linux-kernel - [PATCH bpf-next 2/4] landlock: Use path

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Message-ID: <20250528222623.1373000-3-song@kernel.org>
Date: Wed, 28 May 2025 15:26:21 -0700
From: Song Liu <song@...nel.org>
To: bpf@...r.kernel.org,
	linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org
Cc: kernel-team@...a.com,
	andrii@...nel.org,
	eddyz87@...il.com,
	ast@...nel.org,
	daniel@...earbox.net,
	martin.lau@...ux.dev,
	viro@...iv.linux.org.uk,
	brauner@...nel.org,
	jack@...e.cz,
	kpsingh@...nel.org,
	mattbobrowski@...gle.com,
	amir73il@...il.com,
	repnop@...gle.com,
	jlayton@...nel.org,
	josef@...icpanda.com,
	mic@...ikod.net,
	gnoack@...gle.com,
	Song Liu <song@...nel.org>
Subject: [PATCH bpf-next 2/4] landlock: Use path_parent()

Use path_parent() to walk a path up to its parent.

While path_parent() has an extra check with path_connected() than existing
code, there is no functional changes intended for landlock.

Signed-off-by: Song Liu <song@...nel.org>
---
 security/landlock/fs.c | 34 +++++++++++++++++-----------------
 1 file changed, 17 insertions(+), 17 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 6fee7c20f64d..32a24758ad6e 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -837,7 +837,6 @@ static bool is_access_to_paths_allowed(
 	 * restriction.
 	 */
 	while (true) {
-		struct dentry *parent_dentry;
 		const struct landlock_rule *rule;
 
 		/*
@@ -896,19 +895,17 @@ static bool is_access_to_paths_allowed(
 		if (allowed_parent1 && allowed_parent2)
 			break;
 jump_up:
-		if (walker_path.dentry == walker_path.mnt->mnt_root) {
-			if (follow_up(&walker_path)) {
-				/* Ignores hidden mount points. */
-				goto jump_up;
-			} else {
-				/*
-				 * Stops at the real root.  Denies access
-				 * because not all layers have granted access.
-				 */
-				break;
-			}
-		}
-		if (unlikely(IS_ROOT(walker_path.dentry))) {
+		switch (path_parent(&walker_path)) {
+		case PATH_PARENT_CHANGED_MOUNT:
+			/* Ignores hidden mount points. */
+			goto jump_up;
+		case PATH_PARENT_REAL_ROOT:
+			/*
+			 * Stops at the real root.  Denies access
+			 * because not all layers have granted access.
+			 */
+			goto walk_done;
+		case PATH_PARENT_DISCONNECTED_ROOT:
 			/*
 			 * Stops at disconnected root directories.  Only allows
 			 * access to internal filesystems (e.g. nsfs, which is
@@ -918,12 +915,15 @@ static bool is_access_to_paths_allowed(
 				allowed_parent1 = true;
 				allowed_parent2 = true;
 			}
+			goto walk_done;
+		case PATH_PARENT_SAME_MOUNT:
 			break;
+		default:
+			WARN_ON_ONCE(1);
+			goto walk_done;
 		}
-		parent_dentry = dget_parent(walker_path.dentry);
-		dput(walker_path.dentry);
-		walker_path.dentry = parent_dentry;
 	}
+walk_done:
 	path_put(&walker_path);
 
 	if (!allowed_parent1) {
-- 
2.47.1