Merge tag 'landlock-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux

Pull landlock updates from Mickaël Salaün:
 "This mainly fixes handling of disconnected directories and adds new
  tests"

* tag 'landlock-6.19-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/mic/linux:
  selftests/landlock: Add disconnected leafs and branch test suites
  selftests/landlock: Add tests for access through disconnected paths
  landlock: Improve variable scope
  landlock: Fix handling of disconnected directories
  selftests/landlock: Fix makefile header list
  landlock: Make docs in cred.h and domain.h visible
  landlock: Minor comments improvements

Documentation/security/landlock.rst

@@ -7,7 +7,7 @@ Landlock LSM: kernel documentation
 ==================================
 
 :Author: Mickaël Salaün
-:Date: March 2025
+:Date: September 2025
 
 Landlock's goal is to create scoped access-control (i.e. sandboxing).  To
 harden a whole system, this feature should be available to any process,
@@ -110,6 +110,12 @@ Filesystem
 .. kernel-doc:: security/landlock/fs.h
     :identifiers:
 
+Process credential
+------------------
+
+.. kernel-doc:: security/landlock/cred.h
+    :identifiers:
+
 Ruleset and domain
 ------------------
 
@@ -128,6 +134,9 @@ makes the reasoning much easier and helps avoid pitfalls.
 .. kernel-doc:: security/landlock/ruleset.h
     :identifiers:
 
+.. kernel-doc:: security/landlock/domain.h
+    :identifiers:
+
 Additional documentation
 ========================
 

security/landlock/errata/abi-1.h

@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+/**
+ * DOC: erratum_3
+ *
+ * Erratum 3: Disconnected directory handling
+ * ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ *
+ * This fix addresses an issue with disconnected directories that occur when a
+ * directory is moved outside the scope of a bind mount.  The change ensures
+ * that evaluated access rights include both those from the disconnected file
+ * hierarchy down to its filesystem root and those from the related mount point
+ * hierarchy.  This prevents access right widening through rename or link
+ * actions.
+ */
+LANDLOCK_ERRATUM(3)

security/landlock/fs.c

@@ -714,7 +714,8 @@ static void test_is_eacces_with_write(struct kunit *const test)
  * is_access_to_paths_allowed - Check accesses for requests with a common path
  *
  * @domain: Domain to check against.
- * @path: File hierarchy to walk through.
+ * @path: File hierarchy to walk through.  For refer checks, this would be
+ *     the common mountpoint.
  * @access_request_parent1: Accesses to check, once @layer_masks_parent1 is
  *     equal to @layer_masks_parent2 (if any).  This is tied to the unique
  *     requested path for most actions, or the source in case of a refer action
@@ -837,7 +838,6 @@ static bool is_access_to_paths_allowed(
 	 * restriction.
 	 */
 	while (true) {
-		struct dentry *parent_dentry;
 		const struct landlock_rule *rule;
 
 		/*
@@ -909,22 +909,34 @@ jump_up:
 				break;
 			}
 		}
+
 		if (unlikely(IS_ROOT(walker_path.dentry))) {
+			if (likely(walker_path.mnt->mnt_flags & MNT_INTERNAL)) {
 				/*
-			 * Stops at disconnected root directories.  Only allows
-			 * access to internal filesystems (e.g. nsfs, which is
-			 * reachable through /proc/<pid>/ns/<namespace>).
+				 * Stops and allows access when reaching disconnected root
+				 * directories that are part of internal filesystems (e.g. nsfs,
+				 * which is reachable through /proc/<pid>/ns/<namespace>).
 				 */
-			if (walker_path.mnt->mnt_flags & MNT_INTERNAL) {
 				allowed_parent1 = true;
 				allowed_parent2 = true;
-			}
 				break;
 			}
-		parent_dentry = dget_parent(walker_path.dentry);
+
+			/*
+			 * We reached a disconnected root directory from a bind mount.
+			 * Let's continue the walk with the mount point we missed.
+			 */
+			dput(walker_path.dentry);
+			walker_path.dentry = walker_path.mnt->mnt_root;
+			dget(walker_path.dentry);
+		} else {
+			struct dentry *const parent_dentry =
+				dget_parent(walker_path.dentry);
+
 			dput(walker_path.dentry);
 			walker_path.dentry = parent_dentry;
 		}
+	}
 	path_put(&walker_path);
 
 	if (!allowed_parent1) {
@@ -1021,6 +1033,9 @@ static access_mask_t maybe_remove(const struct dentry *const dentry)
  * file.  While walking from @dir to @mnt_root, we record all the domain's
  * allowed accesses in @layer_masks_dom.
  *
+ * Because of disconnected directories, this walk may not reach @mnt_dir.  In
+ * this case, the walk will continue to @mnt_dir after this call.
+ *
  * This is similar to is_access_to_paths_allowed() but much simpler because it
  * only handles walking on the same mount point and only checks one set of
  * accesses.
@@ -1062,8 +1077,11 @@ static bool collect_domain_accesses(
 			break;
 		}
 
-		/* We should not reach a root other than @mnt_root. */
-		if (dir == mnt_root || WARN_ON_ONCE(IS_ROOT(dir)))
+		/*
+		 * Stops at the mount point or the filesystem root for a disconnected
+		 * directory.
+		 */
+		if (dir == mnt_root || unlikely(IS_ROOT(dir)))
 			break;
 
 		parent_dentry = dget_parent(dir);

security/landlock/ruleset.c

@@ -83,6 +83,10 @@ static void build_check_rule(void)
 		.num_layers = ~0,
 	};
 
+	/*
+	 * Checks that .num_layers is large enough for at least
+	 * LANDLOCK_MAX_NUM_LAYERS layers.
+	 */
 	BUILD_BUG_ON(rule.num_layers < LANDLOCK_MAX_NUM_LAYERS);
 }
 
@@ -290,6 +294,10 @@ static void build_check_layer(void)
 		.access = ~0,
 	};
 
+	/*
+	 * Checks that .level and .access are large enough to contain their expected
+	 * maximum values.
+	 */
 	BUILD_BUG_ON(layer.level < LANDLOCK_MAX_NUM_LAYERS);
 	BUILD_BUG_ON(layer.access < LANDLOCK_MASK_ACCESS_FS);
 }
@@ -644,8 +652,8 @@ bool landlock_unmask_layers(const struct landlock_rule *const rule,
 		bool is_empty;
 
 		/*
-		 * Records in @layer_masks which layer grants access to each
-		 * requested access.
+		 * Records in @layer_masks which layer grants access to each requested
+		 * access: bit cleared if the related layer grants access.
 		 */
 		is_empty = true;
 		for_each_set_bit(access_bit, &access_req, masks_array_size) {

security/landlock/ruleset.h

@@ -27,7 +27,7 @@ struct landlock_hierarchy;
  */
 struct landlock_layer {
 	/**
-	 * @level: Position of this layer in the layer stack.
+	 * @level: Position of this layer in the layer stack.  Starts from 1.
 	 */
 	u16 level;
 	/**

tools/testing/selftests/landlock/Makefile

@@ -4,7 +4,7 @@
 
 CFLAGS += -Wall -O2 $(KHDR_INCLUDES)
 
-LOCAL_HDRS += common.h
+LOCAL_HDRS += $(wildcard *.h)
 
 src_test := $(wildcard *_test.c)