode_object(d_backing_inode(dentry));
+	if (IS_ERR(id.key.object))
+		return ERR_CAST(id.key.object);
+
+	err = landlock_insert_rule(ruleset, id, 0, 0);
+	landlock_put_object(id.key.object);
+	if (err)
+		return ERR_PTR(err);
+
+	rule = find_rule(ruleset, dentry);
+	if (WARN_ON_ONCE(!rule))
+		return ERR_PTR(-ENOENT);
+	return rule;
+}
+
+/**
+ * mark_no_inherit_ancestors - mark ancestors as having no_inherit descendants
+ * @ruleset: Ruleset to modify.  Caller must hold @ruleset->lock.
+ * @path: Path representing the descendant that carries no_inherit bits.
+ * @descendant_layers: Mask of layers from the descendant that should be
+ *                     advertised to ancestors via has_no_inherit_descendant.
+ *
+ * Walks upward from @dentry and ensures that any ancestor rule contains the
+ * has_no_inherit_descendant marker for the specified @descendant_layers so
+ * parent lookups can quickly detect descendant no_inherit influence.
+ *
+ * Returns 0 on success or a negative errno if ancestor bookkeeping fails.
+ */
+static int mark_no_inherit_ancestors(struct landlock_ruleset *ruleset,
+				     const struct path *const path,
+				     layer_mask_t descendant_layers)
+{
+	struct dentry *cursor;
+	struct path walk_path;
+	int err = 0;
+
+	if (WARN_ON_ONCE(!ruleset || !path || !path->dentry || !path->mnt ||
+			 !descendant_layers))
+		return -EINVAL;
+
+	lockdep_assert_held(&ruleset->lock);
+
+	walk_path.mnt = path->mnt;
+	walk_path.dentry = path->dentry;
+	path_get(&walk_path);
+
+	cursor = dget(walk_path.dentry);
+	while (cursor) {
+		struct dentry *parent;
+		const struct landlock_rule *rule;
+
+		/* Follow mounts all the way up to the root. */
+		if (IS_ROOT(cursor)) {
+			dput(cursor);
+			if (!follow_up(&walk_path)) {
+				cursor = NULL;
+				continue;
+			}
+			cursor = dget(walk_path.dentry);
+		}
+
+		parent = dget_parent(cursor);
+		dput(cursor);
+		if (!parent)
+			break;
+
+		if (WARN_ON_ONCE(d_is_negative(parent))) {
+			dput(parent);
+			break;
+		}
+		/*
+		 * Ensures a rule exists for the parent dentry,
+		 * inserting a blank one if needed.
+		 */
+		rule = ensure_rule_for_dentry(ruleset, parent);
+		if (IS_ERR(rule)) {
+			err = PTR_ERR(rule);
+			dput(parent);
+			cursor = NULL;
+			break;
+		}
+		if (rule) {
+			struct landlock_rule *mutable_rule =
+				(struct landlock_rule *)rule;
+			/*
+			 * Unmerged rulesets should only have one layer.
+			 */
+			if (WARN_ON_ONCE(mutable_rule->num_layers != 1)) {
+				dput(parent);
+				err = -EINVAL;
+				cursor = NULL;
+				break;
+			}
+
+			if (descendant_layers & BIT_ULL(0))
+				mutable_rule->layers[0]
+					.flags.has_no_inherit_descendant = true;
+		}
+
+		cursor = parent;
+	}
+	path_put(&walk_path);
+	return err;
+}
+
 /*
  * @path: Should have been checked by get_path_from_fd().
  */
@@ -344,13 +545,40 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
 		return PTR_ERR(id.key.object);
 	mutex_lock(&ruleset->lock);
 	err = landlock_insert_rule(ruleset, id, access_rights, flags);
+	if (!err && (flags & LANDLOCK_ADD_RULE_NO_INHERIT)) {
+		const struct landlock_rule *rule;
+		layer_mask_t descendant_layers = 0;
+
+		rule = find_rule(ruleset, path->dentry);
+		/*
+		 * This was already checked at function entry.
+		 */
+		if (WARN_ON_ONCE(!rule || rule->num_layers != 1))
+			goto out_unlock;
+
+		if (rule->layers[0].flags.no_inherit ||
+		    rule->layers[0].flags.has_no_inherit_descendant)
+			descendant_layers = BIT_ULL(0);
+
+		if (descendant_layers) {
+			err = mark_no_inherit_ancestors(ruleset, path,
+							descendant_layers);
+			if (err)
+				goto out_unlock;
+		}
+	}
 	mutex_unlock(&ruleset->lock);
+out:
 	/*
 	 * No need to check for an error because landlock_insert_rule()
 	 * increments the refcount for the new object if needed.
 	 */
 	landlock_put_object(id.key.object);
 	return err;
+
+out_unlock:
+	mutex_unlock(&ruleset->lock);
+	goto out;
 }
 
 /* Access-control management */
@@ -764,6 +992,8 @@ static bool is_access_to_paths_allowed(
 	struct landlock_request *const log_request_parent2,
 	struct dentry *const dentry_child2)
 {
+	const layer_mask_t domain_layers_mask =
+		landlock_domain_layers_mask(domain);
 	bool allowed_parent1 = false, allowed_parent2 = false, is_dom_check,
 	     child1_is_directory = true, child2_is_directory = true;
 	struct path walker_path;
@@ -906,6 +1136,10 @@ static bool is_access_to_paths_allowed(
 					       ARRAY_SIZE(*layer_masks_parent2),
 					       rule_flags_parent2);
 
+		if (rule &&
+		    rule_blocks_all_layers_no_inherit(domain_layers_mask, rule))
+			break;
+
 		/* Stops when a rule from each layer grants access. */
 		if (allowed_parent1 && allowed_parent2)
 			break;
@@ -1064,7 +1298,9 @@ static bool collect_domain_accesses(
 	layer_mask_t (*const layer_masks_dom)[LANDLOCK_NUM_ACCESS_FS],
 	struct collected_rule_flags *const rule_flags)
 {
-	unsigned long access_dom;
+	access_mask_t access_dom;
+	const layer_mask_t domain_layers_mask =
+		landlock_domain_layers_mask(domain);
 	bool ret = false;
 
 	if (WARN_ON_ONCE(!domain || !mnt_root || !dir || !layer_masks_dom))
@@ -1080,9 +1316,11 @@ static bool collect_domain_accesses(
 	while (true) {
 		struct dentry *parent_dentry;
 
+		const struct landlock_rule *rule = find_rule(domain, dir);
+
 		/* Gets all layers allowing all domain accesses. */
 		if (landlock_unmask_layers(
-			    find_rule(domain, dir), access_dom, layer_masks_dom,
+			    rule, access_dom, layer_masks_dom,
 			    ARRAY_SIZE(*layer_masks_dom), rule_flags)) {
 			/*
 			 * Stops when all handled accesses are allowed by at
@@ -1092,6 +1330,10 @@ static bool collect_domain_accesses(
 			break;
 		}
 
+		if (rule &&
+		    rule_blocks_all_layers_no_inherit(domain_layers_mask, rule))
+			break;
+
 		/*
 		 * Stops at the mount point or the filesystem root for a disconnected
 		 * directory.
@@ -1107,6 +1349,120 @@ static bool collect_domain_accesses(
 	return ret;
 }
 
+/**
+ * collect_topology_sealed_layers - collect layers sealed against topology changes
+ * @domain: Ruleset to consult.
+ * @dentry: Starting dentry for the upward walk.
+ * @override_layers: Optional out parameter filled with layers that are
+ *                   present on ancestors but considered overrides (not
+ *                   sealing the topology for descendants).
+ *
+ * Walk upwards from @dentry and return a mask of layers where either the
+ * visited dentry contains a no_inherit rule or ancestors were previously
+ * marked as having a descendant with no_inherit.  @override_layers, if not
+ * NULL, is filled with layers that would normally be overridden by more
+ * specific descendant rules.
+ *
+ * Returns a layer mask where set bits indicate layers that are "sealed"
+ * (topology changes like rename/rmdir are denied) for the subtree rooted at
+ * @dentry.
+ *
+ * Useful for LANDLOCK_ADD_RULE_NO_INHERIT parent directory enforcement to ensure
+ * that topology changes do not violate the no_inherit constraints.
+ */
+static layer_mask_t
+collect_topology_sealed_layers(const struct landlock_ruleset *const domain,
+			       struct dentry *dentry,
+			       layer_mask_t *const override_layers)
+{
+	struct dentry *cursor, *parent;
+	bool include_descendants = true;
+	layer_mask_t sealed_layers = 0;
+
+	if (override_layers)
+		*override_layers = 0;
+
+	if (WARN_ON_ONCE(!domain || !dentry || d_is_negative(dentry)))
+		return 0;
+
+	cursor = dget(dentry);
+	while (cursor) {
+		const struct landlock_rule *rule;
+		u32 layer_index;
+
+		rule = find_rule(domain, cursor);
+		if (rule) {
+			for (layer_index = 0; layer_index < rule->num_layers;
+			     layer_index++) {
+				const struct landlock_layer *layer =
+					&rule->layers[layer_index];
+				layer_mask_t layer_bit =
+					BIT_ULL(layer->level - 1);
+
+				if (include_descendants &&
+				    (layer->flags.no_inherit ||
+				     layer->flags.has_no_inherit_descendant)) {
+					sealed_layers |= layer_bit;
+				} else if (override_layers) {
+					*override_layers |= layer_bit;
+				}
+			}
+		}
+
+		if (sealed_layers || IS_ROOT(cursor))
+			break;
+
+		parent = dget_parent(cursor);
+		dput(cursor);
+		if (!parent)
+			return sealed_layers;
+
+		cursor = parent;
+		include_descendants = false;
+	}
+	dput(cursor);
+	return sealed_layers;
+}
+
+/**
+ * deny_no_inherit_topology_change - deny topology changes on sealed layers
+ * @subject: Subject performing the operation (contains the domain).
+ * @dentry: Dentry that is the target of the topology modification.
+ *
+ * Checks whether any domain layers are sealed against topology changes at
+ * @dentry (via collect_topology_sealed_layers).  If so, emit an audit record
+ * and return -EACCES.  Otherwise return 0.
+ */
+static int deny_no_inherit_topology_change(const struct landlock_cred_security
+					   *subject,
+					   struct dentry *dentry)
+{
+	layer_mask_t sealed_layers;
+	layer_mask_t override_layers;
+	unsigned long layer_index;
+
+	if (WARN_ON_ONCE(!subject || !dentry || d_is_negative(dentry)))
+		return 0;
+	sealed_layers = collect_topology_sealed_layers(subject->domain,
+						       dentry, &override_layers);
+	sealed_layers &= ~override_layers;
+
+	if (!sealed_layers)
+		return 0;
+
+	layer_index = __ffs((unsigned long)sealed_layers);
+	landlock_log_denial(subject, &(struct landlock_request) {
+		.type = LANDLOCK_REQUEST_FS_CHANGE_TOPOLOGY,
+		.audit = {
+			.type = LSM_AUDIT_DATA_DENTRY,
+			.u.dentry = dentry,
+		},
+		.layer_plus_one = layer_index + 1,
+	});
+
+	return -EACCES;
+}
+
 /**
  * current_check_refer_path - Check if a rename or link action is allowed
  *
@@ -1191,6 +1547,16 @@ static int current_check_refer_path(struct dentry *const old_dentry,
 	access_request_parent2 =
 		get_mode_access(d_backing_inode(old_dentry)->i_mode);
 	if (removable) {
+		int err;
+
+		err = deny_no_inherit_topology_change(subject, old_dentry);
+		if (err)
+			return err;
+		if (exchange) {
+			err = deny_no_inherit_topology_change(subject, new_dentry);
+			if (err)
+				return err;
+		}
 		access_request_parent1 |= maybe_remove(old_dentry);
 		access_request_parent2 |= maybe_remove(new_dentry);
 	}
@@ -1583,12 +1949,31 @@ static int hook_path_symlink(const struct path *const dir,
 static int hook_path_unlink(const struct path *const dir,
 			    struct dentry *const dentry)
 {
+	const struct landlock_cred_security *const subject =
+		landlock_get_applicable_subject(current_cred(), any_fs, NULL);
+	int err;
+
+	if (subject) {
+		err = deny_no_inherit_topology_change(subject, dentry);
+		if (err)
+			return err;
+	}
 	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_FILE);
 }
 
 static int hook_path_rmdir(const struct path *const dir,
 			   struct dentry *const dentry)
 {
+	const struct landlock_cred_security *const subject =
+		landlock_get_applicable_subject(current_cred(), any_fs, NULL);
+	int err;
+
+	if (subject) {
+		err = deny_no_inherit_topology_change(subject, dentry);
+		if (err)
+			return err;
+	}
+
 	return current_check_access_path(dir, LANDLOCK_ACCESS_FS_REMOVE_DIR);
 }
 
diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 750a444e1983..9152a939d79a 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -255,8 +255,13 @@ static int insert_rule(struct landlock_ruleset *const ruleset,
 				return -EINVAL;
 			if (WARN_ON_ONCE(this->layers[0].level != 0))
 				return -EINVAL;
+			/* Merge the flags into the rules */
 			this->layers[0].access |= (*layers)[0].access;
 			this->layers[0].flags.quiet |= (*layers)[0].flags.quiet;
+			this->layers[0].flags.no_inherit |=
+				(*layers)[0].flags.no_inherit;
+			this->layers[0].flags.has_no_inherit_descendant |=
+				(*layers)[0].flags.has_no_inherit_descendant;
 			return 0;
 		}
 
@@ -315,7 +320,10 @@ int landlock_insert_rule(struct landlock_ruleset *const ruleset,
 		.level = 0,
 		.flags = {
 			.quiet = !!(flags & LANDLOCK_ADD_RULE_QUIET),
-		},
+			.no_inherit = !!(flags & LANDLOCK_ADD_RULE_NO_INHERIT),
+			.has_no_inherit_descendant =
+				!!(flags & LANDLOCK_ADD_RULE_NO_INHERIT),
+		}
 	} };
 
 	build_check_layer();
@@ -662,9 +670,18 @@ bool landlock_unmask_layers(const struct landlock_rule *const rule,
 		unsigned long access_bit;
 		bool is_empty;
 
+		/* Skip layers that already have no inherit flags. */
+		if (rule_flags &&
+		    (rule_flags->no_inherit_masks & layer_bit))
+			continue;
+
 		/* Collect rule flags for each layer. */
 		if (rule_flags && layer->flags.quiet)
 			rule_flags->quiet_masks |= layer_bit;
+		if (rule_flags && layer->flags.no_inherit)
+			rule_flags->no_inherit_masks |= layer_bit;
+		if (rule_flags && layer->flags.has_no_inherit_descendant)
+			rule_flags->no_inherit_desc_masks |= layer_bit;
 
 		/*
 		 * Records in @layer_masks which layer grants access to each requested
diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index eb60db646422..81df6c56a152 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h
@@ -40,6 +40,21 @@ struct landlock_layer {
 		 * down the file hierarchy.
 		 */
 		bool quiet:1;
+		/**
+		 * @no_inherit: Prevents this rule from being inherited by
+		 * descendant directories in the filesystem layer.  Only used
+		 * for filesystem rules.
+		 */
+		bool no_inherit:1;
+		/**
+		 * @has_no_inherit_descendant: Marker to indicate that this layer
+		 * has at least one descendant directory with a rule having the
+		 * no_inherit flag.  Only used for filesystem rules.
+		 * This "flag" is not set by the user, but by Landlock on
+		 * parent directories of rules when the child rule has
+		 * a rule with the no_inherit flag.
+		 */
+		bool has_no_inherit_descendant:1;
 	} flags;
 	/**
 	 * @access: Bitfield of allowed actions on the kernel object.  They are
@@ -49,13 +64,25 @@ struct landlock_layer {
 };
 
 /**
- * struct collected_rule_flags - Hold accumulated flags for each layer.
+ * struct collected_rule_flags - Hold accumulated flags and their markers for each layer.
  */
 struct collected_rule_flags {
 	/**
 	 * @quiet_masks: Layers for which the quiet flag is effective.
 	 */
 	layer_mask_t quiet_masks;
+	/**
+	 * @no_inherit_masks: Layers for which the no_inherit flag is effective.
+	 */
+	layer_mask_t no_inherit_masks;
+	/**
+	 * @no_inherit_desc_masks: Layers for which the
+	 * has_no_inherit_descendant tag is effective.
+	 * This is not a flag itself, but a marker set on ancestors
+	 * of rules with the no_inherit flag to deny topology changes
+	 * in the direct parent path.
+	 */
+	layer_mask_t no_inherit_desc_masks;
 };
 
 /**
-- 
2.51.0

Re: [PATCH v4 1/5] landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT

[Mickaël Salaün]

Thanks for this patch series.  This feature would be useful, but the
related patches add a lot of new code.  We should try to minimize that
as much as possible, especially when similar/close logic already exist
(e.g. path walk).

On Sat, Dec 06, 2025 at 08:51:27PM -0500, Justin Suess wrote:
> Implements a flag to prevent access grant inheritance within the filesystem
> hierarchy for landlock rules.
> 
> If a landlock rule on an inode has this flag, any access grants on parent
> inodes will be ignored. Moreover, operations that involve altering the
> ancestors of the subject with LANDLOCK_ADD_RULE_NO_INHERIT will be
> denied up to the VFS root (new in v4).
> 
> For example, if /a/b/c/ = read only + LANDLOCK_ADD_RULE_NO_INHERIT and
> / = read write, writes to files in /a/b/c will be denied. Moreover,
> moving /a to /bad, removing /a/b/c, or creating links to /a will be
> prohibited.
> 
> Parent flag inheritance is automatically suppressed by the permission
> harvesting logic, which will finish processing early if all relevant
> layers are tagged with NO_INHERIT.
> 
> And if / has LANDLOCK_ADD_RULE_QUIET, /a/b/c will still audit (handled)
> accesses. This is because LANDLOCK_ADD_RULE_NO_INHERIT also
> suppresses flag inheritance from parent objects.
> 
> The parent directory restrictions mitigate sandbox-restart attacks. For
> example, if a sandboxed program is able to move a
> LANDLOCK_ADD_RULE_NO_INHERIT restricted directory, upon sandbox restart,
> the policy applied naively on the same filenames would be invalid.
> Preventing these operations mitigates these attacks.
> 

Your Signed-off-by and Cc should be here, followed by "---", followed by
the changelog (to exclude it from the git message e.g., when using
git am).

> v3..v4 changes:
> 
>   * Rebased on v6 of Tingmao Wang's "quiet flag" series.
>   * Removed unnecessary mask_no_inherit_descendant_layers and related
>     code at Tingmao Wang's suggestion, simplifying patch.
>   * Updated to use new disconnected directory handling.
>   * Improved WARN_ON_ONCE usage. (Thanks Tingmao Wang!)
>   * Removed redundant loop for single-layer rulesets (again thanks Tingmao
>     Wang!)
>   * Protections now apply up to the VFS root, not just the mountpoint.
>   * Indentation fixes.
>   * Removed redundant flag marker blocked_flag_masks.
> 
> v2..v3 changes:
> 
>   * Parent directory topology protections now work by lazily
>     inserting blank rules on parent inodes if they do not
>     exist. This replaces the previous xarray implementation
>     with simplified logic.
>   * Added an optimization to skip further processing if all layers
>     collected have no inherit.
>   * Added support to block flag inheritance.
> 
> Cc: Tingmao Wang <m@maowtm.org>
> Signed-off-by: Justin Suess <utilityemal77@gmail.com>
> ---
>  security/landlock/fs.c      | 389 +++++++++++++++++++++++++++++++++++-
>  security/landlock/ruleset.c |  19 +-
>  security/landlock/ruleset.h |  29 ++-
>  3 files changed, 433 insertions(+), 4 deletions(-)
> 
> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
> index 0b589263ea42..7b0b77859778 100644
> --- a/security/landlock/fs.c
> +++ b/security/landlock/fs.c
> @@ -317,6 +317,207 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
>  	LANDLOCK_ACCESS_FS_IOCTL_DEV)
>  /* clang-format on */
>  
> +static const struct landlock_rule *find_rule(const struct landlock_ruleset *const domain,
> +					     const struct dentry *const dentry);
> +
> +/**
> + * landlock_domain_layers_mask - Build a mask covering all layers of a domain
> + * @domain: The ruleset (domain) to inspect.
> + *
> + * Return a layer mask with a 1 bit for each existing layer of @domain.
> + * If @domain has no layers 0 is returned.  If the number of layers is
> + * greater than or equal to the number of bits in layer_mask_t, all bits
> + * are set.
> + */
> +static layer_mask_t landlock_domain_layers_mask(const struct landlock_ruleset
> +						*const domain)
> +{
> +	if (!domain || !domain->num_layers)
> +		return 0;
> +
> +	if (domain->num_layers >= sizeof(layer_mask_t) * BITS_PER_BYTE)
> +		return (layer_mask_t)~0ULL;
> +
> +	return GENMASK_ULL(domain->num_layers - 1, 0);
> +}
> +
> +/**
> + * rule_blocks_all_layers_no_inherit - check whether a rule disables inheritance
> + * @domain_layers_mask: Mask describing the domain's active layers.
> + * @rule: Rule to inspect.
> + *
> + * Return true if every layer present in @rule has its no_inherit flag set
> + * and the set of layers covered by the rule equals @domain_layers_mask.
> + * This indicates that the rule prevents inheritance on all layers of the
> + * domain and thus further walking for inheritance checks can stop.
> + */
> +static bool rule_blocks_all_layers_no_inherit(const layer_mask_t domain_layers_mask,
> +					      const struct landlock_rule *const rule)
> +{
> +	layer_mask_t rule_layers = 0;
> +	u32 layer_index;
> +
> +	if (!domain_layers_mask || !rule)
> +		return false;
> +
> +	for (layer_index = 0; layer_index < rule->num_layers; layer_index++) {
> +		const struct landlock_layer *const layer =
> +			&rule->layers[layer_index];
> +		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
> +
> +		if (!layer->flags.no_inherit)
> +			return false;
> +
> +		rule_layers |= layer_bit;
> +	}
> +
> +	return rule_layers && rule_layers == domain_layers_mask;
> +}
> +
> +/**
> + * ensure_rule_for_dentry - ensure a ruleset contains a rule entry for dentry,
> + * inserting a blank rule if needed.
> + * @ruleset: Ruleset to modify/inspect.  Caller must hold @ruleset->lock.
> + * @dentry: Dentry to ensure a rule exists for.
> + *
> + * If no rule is currently associated with @dentry, insert an empty rule
> + * (with zero access) tied to the backing inode.  Returns a pointer to the
> + * rule associated with @dentry on success, NULL when @dentry is negative, or
> + * an ERR_PTR()-encoded error if the rule cannot be created.
> + *
> + * This is useful for LANDLOCK_ADD_RULE_NO_INHERIT processing, where a rule
> + * may need to be created for an ancestor dentry that does not yet have one
> + * to properly track no_inherit flags.
> + *
> + * The flags are set to zero if a rule is newly created, and the caller
> + * is responsible for setting them appropriately.
> + *
> + * The returned rule pointer's lifetime is tied to @ruleset.
> + */
> +static const struct landlock_rule *
> +ensure_rule_for_dentry(struct landlock_ruleset *const ruleset,
> +		       struct dentry *const dentry)
> +{
> +	struct landlock_id id = {
> +		.type = LANDLOCK_KEY_INODE,
> +	};
> +	const struct landlock_rule *rule;
> +	int err;
> +
> +	if (WARN_ON_ONCE(!ruleset || !dentry || d_is_negative(dentry)))
> +		return NULL;
> +
> +	lockdep_assert_held(&ruleset->lock);
> +
> +	rule = find_rule(ruleset, dentry);
> +	if (rule)
> +		return rule;
> +
> +	id.key.object = get_inode_object(d_backing_inode(dentry));
> +	if (IS_ERR(id.key.object))
> +		return ERR_CAST(id.key.object);
> +
> +	err = landlock_insert_rule(ruleset, id, 0, 0);
> +	landlock_put_object(id.key.object);
> +	if (err)
> +		return ERR_PTR(err);
> +
> +	rule = find_rule(ruleset, dentry);
> +	if (WARN_ON_ONCE(!rule))
> +		return ERR_PTR(-ENOENT);
> +	return rule;
> +}
> +
> +/**
> + * mark_no_inherit_ancestors - mark ancestors as having no_inherit descendants
> + * @ruleset: Ruleset to modify.  Caller must hold @ruleset->lock.
> + * @path: Path representing the descendant that carries no_inherit bits.
> + * @descendant_layers: Mask of layers from the descendant that should be
> + *                     advertised to ancestors via has_no_inherit_descendant.
> + *
> + * Walks upward from @dentry and ensures that any ancestor rule contains the
> + * has_no_inherit_descendant marker for the specified @descendant_layers so
> + * parent lookups can quickly detect descendant no_inherit influence.
> + *
> + * Returns 0 on success or a negative errno if ancestor bookkeeping fails.
> + */
> +static int mark_no_inherit_ancestors(struct landlock_ruleset *ruleset,
> +				     const struct path *const path,
> +				     layer_mask_t descendant_layers)
> +{
> +	struct dentry *cursor;
> +	struct path walk_path;
> +	int err = 0;
> +
> +	if (WARN_ON_ONCE(!ruleset || !path || !path->dentry || !path->mnt ||
> +			 !descendant_layers))
> +		return -EINVAL;
> +
> +	lockdep_assert_held(&ruleset->lock);
> +
> +	walk_path.mnt = path->mnt;
> +	walk_path.dentry = path->dentry;
> +	path_get(&walk_path);
> +
> +	cursor = dget(walk_path.dentry);
> +	while (cursor) {
> +		struct dentry *parent;
> +		const struct landlock_rule *rule;
> +
> +		/* Follow mounts all the way up to the root. */
> +		if (IS_ROOT(cursor)) {
> +			dput(cursor);
> +			if (!follow_up(&walk_path)) {

This path walk is inconsistent and a duplicate of the (correct)
is_access_to_paths_allowed() one.  Please add a patch to factor out the
common parts as much as possible.  Ditto for the
collect_domain_accesses() and collect_topology_sealed_layers().

> +				cursor = NULL;
> +				continue;
> +			}
> +			cursor = dget(walk_path.dentry);
> +		}
> +
> +		parent = dget_parent(cursor);
> +		dput(cursor);
> +		if (!parent)
> +			break;
> +
> +		if (WARN_ON_ONCE(d_is_negative(parent))) {
> +			dput(parent);
> +			break;
> +		}
> +		/*
> +		 * Ensures a rule exists for the parent dentry,
> +		 * inserting a blank one if needed.
> +		 */
> +		rule = ensure_rule_for_dentry(ruleset, parent);
> +		if (IS_ERR(rule)) {
> +			err = PTR_ERR(rule);
> +			dput(parent);
> +			cursor = NULL;
> +			break;
> +		}
> +		if (rule) {
> +			struct landlock_rule *mutable_rule =
> +				(struct landlock_rule *)rule;
> +			/*
> +			 * Unmerged rulesets should only have one layer.
> +			 */
> +			if (WARN_ON_ONCE(mutable_rule->num_layers != 1)) {
> +				dput(parent);
> +				err = -EINVAL;
> +				cursor = NULL;
> +				break;
> +			}
> +
> +			if (descendant_layers & BIT_ULL(0))
> +				mutable_rule->layers[0]
> +					.flags.has_no_inherit_descendant = true;
> +		}
> +
> +		cursor = parent;
> +	}
> +	path_put(&walk_path);
> +	return err;
> +}

> +/**
> + * collect_topology_sealed_layers - collect layers sealed against topology changes
> + * @domain: Ruleset to consult.
> + * @dentry: Starting dentry for the upward walk.
> + * @override_layers: Optional out parameter filled with layers that are
> + *                   present on ancestors but considered overrides (not
> + *                   sealing the topology for descendants).
> + *
> + * Walk upwards from @dentry and return a mask of layers where either the
> + * visited dentry contains a no_inherit rule or ancestors were previously
> + * marked as having a descendant with no_inherit.  @override_layers, if not
> + * NULL, is filled with layers that would normally be overridden by more
> + * specific descendant rules.
> + *
> + * Returns a layer mask where set bits indicate layers that are "sealed"
> + * (topology changes like rename/rmdir are denied) for the subtree rooted at
> + * @dentry.
> + *
> + * Useful for LANDLOCK_ADD_RULE_NO_INHERIT parent directory enforcement to ensure
> + * that topology changes do not violate the no_inherit constraints.
> + */
> +static layer_mask_t
> +collect_topology_sealed_layers(const struct landlock_ruleset *const domain,
> +			       struct dentry *dentry,
> +			       layer_mask_t *const override_layers)
> +{
> +	struct dentry *cursor, *parent;
> +	bool include_descendants = true;
> +	layer_mask_t sealed_layers = 0;
> +
> +	if (override_layers)
> +		*override_layers = 0;
> +
> +	if (WARN_ON_ONCE(!domain || !dentry || d_is_negative(dentry)))
> +		return 0;
> +
> +	cursor = dget(dentry);
> +	while (cursor) {
> +		const struct landlock_rule *rule;
> +		u32 layer_index;
> +
> +		rule = find_rule(domain, cursor);
> +		if (rule) {
> +			for (layer_index = 0; layer_index < rule->num_layers;
> +			     layer_index++) {
> +				const struct landlock_layer *layer =
> +					&rule->layers[layer_index];
> +				layer_mask_t layer_bit =
> +					BIT_ULL(layer->level - 1);
> +
> +				if (include_descendants &&
> +				    (layer->flags.no_inherit ||
> +				     layer->flags.has_no_inherit_descendant)) {
> +					sealed_layers |= layer_bit;
> +				} else if (override_layers) {
> +					*override_layers |= layer_bit;
> +				}
> +			}
> +		}
> +
> +		if (sealed_layers || IS_ROOT(cursor))
> +			break;
> +
> +		parent = dget_parent(cursor);
> +		dput(cursor);
> +		if (!parent)
> +			return sealed_layers;
> +
> +		cursor = parent;
> +		include_descendants = false;
> +	}
> +	dput(cursor);
> +	return sealed_layers;
> +}

Re: [PATCH v4 1/5] landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess]

On 12/12/25 08:27, Mickaël Salaün wrote:
> Thanks for this patch series.  This feature would be useful, but the
> related patches add a lot of new code.  We should try to minimize that
> as much as possible, especially when similar/close logic already exist
> (e.g. path walk).

Agreed. I would like to get this patch much smaller. I'm glad you think the
feature is useful, it was a personal usecase that motivated me to make this
patch originally but I think having it would benefit a lot of downstream
projects.

I appreciate your patience and willingness to work with someone new to
kernel development and landlock. :)

> On Sat, Dec 06, 2025 at 08:51:27PM -0500, Justin Suess wrote:
>> Implements a flag to prevent access grant inheritance within the filesystem
>> hierarchy for landlock rules.
>>
>> If a landlock rule on an inode has this flag, any access grants on parent
>> inodes will be ignored. Moreover, operations that involve altering the
>> ancestors of the subject with LANDLOCK_ADD_RULE_NO_INHERIT will be
>> denied up to the VFS root (new in v4).
>>
>> For example, if /a/b/c/ = read only + LANDLOCK_ADD_RULE_NO_INHERIT and
>> / = read write, writes to files in /a/b/c will be denied. Moreover,
>> moving /a to /bad, removing /a/b/c, or creating links to /a will be
>> prohibited.
>>
>> Parent flag inheritance is automatically suppressed by the permission
>> harvesting logic, which will finish processing early if all relevant
>> layers are tagged with NO_INHERIT.
>>
>> And if / has LANDLOCK_ADD_RULE_QUIET, /a/b/c will still audit (handled)
>> accesses. This is because LANDLOCK_ADD_RULE_NO_INHERIT also
>> suppresses flag inheritance from parent objects.
>>
>> The parent directory restrictions mitigate sandbox-restart attacks. For
>> example, if a sandboxed program is able to move a
>> LANDLOCK_ADD_RULE_NO_INHERIT restricted directory, upon sandbox restart,
>> the policy applied naively on the same filenames would be invalid.
>> Preventing these operations mitigates these attacks.
>>
>
> Your Signed-off-by and Cc should be here, followed by "---", followed by
> the changelog (to exclude it from the git message e.g., when using
> git am).
>

Gotcha. I'll make sure to fix that.

>> v3..v4 changes:
>>
>>   * Rebased on v6 of Tingmao Wang's "quiet flag" series.
>>   * Removed unnecessary mask_no_inherit_descendant_layers and related
>>     code at Tingmao Wang's suggestion, simplifying patch.
>>   * Updated to use new disconnected directory handling.
>>   * Improved WARN_ON_ONCE usage. (Thanks Tingmao Wang!)
>>   * Removed redundant loop for single-layer rulesets (again thanks Tingmao
>>     Wang!)
>>   * Protections now apply up to the VFS root, not just the mountpoint.
>>   * Indentation fixes.
>>   * Removed redundant flag marker blocked_flag_masks.
>>
>> v2..v3 changes:
>>
>>   * Parent directory topology protections now work by lazily
>>     inserting blank rules on parent inodes if they do not
>>     exist. This replaces the previous xarray implementation
>>     with simplified logic.
>>   * Added an optimization to skip further processing if all layers
>>     collected have no inherit.
>>   * Added support to block flag inheritance.
>>
>> Cc: Tingmao Wang <m@maowtm.org>
>> Signed-off-by: Justin Suess <utilityemal77@gmail.com>
>> ---
>>  security/landlock/fs.c      | 389 +++++++++++++++++++++++++++++++++++-
>>  security/landlock/ruleset.c |  19 +-
>>  security/landlock/ruleset.h |  29 ++-
>>  3 files changed, 433 insertions(+), 4 deletions(-)
>>
>> diff --git a/security/landlock/fs.c b/security/landlock/fs.c
>> index 0b589263ea42..7b0b77859778 100644
>> --- a/security/landlock/fs.c
>> +++ b/security/landlock/fs.c
>> @@ -317,6 +317,207 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
>>  	LANDLOCK_ACCESS_FS_IOCTL_DEV)
>>  /* clang-format on */
>>  
>> +static const struct landlock_rule *find_rule(const struct landlock_ruleset *const domain,
>> +					     const struct dentry *const dentry);
>> +
>> +/**
>> + * landlock_domain_layers_mask - Build a mask covering all layers of a domain
>> + * @domain: The ruleset (domain) to inspect.
>> + *
>> + * Return a layer mask with a 1 bit for each existing layer of @domain.
>> + * If @domain has no layers 0 is returned.  If the number of layers is
>> + * greater than or equal to the number of bits in layer_mask_t, all bits
>> + * are set.
>> + */
>> +static layer_mask_t landlock_domain_layers_mask(const struct landlock_ruleset
>> +						*const domain)
>> +{
>> +	if (!domain || !domain->num_layers)
>> +		return 0;
>> +
>> +	if (domain->num_layers >= sizeof(layer_mask_t) * BITS_PER_BYTE)
>> +		return (layer_mask_t)~0ULL;
>> +
>> +	return GENMASK_ULL(domain->num_layers - 1, 0);
>> +}
>> +
>> +/**
>> + * rule_blocks_all_layers_no_inherit - check whether a rule disables inheritance
>> + * @domain_layers_mask: Mask describing the domain's active layers.
>> + * @rule: Rule to inspect.
>> + *
>> + * Return true if every layer present in @rule has its no_inherit flag set
>> + * and the set of layers covered by the rule equals @domain_layers_mask.
>> + * This indicates that the rule prevents inheritance on all layers of the
>> + * domain and thus further walking for inheritance checks can stop.
>> + */
>> +static bool rule_blocks_all_layers_no_inherit(const layer_mask_t domain_layers_mask,
>> +					      const struct landlock_rule *const rule)
>> +{
>> +	layer_mask_t rule_layers = 0;
>> +	u32 layer_index;
>> +
>> +	if (!domain_layers_mask || !rule)
>> +		return false;
>> +
>> +	for (layer_index = 0; layer_index < rule->num_layers; layer_index++) {
>> +		const struct landlock_layer *const layer =
>> +			&rule->layers[layer_index];
>> +		const layer_mask_t layer_bit = BIT_ULL(layer->level - 1);
>> +
>> +		if (!layer->flags.no_inherit)
>> +			return false;
>> +
>> +		rule_layers |= layer_bit;
>> +	}
>> +
>> +	return rule_layers && rule_layers == domain_layers_mask;
>> +}
>> +
>> +/**
>> + * ensure_rule_for_dentry - ensure a ruleset contains a rule entry for dentry,
>> + * inserting a blank rule if needed.
>> + * @ruleset: Ruleset to modify/inspect.  Caller must hold @ruleset->lock.
>> + * @dentry: Dentry to ensure a rule exists for.
>> + *
>> + * If no rule is currently associated with @dentry, insert an empty rule
>> + * (with zero access) tied to the backing inode.  Returns a pointer to the
>> + * rule associated with @dentry on success, NULL when @dentry is negative, or
>> + * an ERR_PTR()-encoded error if the rule cannot be created.
>> + *
>> + * This is useful for LANDLOCK_ADD_RULE_NO_INHERIT processing, where a rule
>> + * may need to be created for an ancestor dentry that does not yet have one
>> + * to properly track no_inherit flags.
>> + *
>> + * The flags are set to zero if a rule is newly created, and the caller
>> + * is responsible for setting them appropriately.
>> + *
>> + * The returned rule pointer's lifetime is tied to @ruleset.
>> + */
>> +static const struct landlock_rule *
>> +ensure_rule_for_dentry(struct landlock_ruleset *const ruleset,
>> +		       struct dentry *const dentry)
>> +{
>> +	struct landlock_id id = {
>> +		.type = LANDLOCK_KEY_INODE,
>> +	};
>> +	const struct landlock_rule *rule;
>> +	int err;
>> +
>> +	if (WARN_ON_ONCE(!ruleset || !dentry || d_is_negative(dentry)))
>> +		return NULL;
>> +
>> +	lockdep_assert_held(&ruleset->lock);
>> +
>> +	rule = find_rule(ruleset, dentry);
>> +	if (rule)
>> +		return rule;
>> +
>> +	id.key.object = get_inode_object(d_backing_inode(dentry));
>> +	if (IS_ERR(id.key.object))
>> +		return ERR_CAST(id.key.object);
>> +
>> +	err = landlock_insert_rule(ruleset, id, 0, 0);
>> +	landlock_put_object(id.key.object);
>> +	if (err)
>> +		return ERR_PTR(err);
>> +
>> +	rule = find_rule(ruleset, dentry);
>> +	if (WARN_ON_ONCE(!rule))
>> +		return ERR_PTR(-ENOENT);
>> +	return rule;
>> +}
>> +
>> +/**
>> + * mark_no_inherit_ancestors - mark ancestors as having no_inherit descendants
>> + * @ruleset: Ruleset to modify.  Caller must hold @ruleset->lock.
>> + * @path: Path representing the descendant that carries no_inherit bits.
>> + * @descendant_layers: Mask of layers from the descendant that should be
>> + *                     advertised to ancestors via has_no_inherit_descendant.
>> + *
>> + * Walks upward from @dentry and ensures that any ancestor rule contains the
>> + * has_no_inherit_descendant marker for the specified @descendant_layers so
>> + * parent lookups can quickly detect descendant no_inherit influence.
>> + *
>> + * Returns 0 on success or a negative errno if ancestor bookkeeping fails.
>> + */
>> +static int mark_no_inherit_ancestors(struct landlock_ruleset *ruleset,
>> +				     const struct path *const path,
>> +				     layer_mask_t descendant_layers)
>> +{
>> +	struct dentry *cursor;
>> +	struct path walk_path;
>> +	int err = 0;
>> +
>> +	if (WARN_ON_ONCE(!ruleset || !path || !path->dentry || !path->mnt ||
>> +			 !descendant_layers))
>> +		return -EINVAL;
>> +
>> +	lockdep_assert_held(&ruleset->lock);
>> +
>> +	walk_path.mnt = path->mnt;
>> +	walk_path.dentry = path->dentry;
>> +	path_get(&walk_path);
>> +
>> +	cursor = dget(walk_path.dentry);
>> +	while (cursor) {
>> +		struct dentry *parent;
>> +		const struct landlock_rule *rule;
>> +
>> +		/* Follow mounts all the way up to the root. */
>> +		if (IS_ROOT(cursor)) {
>> +			dput(cursor);
>> +			if (!follow_up(&walk_path)) {
>
> This path walk is inconsistent and a duplicate of the (correct)
> is_access_to_paths_allowed() one.  Please add a patch to factor out the
> common parts as much as possible.  Ditto for the
> collect_domain_accesses() and collect_topology_sealed_layers().
>

Total agreement from me.

It makes sense to not duplicate the path traversal code. We could do
everything in is_access_to_paths_allowed but that function is already hairy
in my opinion. What do you think about a helper function for traversal?

        enum landlock_walk_result {
	        LANDLOCK_WALK_CONTINUE,
	        LANDLOCK_WALK_STOP_REAL_ROOT,
	        LANDLOCK_WALK_STOP_INTERNAL_ROOT,
        };

        static enum landlock_walk_result landlock_walk_path(struct path *const path)
        {
        jump_up:
        	if (path->dentry == path->mnt->mnt_root) {
        		if (follow_up(path))
        			goto jump_up;
        		return LANDLOCK_WALK_STOP_REAL_ROOT;
        	}
        
        	if (unlikely(IS_ROOT(path->dentry))) {
        		if (likely(path->mnt->mnt_flags & MNT_INTERNAL))
        			return LANDLOCK_WALK_STOP_INTERNAL_ROOT;
        		dput(path->dentry);
        		path->dentry = dget(path->mnt->mnt_root);
        		return LANDLOCK_WALK_CONTINUE;
        	}
        
        	{
        		struct dentry *const parent = dget_parent(path->dentry);
        
        		dput(path->dentry);
        		path->dentry = parent;
        	}
        	return LANDLOCK_WALK_CONTINUE;
        }

The caller gets a readable enum for where they are in the traversal. This
should centralize the logic and make it easier to
understand.

>> +				cursor = NULL;
>> +				continue;
>> +			}
>> +			cursor = dget(walk_path.dentry);
>> +		}
>> +
>> +		parent = dget_parent(cursor);
>> +		dput(cursor);
>> +		if (!parent)
>> +			break;
>> +
>> +		if (WARN_ON_ONCE(d_is_negative(parent))) {
>> +			dput(parent);
>> +			break;
>> +		}
>> +		/*
>> +		 * Ensures a rule exists for the parent dentry,
>> +		 * inserting a blank one if needed.
>> +		 */
>> +		rule = ensure_rule_for_dentry(ruleset, parent);
>> +		if (IS_ERR(rule)) {
>> +			err = PTR_ERR(rule);
>> +			dput(parent);
>> +			cursor = NULL;
>> +			break;
>> +		}
>> +		if (rule) {
>> +			struct landlock_rule *mutable_rule =
>> +				(struct landlock_rule *)rule;
>> +			/*
>> +			 * Unmerged rulesets should only have one layer.
>> +			 */
>> +			if (WARN_ON_ONCE(mutable_rule->num_layers != 1)) {
>> +				dput(parent);
>> +				err = -EINVAL;
>> +				cursor = NULL;
>> +				break;
>> +			}
>> +
>> +			if (descendant_layers & BIT_ULL(0))
>> +				mutable_rule->layers[0]
>> +					.flags.has_no_inherit_descendant = true;
>> +		}
>> +
>> +		cursor = parent;
>> +	}
>> +	path_put(&walk_path);
>> +	return err;
>> +}
>
>> +/**
>> + * collect_topology_sealed_layers - collect layers sealed against topology changes
>> + * @domain: Ruleset to consult.
>> + * @dentry: Starting dentry for the upward walk.
>> + * @override_layers: Optional out parameter filled with layers that are
>> + *                   present on ancestors but considered overrides (not
>> + *                   sealing the topology for descendants).
>> + *
>> + * Walk upwards from @dentry and return a mask of layers where either the
>> + * visited dentry contains a no_inherit rule or ancestors were previously
>> + * marked as having a descendant with no_inherit.  @override_layers, if not
>> + * NULL, is filled with layers that would normally be overridden by more
>> + * specific descendant rules.
>> + *
>> + * Returns a layer mask where set bits indicate layers that are "sealed"
>> + * (topology changes like rename/rmdir are denied) for the subtree rooted at
>> + * @dentry.
>> + *
>> + * Useful for LANDLOCK_ADD_RULE_NO_INHERIT parent directory enforcement to ensure
>> + * that topology changes do not violate the no_inherit constraints.
>> + */
>> +static layer_mask_t
>> +collect_topology_sealed_layers(const struct landlock_ruleset *const domain,
>> +			       struct dentry *dentry,
>> +			       layer_mask_t *const override_layers)
>> +{
>> +	struct dentry *cursor, *parent;
>> +	bool include_descendants = true;
>> +	layer_mask_t sealed_layers = 0;
>> +
>> +	if (override_layers)
>> +		*override_layers = 0;
>> +
>> +	if (WARN_ON_ONCE(!domain || !dentry || d_is_negative(dentry)))
>> +		return 0;
>> +
>> +	cursor = dget(dentry);
>> +	while (cursor) {
>> +		const struct landlock_rule *rule;
>> +		u32 layer_index;
>> +
>> +		rule = find_rule(domain, cursor);
>> +		if (rule) {
>> +			for (layer_index = 0; layer_index < rule->num_layers;
>> +			     layer_index++) {
>> +				const struct landlock_layer *layer =
>> +					&rule->layers[layer_index];
>> +				layer_mask_t layer_bit =
>> +					BIT_ULL(layer->level - 1);
>> +
>> +				if (include_descendants &&
>> +				    (layer->flags.no_inherit ||
>> +				     layer->flags.has_no_inherit_descendant)) {
>> +					sealed_layers |= layer_bit;
>> +				} else if (override_layers) {
>> +					*override_layers |= layer_bit;
>> +				}
>> +			}
>> +		}
>> +
>> +		if (sealed_layers || IS_ROOT(cursor))
>> +			break;
>> +
>> +		parent = dget_parent(cursor);
>> +		dput(cursor);
>> +		if (!parent)
>> +			return sealed_layers;
>> +
>> +		cursor = parent;
>> +		include_descendants = false;
>> +	}
>> +	dput(cursor);
>> +	return sealed_layers;
>> +}

[PATCH v4 2/5] landlock: Implement LANDLOCK_ADD_RULE_NO_INHERIT userspace api

[Justin Suess]

Implements the syscall side flag handling and kernel api headers for the
LANDLOCK_ADD_RULE_NO_INHERIT flag.

v3..v4 changes:

  * Changed documentation to reflect protections now apply to VFS root
    instead of the mountpoint.

v2..v3 changes:

  * Extended documentation for flag inheritance suppression on
    LANDLOCK_ADD_RULE_NO_INHERIT.
  * Extended the flag validation rules in the syscall.
  * Added mention of no inherit in empty rules in add_rule_path_beneath
    as per Tingmao Wang's suggestion.
  * Added check for useless no-inherit flag in networking rules.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 include/uapi/linux/landlock.h | 29 +++++++++++++++++++++++++++++
 security/landlock/syscalls.c  | 16 ++++++++++++----
 2 files changed, 41 insertions(+), 4 deletions(-)

diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h
index d4f47d20361a..6ab3e7bd1c81 100644
--- a/include/uapi/linux/landlock.h
+++ b/include/uapi/linux/landlock.h
@@ -127,10 +127,39 @@ struct landlock_ruleset_attr {
  *     allowed_access in the passed in rule_attr.  When this flag is
  *     present, the caller is also allowed to pass in an empty
  *     allowed_access.
+ * %LANDLOCK_ADD_RULE_NO_INHERIT
+ *     When set on a rule being added to a ruleset, this flag disables the
+ *     inheritance of access rights and flags from parent objects.
+ *
+ *     This flag currently applies only to filesystem rules.  Adding it to
+ *     non-filesystem rules will return -EINVAL, unless future extensions
+ *     of Landlock define other hierarchical object types.
+ *
+ *     By default, Landlock filesystem rules inherit allowed accesses from
+ *     ancestor directories: if a parent directory grants certain rights,
+ *     those rights also apply to its children.  A rule marked with
+ *     LANDLOCK_ADD_RULE_NO_INHERIT stops this propagation at the directory
+ *     covered by the rule.  Descendants of that directory continue to inherit
+ *     normally unless they also have rules using this flag.
+ *
+ *     If a regular file is marked with this flag, it will not inherit any
+ *     access rights from its parent directories; only the accesses explicitly
+ *     allowed by the rule will apply to that file.
+ *
+ *     This flag also enforces parent-directory restrictions: rename, rmdir,
+ *     link, and other operations that would change the directory's immediate
+ *     parent subtree are denied up to the VFS root.  This prevents
+ *     sandboxed processes from manipulating the filesystem hierarchy to evade
+ *     restrictions (e.g., via sandbox-restart attacks).
+ *
+ *     In addition, this flag blocks the inheritance of rule-layer flags
+ *     (such as the quiet flag) from parent directories to the object covered
+ *     by this rule.
  */
 
 /* clang-format off */
 #define LANDLOCK_ADD_RULE_QUIET			(1U << 0)
+#define LANDLOCK_ADD_RULE_NO_INHERIT		(1U << 1)
 /* clang-format on */
 
 /**
diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
index 5cf1183bb596..0c815e241c75 100644
--- a/security/landlock/syscalls.c
+++ b/security/landlock/syscalls.c
@@ -352,7 +352,7 @@ static int add_rule_path_beneath(struct landlock_ruleset *const ruleset,
 	/*
 	 * Informs about useless rule: empty allowed_access (i.e. deny rules)
 	 * are ignored in path walks.  However, the rule is not useless if it
-	 * is there to hold a quiet flag
+	 * is there to hold a quiet or no inherit flag.
 	 */
 	if (!flags && !path_beneath_attr.allowed_access)
 		return -ENOMSG;
@@ -407,6 +407,10 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
 	if (flags & LANDLOCK_ADD_RULE_QUIET && !ruleset->quiet_masks.net)
 		return -EINVAL;
 
+	/* No inherit is always useless for this scope */
+	if (flags & LANDLOCK_ADD_RULE_NO_INHERIT)
+		return -EINVAL;
+
 	/* Denies inserting a rule with port greater than 65535. */
 	if (net_port_attr.port > U16_MAX)
 		return -EINVAL;
@@ -424,7 +428,7 @@ static int add_rule_net_port(struct landlock_ruleset *ruleset,
  * @rule_type: Identify the structure type pointed to by @rule_attr:
  *             %LANDLOCK_RULE_PATH_BENEATH or %LANDLOCK_RULE_NET_PORT.
  * @rule_attr: Pointer to a rule (matching the @rule_type).
- * @flags: Must be 0 or %LANDLOCK_ADD_RULE_QUIET.
+ * @flags: Must be 0 or %LANDLOCK_ADD_RULE_QUIET and/or %LANDLOCK_ADD_RULE_NO_INHERIT.
  *
  * This system call enables to define a new rule and add it to an existing
  * ruleset.
@@ -462,8 +466,12 @@ SYSCALL_DEFINE4(landlock_add_rule, const int, ruleset_fd,
 
 	if (!is_initialized())
 		return -EOPNOTSUPP;
-
-	if (flags && flags != LANDLOCK_ADD_RULE_QUIET)
+	/* Checks flag existence */
+	if (flags && flags & ~(LANDLOCK_ADD_RULE_QUIET | LANDLOCK_ADD_RULE_NO_INHERIT))
+		return -EINVAL;
+	/* No inherit may only apply on path_beneath rules. */
+	if ((flags & LANDLOCK_ADD_RULE_NO_INHERIT) &&
+	    rule_type != LANDLOCK_RULE_PATH_BENEATH)
 		return -EINVAL;
 
 	/* Gets and checks the ruleset. */
-- 
2.51.0

[PATCH v4 3/5] samples/landlock: Add LANDLOCK_ADD_RULE_NO_INHERIT to landlock-sandboxer

[Justin Suess]

Adds support to landlock-sandboxer with environment variable
LL_FS_NO_INHERIT, which can be tagged on any filesystem object to
suppress access right inheritance.

v3..v4 changes:

  * Modified LL_FS_R(O/W)_NO_INHERIT variables to a single variable
    to allow access rule combination. (credit to Tingmao Wang)

v2..v3 changes:

  * Minor formatting fixes

Cc: Tingmao Wang <m@maowtm.org>
Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 samples/landlock/sandboxer.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/samples/landlock/sandboxer.c b/samples/landlock/sandboxer.c
index 07dc0013ff19..852ffa413c75 100644
--- a/samples/landlock/sandboxer.c
+++ b/samples/landlock/sandboxer.c
@@ -60,6 +60,7 @@ static inline int landlock_restrict_self(const int ruleset_fd,
 #define ENV_FS_RW_NAME "LL_FS_RW"
 #define ENV_FS_QUIET_NAME "LL_FS_QUIET"
 #define ENV_FS_QUIET_ACCESS_NAME "LL_FS_QUIET_ACCESS"
+#define ENV_FS_NO_INHERIT_NAME "LL_FS_NO_INHERIT"
 #define ENV_TCP_BIND_NAME "LL_TCP_BIND"
 #define ENV_TCP_CONNECT_NAME "LL_TCP_CONNECT"
 #define ENV_NET_QUIET_NAME "LL_NET_QUIET"
@@ -383,6 +384,7 @@ static const char help[] =
 	"but to test audit we can set " ENV_FORCE_LOG_NAME "=1\n"
 	ENV_FS_QUIET_NAME " and " ENV_NET_QUIET_NAME ", both optional, can then be used "
 	"to make access to some denied paths or network ports not trigger audit logging.\n"
+	ENV_FS_NO_INHERIT_NAME " can be used to suppress access right propagation (ABI >= 8).\n"
 	ENV_FS_QUIET_ACCESS_NAME " and " ENV_NET_QUIET_ACCESS_NAME " can be used to specify "
 	"which accesses should be quieted (defaults to all):\n"
 	"* " ENV_FS_QUIET_ACCESS_NAME ": file system accesses to quiet\n"
@@ -430,6 +432,7 @@ int main(const int argc, char *const argv[], char *const *const envp)
 	};
 
 	bool quiet_supported = true;
+	bool no_inherit_supported = true;
 	int supported_restrict_flags = LANDLOCK_RESTRICT_SELF_LOG_NEW_EXEC_ON;
 	int set_restrict_flags = 0;
 
@@ -517,8 +520,9 @@ int main(const int argc, char *const argv[], char *const *const envp)
 			LANDLOCK_ABI_LAST, abi);
 		__attribute__((fallthrough));
 	case 7:
-		/* Don't add quiet flags for ABI < 8 later on. */
+		/* Don't add quiet/no_inherit flags for ABI < 8 later on. */
 		quiet_supported = false;
+		no_inherit_supported = false;
 
 		__attribute__((fallthrough));
 	case LANDLOCK_ABI_LAST:
@@ -605,6 +609,13 @@ int main(const int argc, char *const argv[], char *const *const envp)
 			goto err_close_ruleset;
 	}
 
+	/* Don't require this env to be present. */
+	if (no_inherit_supported && getenv(ENV_FS_NO_INHERIT_NAME)) {
+		if (populate_ruleset_fs(ENV_FS_NO_INHERIT_NAME, ruleset_fd, 0,
+					LANDLOCK_ADD_RULE_NO_INHERIT))
+			goto err_close_ruleset;
+	}
+
 	if (populate_ruleset_net(ENV_TCP_BIND_NAME, ruleset_fd,
 				 LANDLOCK_ACCESS_NET_BIND_TCP, 0)) {
 		goto err_close_ruleset;
-- 
2.51.0

[PATCH v4 4/5] selftests/landlock: Implement selftests for LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess]

Implements 15 selftests for the flag, covering allowed and disallowed
operations on parent
and child directories when this flag is set, as well as multi-layer
configurations
and flag inheritance / audit logging. Also tests a bind mount
configuration.

v3..v4 changes:

  * Added 4 new tests for bind mount handling, increasing selftests
    from 11 -> 15.

v2..v3 changes:

  * Also covers flag inheritance, audit logging and
    LANDLOCK_ADD_RULE_QUIET suppression.
  * Increases number of selftests from 5 -> 11.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 tools/testing/selftests/landlock/fs_test.c | 710 +++++++++++++++++++++
 1 file changed, 710 insertions(+)

diff --git a/tools/testing/selftests/landlock/fs_test.c b/tools/testing/selftests/landlock/fs_test.c
index 44e131957fba..079742278969 100644
--- a/tools/testing/selftests/landlock/fs_test.c
+++ b/tools/testing/selftests/landlock/fs_test.c
@@ -1484,6 +1484,111 @@ TEST_F_FORK(layout1, inherit_superset)
 	ASSERT_EQ(0, test_open(file1_s1d3, O_RDONLY));
 }
 
+TEST_F_FORK(layout1, inherit_no_inherit_flag)
+{
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW,
+	};
+	int ruleset_fd;
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RW, dir_s1d1, 0);
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d2,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Parent directory still grants write access to its direct children. */
+	EXPECT_EQ(0, test_open(dir_s1d1, O_RDONLY | O_DIRECTORY));
+	EXPECT_EQ(0, test_open(file1_s1d1, O_WRONLY));
+
+	/* dir_s1d2 gets only its explicit read-only access rights. */
+	EXPECT_EQ(0, test_open(dir_s1d2, O_RDONLY | O_DIRECTORY));
+	EXPECT_EQ(0, test_open(file1_s1d2, O_RDONLY));
+	EXPECT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+
+	/* Descendants of dir_s1d2 inherit the reduced access mask. */
+	EXPECT_EQ(0, test_open(dir_s1d3, O_RDONLY | O_DIRECTORY));
+	EXPECT_EQ(0, test_open(file1_s1d3, O_RDONLY));
+	EXPECT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+}
+
+TEST_F_FORK(layout1, inherit_no_inherit_nested_levels)
+{
+	int ruleset_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				     LANDLOCK_ACCESS_FS_REMOVE_DIR,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Level 1: s1d1 (RW + REFER + REMOVE + NO_INHERIT) */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR,
+			 dir_s1d1, LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	/* Level 2: s1d2 (RO + NO_INHERIT) */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d2,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	/* Level 3: s1d3 (RW + REFER + REMOVE + NO_INHERIT) */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR,
+			 dir_s1d3, LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Level 3: s1d3
+	 * - RW allowed (unlink file)
+	 * - REFER allowed (rename file)
+	 * - REMOVE_DIR denied (parent s1d2 is part of direct parent tree)
+	 */
+	ASSERT_EQ(0, unlink(file1_s1d3));
+	ASSERT_EQ(0, rename(file2_s1d3, file1_s1d3));
+	ASSERT_EQ(0, rename(file1_s1d3, file2_s1d3));
+	ASSERT_EQ(-1, rmdir(dir_s1d3));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Level 2: s1d2
+	 * - RW denied (unlink file), layer is RO
+	 * - REFER denied (rename file)
+	 * - REMOVE_DIR of s1d2 not allowed (parent s1d1 is part of direct parent tree)
+	 */
+	ASSERT_EQ(-1, unlink(file1_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(file2_s1d2, file1_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rmdir(dir_s1d2));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Level 1: s1d1
+	 * - RW allowed
+	 * - Rename allowed (except for direct parent tree s1d2)
+	 * - REMOVE_DIR denied (parent tmp is denied)
+	 */
+	ASSERT_EQ(0, unlink(file1_s1d1));
+	ASSERT_EQ(0, rename(file2_s1d1, file1_s1d1));
+	ASSERT_EQ(0, rename(file1_s1d1, file2_s1d1));
+	ASSERT_EQ(-1, rmdir(dir_s1d1));
+	ASSERT_EQ(EACCES, errno);
+}
+
 TEST_F_FORK(layout0, max_layers)
 {
 	int i, err;
@@ -4408,6 +4513,246 @@ TEST_F_FORK(layout1, named_unix_domain_socket_ioctl)
 	ASSERT_EQ(0, close(cli_fd));
 }
 
+TEST_F_FORK(layout1, inherit_no_inherit_topology_dir)
+{
+	const struct rule rules[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{},
+	};
+	int ruleset_fd;
+
+	ruleset_fd = create_ruleset(_metadata,
+				    ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+				    rules);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Adds a no-inherit rule on a leaf directory. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d3,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Topology modifications of the rule path and its parents are denied.
+	 */
+
+	/* Target directory s1d3 */
+	ASSERT_EQ(-1, rmdir(dir_s1d3));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(dir_s1d3, dir_s2d3));
+	ASSERT_EQ(EACCES, errno);
+
+	/* Parent directory s1d2 */
+	ASSERT_EQ(-1, rmdir(dir_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(dir_s1d2, dir_s2d2));
+	ASSERT_EQ(EACCES, errno);
+
+	/* Grandparent directory s1d1 */
+	ASSERT_EQ(-1, rmdir(dir_s1d1));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(dir_s1d1, dir_s2d1));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Sibling operations are allowed.
+	 */
+	/* Sibling of s1d3 */
+	ASSERT_EQ(0, unlink(file1_s1d2));
+	/* Sibling of s1d2 */
+	ASSERT_EQ(0, unlink(file1_s1d1));
+
+	/*
+	 * Content of the no-inherit directory is restricted by the rule (RO).
+	 */
+	ASSERT_EQ(-1, unlink(file1_s1d3));
+	ASSERT_EQ(EACCES, errno);
+}
+
+TEST_F_FORK(layout1, no_inherit_allow_inner_removal)
+{
+	int ruleset_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE, dir_s1d2,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Content of the no-inherit directory is mutable (RW).
+	 * This checks that the no-inherit flag does not seal the content.
+	 */
+	ASSERT_EQ(0, unlink(file1_s1d2));
+
+	/*
+	 * Topology modifications of the rule path are denied.
+	 */
+	ASSERT_EQ(-1, rmdir(dir_s1d2));
+	ASSERT_EQ(EACCES, errno);
+	ASSERT_EQ(-1, rename(dir_s1d2, dir_s2d2));
+	ASSERT_EQ(EACCES, errno);
+}
+
+TEST_F_FORK(layout1, inherit_no_inherit_topology_unrelated)
+{
+	const struct rule rules[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RW,
+		},
+		{},
+	};
+	static const char unrelated_dir[] = TMP_DIR "/s2d1/unrelated";
+	static const char unrelated_file[] = TMP_DIR "/s2d1/unrelated/f1";
+	int ruleset_fd;
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Adds a no-inherit rule on a leaf directory unrelated to s2. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d3,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Ensure we can still create and delete files outside the sealed branch. */
+	ASSERT_EQ(0, mkdir(unrelated_dir, 0700));
+	ASSERT_EQ(0, mknod(unrelated_file, S_IFREG | 0600, 0));
+	ASSERT_EQ(0, unlink(unrelated_file));
+	ASSERT_EQ(0, rmdir(unrelated_dir));
+
+	/* Existing siblings in s2 remain modifiable. */
+	ASSERT_EQ(0, unlink(file1_s2d1));
+	ASSERT_EQ(0, mknod(file1_s2d1, S_IFREG | 0700, 0));
+}
+
+TEST_F_FORK(layout1, inherit_no_inherit_descendant_rw)
+{
+	const struct rule rules[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RO,
+		},
+		{},
+	};
+	const __u64 handled_access = ACCESS_RW | LANDLOCK_ACCESS_FS_MAKE_REG |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE;
+	static const char child_file[] =
+		TMP_DIR "/s1d1/s1d2/s1d3/rw_descendant";
+	int ruleset_fd;
+
+	ruleset_fd = create_ruleset(_metadata, handled_access, rules);
+	ASSERT_LE(0, ruleset_fd);
+
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d2,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_MAKE_REG |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE,
+			 dir_s1d3, 0);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	ASSERT_EQ(0, mknod(child_file, S_IFREG | 0600, 0));
+	ASSERT_EQ(0, unlink(child_file));
+}
+
+TEST_F_FORK(layout1, inherit_no_inherit_topology_file)
+{
+	const struct rule rules[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RW,
+		},
+		{},
+	};
+	int ruleset_fd;
+	struct landlock_path_beneath_attr path_beneath = {
+		.allowed_access = ACCESS_RO,
+	};
+
+	ruleset_fd = create_ruleset(_metadata, ACCESS_RW, rules);
+	ASSERT_LE(0, ruleset_fd);
+
+	path_beneath.parent_fd = open(file1_s1d2, O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, path_beneath.parent_fd);
+	ASSERT_EQ(-1, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+					&path_beneath,
+					LANDLOCK_ADD_RULE_NO_INHERIT));
+	ASSERT_EQ(EINVAL, errno);
+	ASSERT_EQ(0, close(path_beneath.parent_fd));
+	ASSERT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F_FORK(layout1, inherit_no_inherit_layered)
+{
+	const struct rule layer1_and_2[] = {
+		{
+			.path = TMP_DIR,
+			.access = ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+		},
+		{},
+	};
+	int ruleset_fd;
+	static const char unrelated_dir[] = TMP_DIR "/s2d1/unrelated";
+	static const char unrelated_file[] = TMP_DIR "/s2d1/unrelated/f1";
+
+	/* Layer 1: RW on TMP_DIR */
+	ruleset_fd = create_ruleset(_metadata,
+				    ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+				    layer1_and_2);
+	ASSERT_LE(0, ruleset_fd);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Layer 2: Add no-inherit RO rule on s1d2 */
+	ruleset_fd = create_ruleset(_metadata,
+				    ACCESS_RW | LANDLOCK_ACCESS_FS_REMOVE_FILE,
+				    layer1_and_2);
+	ASSERT_LE(0, ruleset_fd);
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d2,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/* Operations in unrelated areas should still work */
+	ASSERT_EQ(0, mkdir(unrelated_dir, 0700));
+	ASSERT_EQ(0, mknod(unrelated_file, S_IFREG | 0600, 0));
+	ASSERT_EQ(0, unlink(unrelated_file));
+	ASSERT_EQ(0, rmdir(unrelated_dir));
+
+	/* Creating in s1d1 should be allowed (parent still has RW) */
+	ASSERT_EQ(0, mknod(TMP_DIR "/s1d1/newfile", S_IFREG | 0600, 0));
+	ASSERT_EQ(0, unlink(TMP_DIR "/s1d1/newfile"));
+
+	/* Content of s1d2 should be read-only */
+	ASSERT_EQ(-1, unlink(file1_s1d2));
+	ASSERT_EQ(EACCES, errno);
+
+	/* Topology changes to s1d2 should be denied */
+	ASSERT_EQ(-1, rename(dir_s1d2, TMP_DIR "/s2d1/renamed"));
+	ASSERT_EQ(EACCES, errno);
+
+	/* Renaming s1d1 should also be denied (it's an ancestor) */
+	ASSERT_EQ(-1, rename(dir_s1d1, TMP_DIR "/s2d1/renamed"));
+	ASSERT_EQ(EACCES, errno);
+}
+
 /* clang-format off */
 FIXTURE(ioctl) {};
 
@@ -5747,6 +6092,277 @@ TEST_F_FORK(layout4_disconnected_leafs, read_rename_exchange)
 		  test_renameat(s1d42_bind_fd, "f4", s1d42_bind_fd, "f5"));
 }
 
+/*
+ * Test that LANDLOCK_ADD_RULE_NO_INHERIT on a directory accessed via a mount
+ * point protects the parent hierarchy within the mount from topology changes.
+ *
+ * Layout (after bind mount s1d2 -> s2d2):
+ * tmp
+ * ├── s1d1
+ * │   └── s1d2 [source of bind mount]
+ * │       ├── s1d31
+ * │       │   └── s1d41
+ * │       │       ├── f1
+ * │       │       └── f2
+ * │       └── s1d32
+ * │           └── s1d42
+ * │               ├── f3
+ * │               └── f4
+ * └── s2d1
+ *     └── s2d2 [bind mount destination from s1d2]
+ *         ├── s1d31  <- parent of protected dir, should be immovable
+ *         │   └── s1d41  <- protected with NO_INHERIT
+ *         │       ├── f1
+ *         │       └── f2
+ *         └── s1d32
+ *             └── s1d42
+ *                 ├── f3
+ *                 └── f4
+ *
+ * When s1d41 (accessed via the mount at s2d2) is protected with NO_INHERIT,
+ * its parent directories within the mount (s1d31) should be immovable.
+ */
+TEST_F_FORK(layout4_disconnected_leafs, no_inherit_mount_parent_rename)
+{
+	int ruleset_fd, s1d41_bind_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				     LANDLOCK_ACCESS_FS_REMOVE_DIR,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Allow full access to TMP_DIR. */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR,
+			 TMP_DIR, 0);
+
+	/*
+	 * Access s1d41 through the bind mount at s2d2 and protect it with
+	 * NO_INHERIT. This should seal the parent hierarchy through the mount.
+	 */
+	s1d41_bind_fd = open(TMP_DIR "/s2d1/s2d2/s1d31/s1d41",
+			     O_DIRECTORY | O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, s1d41_bind_fd);
+
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				       &(struct landlock_path_beneath_attr){
+					       .parent_fd = s1d41_bind_fd,
+					       .allowed_access = ACCESS_RO,
+				       },
+				       LANDLOCK_ADD_RULE_NO_INHERIT));
+	EXPECT_EQ(0, close(s1d41_bind_fd));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * s1d31 is the parent of s1d41 within the mount. Renaming it should
+	 * be denied because it is part of the protected parent hierarchy.
+	 * Test via the mount path.
+	 */
+	ASSERT_EQ(-1, rename(TMP_DIR "/s2d1/s2d2/s1d31",
+			     TMP_DIR "/s2d1/s2d2/s1d31_renamed"));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * s1d32 is a sibling directory (not in the protected parent chain),
+	 * so renaming it should be allowed.
+	 */
+	ASSERT_EQ(0, rename(TMP_DIR "/s2d1/s2d2/s1d32",
+			    TMP_DIR "/s2d1/s2d2/s1d32_renamed"));
+	ASSERT_EQ(0, rename(TMP_DIR "/s2d1/s2d2/s1d32_renamed",
+			    TMP_DIR "/s2d1/s2d2/s1d32"));
+
+	/*
+	 * Renaming directories not in the protected parent hierarchy should
+	 * still be allowed.
+	 */
+	ASSERT_EQ(0, rename(TMP_DIR "/s3d1", TMP_DIR "/s3d1_renamed"));
+	ASSERT_EQ(0, rename(TMP_DIR "/s3d1_renamed", TMP_DIR "/s3d1"));
+}
+
+TEST_F_FORK(layout4_disconnected_leafs, no_inherit_mount_parent_rmdir)
+{
+	int ruleset_fd, s1d41_bind_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				     LANDLOCK_ACCESS_FS_REMOVE_DIR,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Allow full access to TMP_DIR. */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR,
+			 TMP_DIR, 0);
+
+	/*
+	 * Access s1d41 through the bind mount at s2d2 and protect it with
+	 * NO_INHERIT. This should seal the parent hierarchy through the mount.
+	 */
+	s1d41_bind_fd = open(TMP_DIR "/s2d1/s2d2/s1d31/s1d41",
+			     O_DIRECTORY | O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, s1d41_bind_fd);
+
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				       &(struct landlock_path_beneath_attr){
+					       .parent_fd = s1d41_bind_fd,
+					       .allowed_access = ACCESS_RO,
+				       },
+				       LANDLOCK_ADD_RULE_NO_INHERIT));
+	EXPECT_EQ(0, close(s1d41_bind_fd));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * s1d31 is the parent of s1d41 within the mount. Removing it should
+	 * be denied because it is part of the protected parent hierarchy.
+	 */
+	ASSERT_EQ(-1, rmdir(TMP_DIR "/s2d1/s2d2/s1d31"));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Removing an unrelated directory should still be allowed (if empty).
+	 */
+	ASSERT_EQ(0, rmdir(TMP_DIR "/s3d1"));
+	ASSERT_EQ(0, mkdir(TMP_DIR "/s3d1", 0755));
+}
+
+TEST_F_FORK(layout4_disconnected_leafs, no_inherit_mount_parent_link)
+{
+	int ruleset_fd, s1d41_bind_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				     LANDLOCK_ACCESS_FS_REMOVE_DIR |
+				     LANDLOCK_ACCESS_FS_MAKE_REG,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Allow full access to TMP_DIR. */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR |
+				 LANDLOCK_ACCESS_FS_MAKE_REG,
+			 TMP_DIR, 0);
+
+	/*
+	 * Access s1d41 through the bind mount at s2d2 and protect it with
+	 * NO_INHERIT. This should seal the parent hierarchy through the mount.
+	 */
+	s1d41_bind_fd = open(TMP_DIR "/s2d1/s2d2/s1d31/s1d41",
+			     O_DIRECTORY | O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, s1d41_bind_fd);
+
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				       &(struct landlock_path_beneath_attr){
+					       .parent_fd = s1d41_bind_fd,
+					       .allowed_access = ACCESS_RO,
+				       },
+				       LANDLOCK_ADD_RULE_NO_INHERIT));
+	EXPECT_EQ(0, close(s1d41_bind_fd));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * Creating a hard link within the protected NO_INHERIT directory should
+	 * be denied because NO_INHERIT grants only ACCESS_RO (no MAKE_REG).
+	 */
+	ASSERT_EQ(-1, linkat(AT_FDCWD, TMP_DIR "/s2d1/s2d2/s1d31/s1d41/f1",
+			     AT_FDCWD, TMP_DIR "/s2d1/s2d2/s1d31/s1d41/f1_link",
+			     0));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * Creating links within directories outside the protected chain
+	 * (using the mount source path to avoid EXDEV) should still be allowed.
+	 */
+	ASSERT_EQ(0, linkat(AT_FDCWD, TMP_DIR "/s1d1/s1d2/s1d32/s1d42/f3",
+			    AT_FDCWD, TMP_DIR "/s1d1/s1d2/s1d32/s1d42/f3_link",
+			    0));
+	ASSERT_EQ(0, unlink(TMP_DIR "/s1d1/s1d2/s1d32/s1d42/f3_link"));
+}
+
+/*
+ * Test that NO_INHERIT protection extends to the mount source hierarchy.
+ * If a directory is protected via a mount path, its parents within the
+ * mount source should also be protected from topology changes.
+ */
+TEST_F_FORK(layout4_disconnected_leafs, no_inherit_source_parent_rename)
+{
+	int ruleset_fd, s1d41_bind_fd;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				     LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				     LANDLOCK_ACCESS_FS_REMOVE_DIR,
+	};
+
+	ruleset_fd =
+		landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Allow full access to TMP_DIR. */
+	add_path_beneath(_metadata, ruleset_fd,
+			 ACCESS_RW | LANDLOCK_ACCESS_FS_REFER |
+				 LANDLOCK_ACCESS_FS_REMOVE_FILE |
+				 LANDLOCK_ACCESS_FS_REMOVE_DIR,
+			 TMP_DIR, 0);
+
+	/*
+	 * Access s1d41 through the bind mount at s2d2 and protect it with
+	 * NO_INHERIT. The source mount path parents should also be protected.
+	 */
+	s1d41_bind_fd = open(TMP_DIR "/s2d1/s2d2/s1d31/s1d41",
+			     O_DIRECTORY | O_PATH | O_CLOEXEC);
+	ASSERT_LE(0, s1d41_bind_fd);
+
+	ASSERT_EQ(0, landlock_add_rule(ruleset_fd, LANDLOCK_RULE_PATH_BENEATH,
+				       &(struct landlock_path_beneath_attr){
+					       .parent_fd = s1d41_bind_fd,
+					       .allowed_access = ACCESS_RO,
+				       },
+				       LANDLOCK_ADD_RULE_NO_INHERIT));
+	EXPECT_EQ(0, close(s1d41_bind_fd));
+
+	enforce_ruleset(_metadata, ruleset_fd);
+	ASSERT_EQ(0, close(ruleset_fd));
+
+	/*
+	 * The mount source is s1d1/s1d2. The protected directory s1d41 is at
+	 * s1d1/s1d2/s1d31/s1d41. The parent s1d31 within the mount source
+	 * should be protected from topology changes.
+	 */
+	ASSERT_EQ(-1, rename(TMP_DIR "/s1d1/s1d2/s1d31",
+			     TMP_DIR "/s1d1/s1d2/s1d31_renamed"));
+	ASSERT_EQ(EACCES, errno);
+
+	/*
+	 * s1d32 is a sibling, not in the protected parent chain. It should
+	 * be renamable.
+	 */
+	ASSERT_EQ(0, rename(TMP_DIR "/s1d1/s1d2/s1d32",
+			    TMP_DIR "/s1d1/s1d2/s1d32_renamed"));
+	ASSERT_EQ(0, rename(TMP_DIR "/s1d1/s1d2/s1d32_renamed",
+			    TMP_DIR "/s1d1/s1d2/s1d32"));
+}
+
 /*
  * layout5_disconnected_branch before rename:
  *
@@ -7231,6 +7847,100 @@ TEST_F(audit_layout1, write_file)
 	EXPECT_EQ(1, records.domain);
 }
 
+TEST_F(audit_layout1, no_inherit_parent_is_logged)
+{
+	struct audit_records records;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW,
+	};
+	int ruleset_fd;
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+					     sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Base read-only rule at s1d1. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d1, 0);
+	/* Descendant s1d1/s1d2/s1d3 forbids inheritance but should still log. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d3,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	EXPECT_EQ(EACCES, test_open(file1_s1d2, O_WRONLY));
+	EXPECT_EQ(0, matches_log_fs(_metadata, self->audit_fd,
+				    "fs\\.write_file", file1_s1d2));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(1, records.domain);
+
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F(audit_layout1, no_inherit_blocks_quiet_flag_inheritence)
+{
+	struct audit_records records;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW,
+		.quiet_access_fs = ACCESS_RW,
+	};
+	int ruleset_fd;
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+					     sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Base read-only rule at tmp/s1d1 with quiet flag. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d1,
+			 LANDLOCK_ADD_RULE_QUIET);
+	/* Descendant tmp/s1d1/s1d2/s1d3 forbids inheritance of quiet flag and should still log. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d3,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	EXPECT_EQ(EACCES, test_open(file1_s1d3, O_WRONLY));
+	EXPECT_EQ(0, matches_log_fs(_metadata, self->audit_fd,
+				    "fs\\.write_file", file1_s1d3));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(1, records.domain);
+
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
+TEST_F(audit_layout1, no_inherit_quiet_parent)
+{
+	struct audit_records records;
+	struct landlock_ruleset_attr ruleset_attr = {
+		.handled_access_fs = ACCESS_RW,
+		.quiet_access_fs = ACCESS_RW,
+	};
+	int ruleset_fd;
+
+	ruleset_fd = landlock_create_ruleset(&ruleset_attr,
+					     sizeof(ruleset_attr), 0);
+	ASSERT_LE(0, ruleset_fd);
+
+	/* Base read-only rule at tmp/s1d1 with quiet flag. */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d1,
+			 LANDLOCK_ADD_RULE_QUIET);
+	/* Access to dir_s1d1 shouldn't log */
+	add_path_beneath(_metadata, ruleset_fd, ACCESS_RO, dir_s1d3,
+			 LANDLOCK_ADD_RULE_NO_INHERIT);
+
+	enforce_ruleset(_metadata, ruleset_fd);
+
+	EXPECT_EQ(EACCES, test_open(file1_s1d1, O_WRONLY));
+	EXPECT_NE(0, matches_log_fs(_metadata, self->audit_fd,
+				    "fs\\.write_file", file1_s1d1));
+	EXPECT_EQ(0, audit_count_records(self->audit_fd, &records));
+	EXPECT_EQ(0, records.access);
+	EXPECT_EQ(0, records.domain);
+
+	EXPECT_EQ(0, close(ruleset_fd));
+}
+
 TEST_F(audit_layout1, read_file)
 {
 	struct audit_records records;
-- 
2.51.0

[PATCH v4 5/5] landlock: Implement KUnit test for LANDLOCK_ADD_RULE_NO_INHERIT

[Justin Suess]

Add a unit test for rule_flag collection, ensuring that access masks
are properly propagated with the flags.

No changes in v4.

changes v2..v3:

   * Removing erroneously misplaced code and placed in the proper
     patch.

Signed-off-by: Justin Suess <utilityemal77@gmail.com>
---
 security/landlock/ruleset.c | 89 +++++++++++++++++++++++++++++++++++++
 1 file changed, 89 insertions(+)

diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c
index 9152a939d79a..8064139fde8f 100644
--- a/security/landlock/ruleset.c
+++ b/security/landlock/ruleset.c
@@ -22,6 +22,7 @@
 #include <linux/spinlock.h>
 #include <linux/workqueue.h>
 #include <uapi/linux/landlock.h>
+#include <kunit/test.h>
 
 #include "access.h"
 #include "audit.h"
@@ -770,3 +771,91 @@ landlock_init_layer_masks(const struct landlock_ruleset *const domain,
 	}
 	return handled_accesses;
 }
+
+#ifdef CONFIG_SECURITY_LANDLOCK_KUNIT_TEST
+
+/**
+ * test_unmask_layers_no_inherit - Test landlock_unmask_layers() with no_inherit
+ * @test: The KUnit test context.
+ */
+static void test_unmask_layers_no_inherit(struct kunit *const test)
+{
+	struct landlock_rule *rule;
+	layer_mask_t layer_masks[LANDLOCK_NUM_ACCESS_FS];
+	struct collected_rule_flags rule_flags;
+	const access_mask_t access_request = BIT_ULL(0) | BIT_ULL(1);
+	const layer_mask_t layers_initialized = BIT_ULL(0) | BIT_ULL(1);
+	size_t i;
+
+	rule = kzalloc(struct_size(rule, layers, 2), GFP_KERNEL);
+	KUNIT_ASSERT_NOT_NULL(test, rule);
+
+	rule->num_layers = 2;
+
+	/* Layer 1: allows access 0, no_inherit */
+	rule->layers[0].level = 1;
+	rule->layers[0].access = BIT_ULL(0);
+	rule->layers[0].flags.no_inherit = 1;
+
+	/* Layer 2: allows access 1 */
+	rule->layers[1].level = 2;
+	rule->layers[1].access = BIT_ULL(1);
+
+	/* Case 1: No rule_flags provided (should behave normally) */
+	for (i = 0; i < ARRAY_SIZE(layer_masks); i++)
+		layer_masks[i] = layers_initialized;
+
+	landlock_unmask_layers(rule, access_request, &layer_masks,
+			       ARRAY_SIZE(layer_masks), NULL);
+
+	/* Access 0 should be unmasked by layer 1 */
+	KUNIT_EXPECT_EQ(test, layer_masks[0], layers_initialized & ~BIT_ULL(0));
+	/* Access 1 should be unmasked by layer 2 */
+	KUNIT_EXPECT_EQ(test, layer_masks[1], layers_initialized & ~BIT_ULL(1));
+
+	/* Case 2: rule_flags provided, no existing no_inherit_masks */
+	for (i = 0; i < ARRAY_SIZE(layer_masks); i++)
+		layer_masks[i] = layers_initialized;
+	memset(&rule_flags, 0, sizeof(rule_flags));
+
+	landlock_unmask_layers(rule, access_request, &layer_masks,
+			       ARRAY_SIZE(layer_masks), &rule_flags);
+
+	/* Access 0 should be unmasked by layer 1 */
+	KUNIT_EXPECT_EQ(test, layer_masks[0], layers_initialized & ~BIT_ULL(0));
+	/* Access 1 should be unmasked by layer 2 */
+	KUNIT_EXPECT_EQ(test, layer_masks[1], layers_initialized & ~BIT_ULL(1));
+
+	/* rule_flags should collect no_inherit from layer 1 */
+	KUNIT_EXPECT_EQ(test, rule_flags.no_inherit_masks, (layer_mask_t)BIT_ULL(0));
+
+	/* Case 3: rule_flags provided, layer 1 is masked by no_inherit_masks */
+	for (i = 0; i < ARRAY_SIZE(layer_masks); i++)
+		layer_masks[i] = layers_initialized;
+	memset(&rule_flags, 0, sizeof(rule_flags));
+	rule_flags.no_inherit_masks = BIT_ULL(0); /* Mask layer 1 */
+
+	landlock_unmask_layers(rule, access_request, &layer_masks,
+			       ARRAY_SIZE(layer_masks), &rule_flags);
+
+	/* Access 0 should NOT be unmasked by layer 1 because it is skipped */
+	KUNIT_EXPECT_EQ(test, layer_masks[0], layers_initialized);
+	/* Access 1 should be unmasked by layer 2 */
+	KUNIT_EXPECT_EQ(test, layer_masks[1], layers_initialized & ~BIT_ULL(1));
+
+	kfree(rule);
+}
+
+static struct kunit_case ruleset_test_cases[] = {
+	KUNIT_CASE(test_unmask_layers_no_inherit),
+	{}
+};
+
+static struct kunit_suite ruleset_test_suite = {
+	.name = "landlock_ruleset",
+	.test_cases = ruleset_test_cases,
+};
+
+kunit_test_suite(ruleset_test_suite);
+
+#endif /* CONFIG_SECURITY_LANDLOCK_KUNIT_TEST */
-- 
2.51.0