linux-kernel - [PATCH v4 bpf-next 2/5] landlock: Use path_walk

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Message-ID: <20250611220220.3681382-3-song@kernel.org>
Date: Wed, 11 Jun 2025 15:02:17 -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,
	m@...wtm.org,
	neil@...wn.name,
	Song Liu <song@...nel.org>
Subject: [PATCH v4 bpf-next 2/5] landlock: Use path_walk_parent()

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

No functional changes intended.

Signed-off-by: Song Liu <song@...nel.org>
---
 security/landlock/fs.c | 28 ++++++++--------------------
 1 file changed, 8 insertions(+), 20 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 6fee7c20f64d..63232199ce23 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -837,8 +837,8 @@ static bool is_access_to_paths_allowed(
 	 * restriction.
 	 */
 	while (true) {
-		struct dentry *parent_dentry;
 		const struct landlock_rule *rule;
+		struct path root = {};
 
 		/*
 		 * If at least all accesses allowed on the destination are
@@ -895,35 +895,23 @@ static bool is_access_to_paths_allowed(
 		/* Stops when a rule from each layer grants access. */
 		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))) {
+
+		if (unlikely(IS_ROOT(walker_path.dentry)) &&
+		    (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>).
 			 */
-			if (walker_path.mnt->mnt_flags & MNT_INTERNAL) {
 			allowed_parent1 = true;
 			allowed_parent2 = true;
-			}
 			break;
 		}
-		parent_dentry = dget_parent(walker_path.dentry);
-		dput(walker_path.dentry);
-		walker_path.dentry = parent_dentry;
+		if (!path_walk_parent(&walker_path, &root))
+			break;
 	}
+
+	if (walker_path.dentry)
 		path_put(&walker_path);
 
 	if (!allowed_parent1) {
-- 
2.47.1