[PATCH v5 07/14] VFS: introduce start_removing_dentry()

NeilBrown
2025-11-06T00:55:33Z

From: NeilBrown <neil@brown.name>

start_removing_dentry() is similar to start_removing() but instead of
providing a name for lookup, the target dentry is given.

start_removing_dentry() checks that the dentry is still hashed and in
the parent, and if so it locks and increases the refcount so that
end_removing() can be used to finish the operation.

This is used in cachefiles, overlayfs, smb/server, and apparmor.

There will be other users including ecryptfs.

As start_removing_dentry() takes an extra reference to the dentry (to be
put by end_removing()), there is no need to explicitly take an extra
reference to stop d_delete() from using dentry_unlink_inode() to negate
the dentry - as in cachefiles_delete_object(), and ksmbd_vfs_unlink().

cachefiles_bury_object() now gets an extra ref to the victim, which is
drops. As it includes the needed end_removing() calls, the caller
doesn't need them.

Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: NeilBrown <neil@brown.name>

---
Changes since v4
Callers of cachefiles_bury_object() were incorrectly calling
end_removing() after that call. The dput() was needed, the unlock
wasn't. The dput() has been effectively moved into
cachefiles_bury_object() by removing a dget() which is now not needed.
---
fs/cachefiles/interface.c | 11 +++++++----
fs/cachefiles/namei.c | 30 ++++++++++++++----------------
fs/cachefiles/volume.c | 9 ++++++---
fs/namei.c | 33 +++++++++++++++++++++++++++++++++
fs/overlayfs/dir.c | 10 ++++------
fs/overlayfs/readdir.c | 8 ++++----
fs/smb/server/vfs.c | 27 ++++-----------------------
include/linux/namei.h | 2 ++
security/apparmor/apparmorfs.c | 8 ++++----
9 files changed, 78 insertions(+), 60 deletions(-)

diff --git a/fs/cachefiles/interface.c b/fs/cachefiles/interface.c
index 3e63cfe15874..a08250d244ea 100644
--- a/fs/cachefiles/interface.c
+++ b/fs/cachefiles/interface.c
@@ -9,6 +9,7 @@
#include <linux/mount.h>
#include <linux/xattr.h>
#include <linux/file.h>
+#include <linux/namei.h>
#include <linux/falloc.h>
#include <trace/events/fscache.h>
#include "internal.h"
@@ -428,11 +429,13 @@ static bool cachefiles_invalidate_cookie(struct fscache_cookie *cookie)
if (!old_tmpfile) {
struct cachefiles_volume *volume = object->volume;
struct dentry *fan = volume->fanout[(u8)cookie->key_hash];
+ struct dentry *obj;

- inode_lock_nested(d_inode(fan), I_MUTEX_PARENT);
- cachefiles_bury_object(volume->cache, object, fan,
- old_file->f_path.dentry,
- FSCACHE_OBJECT_INVALIDATED);
+ obj = start_removing_dentry(fan, old_file->f_path.dentry);
+ if (!IS_ERR(obj))
+ cachefiles_bury_object(volume->cache, object,
+ fan, obj,
+ FSCACHE_OBJECT_INVALIDATED);
}
fput(old_file);
}
diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
index c7f0c6ab9b88..0104ac00485d 100644
--- a/fs/cachefiles/namei.c
+++ b/fs/cachefiles/namei.c
@@ -261,6 +261,7 @@ static int cachefiles_unlink(struct cachefiles_cache *cache,
* - Directory backed objects are stuffed into the graveyard for userspace to
* delete
* On entry dir must be locked. It will be unlocked on exit.
+ * On entry there must be at least 2 refs on rep, one will be dropped on exit.
*/
int cachefiles_bury_object(struct cachefiles_cache *cache,
struct cachefiles_object *object,
@@ -275,12 +276,6 @@ int cachefiles_bury_object(struct cachefiles_cache *cache,

_enter(",'%pd','%pd'", dir, rep);

- /* end_removing() will dput() @rep but we need to keep
- * a ref, so take one now. This also stops the dentry
- * being negated when unlinked which we need.
- */
- dget(rep);
-
if (rep->d_parent != dir) {
end_removing(rep);
_leave(" = -ESTALE");
@@ -425,13 +420,12 @@ int cachefiles_delete_object(struct cachefiles_object *object,

_enter(",OBJ%x{%pD}", object->debug_id, object->file);

- /* Stop the dentry being negated if it's only pinned by a file struct. */
- dget(dentry);
-
- inode_lock_nested(d_backing_inode(fan), I_MUTEX_PARENT);
- ret = cachefiles_unlink(volume->cache, object, fan, dentry, why);
- inode_unlock(d_backing_inode(fan));
- dput(dentry);
+ dentry = start_removing_dentry(fan, dentry);
+ if (IS_ERR(dentry))
+ ret = PTR_ERR(dentry);
+ else
+ ret = cachefiles_unlink(volume->cache, object, fan, dentry, why);
+ end_removing(dentry);
return ret;
}

@@ -644,9 +638,13 @@ bool cachefiles_look_up_object(struct cachefiles_object *object)

if (!d_is_reg(dentry)) {
pr_err("%pd is not a file\n", dentry);
- inode_lock_nested(d_inode(fan), I_MUTEX_PARENT);
- ret = cachefiles_bury_object(volume->cache, object, fan, dentry,
- FSCACHE_OBJECT_IS_WEIRD);
+ struct dentry *de = start_removing_dentry(fan, dentry);
+ if (IS_ERR(de))
+ ret = PTR_ERR(de);
+ else
+ ret = cachefiles_bury_object(volume->cache, object,
+ fan, de,
+ FSCACHE_OBJECT_IS_WEIRD);
dput(dentry);
if (ret < 0)
return false;
diff --git a/fs/cachefiles/volume.c b/fs/cachefiles/volume.c
index 781aac4ef274..90ba926f488e 100644
--- a/fs/cachefiles/volume.c
+++ b/fs/cachefiles/volume.c
@@ -7,6 +7,7 @@

#include <linux/fs.h>
#include <linux/slab.h>
+#include <linux/namei.h>
#include "internal.h"
#include <trace/events/fscache.h>

@@ -58,9 +59,11 @@ void cachefiles_acquire_volume(struct fscache_volume *vcookie)
if (ret < 0) {
if (ret != -ESTALE)
goto error_dir;
- inode_lock_nested(d_inode(cache->store), I_MUTEX_PARENT);
- cachefiles_bury_object(cache, NULL, cache->store, vdentry,
- FSCACHE_VOLUME_IS_WEIRD);
+ vdentry = start_removing_dentry(cache->store, vdentry);
+ if (!IS_ERR(vdentry))
+ cachefiles_bury_object(cache, NULL, cache->store,
+ vdentry,
+ FSCACHE_VOLUME_IS_WEIRD);
cachefiles_put_directory(volume->dentry);
cond_resched();
goto retry;
diff --git a/fs/namei.c b/fs/namei.c
index da01b828ede6..729b42fb143b 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3323,6 +3323,39 @@ struct dentry *start_removing_noperm(struct dentry *parent,
}
EXPORT_SYMBOL(start_removing_noperm);

+/**
+ * start_removing_dentry - prepare to remove a given dentry
+ * @parent: directory from which dentry should be removed
+ * @child: the dentry to be removed
+ *
+ * A lock is taken to protect the dentry again other dirops and
+ * the validity of the dentry is checked: correct parent and still hashed.
+ *
+ * If the dentry is valid and positive, a reference is taken and
+ * returned. If not an error is returned.
+ *
+ * end_removing() should be called when removal is complete, or aborted.
+ *
+ * Returns: the valid dentry, or an error.
+ */
+struct dentry *start_removing_dentry(struct dentry *parent,
+ struct dentry *child)
+{
+ inode_lock_nested(parent->d_inode, I_MUTEX_PARENT);
+ if (unlikely(IS_DEADDIR(parent->d_inode) ||
+ child->d_parent != parent ||
+ d_unhashed(child))) {
+ inode_unlock(parent->d_inode);
+ return ERR_PTR(-EINVAL);
+ }
+ if (d_is_negative(child)) {
+ inode_unlock(parent->d_inode);
+ return ERR_PTR(-ENOENT);
+ }
+ return dget(child);
+}
+EXPORT_SYMBOL(start_removing_dentry);
+
#ifdef CONFIG_UNIX98_PTYS
int path_pts(struct path *path)
{
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 20682afdbd20..6d1d0e94e287 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -47,14 +47,12 @@ static int ovl_cleanup_locked(struct ovl_fs *ofs, struct inode *wdir,
int ovl_cleanup(struct ovl_fs *ofs, struct dentry *workdir,
struct dentry *wdentry)
{
- int err;
-
- err = ovl_parent_lock(workdir, wdentry);
- if (err)
- return err;
+ wdentry = start_removing_dentry(workdir, wdentry);
+ if (IS_ERR(wdentry))
+ return PTR_ERR(wdentry);

ovl_cleanup_locked(ofs, workdir->d_inode, wdentry);
- ovl_parent_unlock(workdir);
+ end_removing(wdentry);

return 0;
}
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index 1e9792cc557b..77ecc39fc33a 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -1242,11 +1242,11 @@ int ovl_workdir_cleanup(struct ovl_fs *ofs, struct dentry *parent,
if (!d_is_dir(dentry) || level > 1)
return ovl_cleanup(ofs, parent, dentry);

- err = ovl_parent_lock(parent, dentry);
- if (err)
- return err;
+ dentry = start_removing_dentry(parent, dentry);
+ if (IS_ERR(dentry))
+ return PTR_ERR(dentry);
err = ovl_do_rmdir(ofs, parent->d_inode, dentry);
- ovl_parent_unlock(parent);
+ end_removing(dentry);
if (err) {
struct path path = { .mnt = mnt, .dentry = dentry };

diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
index 891ed2dc2b73..7c4ddc43ab39 100644
--- a/fs/smb/server/vfs.c
+++ b/fs/smb/server/vfs.c
@@ -49,24 +49,6 @@ static void ksmbd_vfs_inherit_owner(struct ksmbd_work *work,
i_uid_write(inode, i_uid_read(parent_inode));
}

-/**
- * ksmbd_vfs_lock_parent() - lock parent dentry if it is stable
- * @parent: parent dentry
- * @child: child dentry
- *
- * Returns: %0 on success, %-ENOENT if the parent dentry is not stable
- */
-int ksmbd_vfs_lock_parent(struct dentry *parent, struct dentry *child)
-{
- inode_lock_nested(d_inode(parent), I_MUTEX_PARENT);
- if (child->d_parent != parent) {
- inode_unlock(d_inode(parent));
- return -ENOENT;
- }
-
- return 0;
-}
-
static int ksmbd_vfs_path_lookup(struct ksmbd_share_config *share_conf,
char *pathname, unsigned int flags,
struct path *path, bool do_lock)
@@ -1084,18 +1066,17 @@ int ksmbd_vfs_unlink(struct file *filp)
return err;

dir = dget_parent(dentry);
- err = ksmbd_vfs_lock_parent(dir, dentry);
- if (err)
+ dentry = start_removing_dentry(dir, dentry);
+ err = PTR_ERR(dentry);
+ if (IS_ERR(dentry))
goto out;
- dget(dentry);

if (S_ISDIR(d_inode(dentry)->i_mode))
err = vfs_rmdir(idmap, d_inode(dir), dentry);
else
err = vfs_unlink(idmap, d_inode(dir), dentry, NULL);

- dput(dentry);
- inode_unlock(d_inode(dir));
+ end_removing(dentry);
if (err)
ksmbd_debug(VFS, "failed to delete, err %d\n", err);
out:
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 0441f5921f87..d089e4e8fdd0 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -95,6 +95,8 @@ struct dentry *start_removing(struct mnt_idmap *idmap, struct dentry *parent,
struct qstr *name);
struct dentry *start_creating_noperm(struct dentry *parent, struct qstr *name);
struct dentry *start_removing_noperm(struct dentry *parent, struct qstr *name);
+struct dentry *start_removing_dentry(struct dentry *parent,
+ struct dentry *child);

/**
* end_creating - finish action started with start_creating
diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 391a586d0557..9d08d103f142 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -355,17 +355,17 @@ static void aafs_remove(struct dentry *dentry)
if (!dentry || IS_ERR(dentry))
return;

+ /* ->d_parent is stable as rename is not supported */
dir = d_inode(dentry->d_parent);
- inode_lock(dir);
- if (simple_positive(dentry)) {
+ dentry = start_removing_dentry(dentry->d_parent, dentry);
+ if (!IS_ERR(dentry) && simple_positive(dentry)) {
if (d_is_dir(dentry))
simple_rmdir(dir, dentry);
else
simple_unlink(dir, dentry);
d_delete(dentry);
- dput(dentry);
}
- inode_unlock(dir);
+ end_removing(dentry);
simple_release_fs(&aafs_mnt, &aafs_count);
}

--
2.50.0.107.gf914562f5916.dirty