This helper walks an input path to its parent. Logic are added to handle
walking across mount tree.
This will be used by landlock, and BPF LSM.
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
fs/namei.c | 39 +++++++++++++++++++++++++++++++++++++++
include/linux/namei.h | 8 ++++++++
2 files changed, 47 insertions(+)
diff --git a/fs/namei.c b/fs/namei.c
index 84a0e0b0111c..475f4188a0e6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1379,6 +1379,45 @@ int follow_up(struct path *path)
}
EXPORT_SYMBOL(follow_up);
+/**
+ * path_parent - Find the parent of path
+ * @path: input and output path.
+ *
+ * Given a path, find the parent path. Replace @path with the parent path.
+ * If we were already at the real root or a disconnected root, @path is
+ * not changed.
+ *
+ * Returns:
+ * PATH_PARENT_SAME_MOUNT - if we walked up within the same mount;
+ * PATH_PARENT_CHANGED_MOUNT - if we walked up a mount point;
+ * PATH_PARENT_REAL_ROOT - if we were already at real root;
+ * PATH_PARENT_DISCONNECTED_ROOT - if we were at the root of a disconnected
+ * filesystem.
+ */
+enum path_parent_status path_parent(struct path *path)
+{
+ struct dentry *parent;
+
+ if (path->dentry == path->mnt->mnt_root) {
+ if (!follow_up(path))
+ return PATH_PARENT_REAL_ROOT;
+ return PATH_PARENT_CHANGED_MOUNT;
+ }
+ if (unlikely(IS_ROOT(path->dentry)))
+ return PATH_PARENT_DISCONNECTED_ROOT;
+
+ parent = dget_parent(path->dentry);
+ if (unlikely(!path_connected(path->mnt, parent))) {
+ dput(parent);
+ return PATH_PARENT_DISCONNECTED_ROOT;
+ }
+
+ dput(path->dentry);
+ path->dentry = parent;
+ return PATH_PARENT_SAME_MOUNT;
+}
+EXPORT_SYMBOL_GPL(path_parent);
+
static bool choose_mountpoint_rcu(struct mount *m, const struct path *root,
struct path *path, unsigned *seqp)
{
diff --git a/include/linux/namei.h b/include/linux/namei.h
index bbaf55fb3101..dc6e9096eb15 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -86,6 +86,14 @@ extern int follow_down_one(struct path *);
extern int follow_down(struct path *path, unsigned int flags);
extern int follow_up(struct path *);
+enum path_parent_status {
+ PATH_PARENT_SAME_MOUNT = 0,
+ PATH_PARENT_CHANGED_MOUNT,
+ PATH_PARENT_REAL_ROOT,
+ PATH_PARENT_DISCONNECTED_ROOT,
+};
+enum path_parent_status path_parent(struct path *path);
+
extern struct dentry *lock_rename(struct dentry *, struct dentry *);
extern struct dentry *lock_rename_child(struct dentry *, struct dentry *);
extern void unlock_rename(struct dentry *, struct dentry *);
--
2.47.1
