[PATCH 11/13] ovl: use is_subdir() for testing if one thing is a subdir of another

NeilBrown
2026-02-04T05:09:33Z

From: NeilBrown <neil@brown.name>

Rather than using lock_rename(), use the more obvious is_subdir() for
ensuring that neither upper nor workdir contain the other.
Also be explicit in the comment that the two directories cannot be the
same.

As this is a point-it-time sanity check and does not provide any
on-going guarantees, the removal of locking does not introduce any
interesting races.

Signed-off-by: NeilBrown <neil@brown.name>
---
fs/overlayfs/super.c | 15 +++++----------
1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ba9146f22a2c..2fd3e0aee50e 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -451,18 +451,13 @@ static int ovl_lower_dir(const char *name, const struct path *path,
return 0;
}

-/* Workdir should not be subdir of upperdir and vice versa */
+/*
+ * Workdir should not be subdir of upperdir and vice versa, and
+ * they should not be the same.
+ */
static bool ovl_workdir_ok(struct dentry *workdir, struct dentry *upperdir)
{
- bool ok = false;
-
- if (workdir != upperdir) {
- struct dentry *trap = lock_rename(workdir, upperdir);
- if (!IS_ERR(trap))
- unlock_rename(workdir, upperdir);
- ok = (trap == NULL);
- }
- return ok;
+ return !is_subdir(workdir, upperdir) && !is_subdir(upperdir, workdir);
}

static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
--
2.50.0.107.gf914562f5916.dirty