On Mon, 2025-02-17 at 16:30 +1100, NeilBrown wrote:
> vfs_mkdir() does not currently guarantee to leave the child dentry
> hashed or make it positive on success. It may leave it unhashed and
> negative and then the caller needs to perform a lookup to find the
> target dentry, if it needs it.
>
> This patch changes vfs_mkdir() to return the dentry provided by the
> filesystems which is hashed and positive when provided. This reduces
> the need for lookup code which is now included in vfs_mkdir() rather
> than at various call-sites. The included lookup does not include the
> permission check that some of the existing code included in e.g.
> lookup_one_len(). This should not be necessary for lookup up a
> directory which has just be successfully created.
>
> If a different dentry is returned, the first one is put. If necessary
> the fact that it is new can be determined by comparing pointers. A new
> dentry will certainly have a new pointer (as the old is put after the
> new is obtained).
>
> The dentry returned by vfs_mkdir(), when not an error, *is* now
> guaranteed to be hashed and positive.
>
> A few callers do not need the dentry, but will now sometimes perform the
> lookup anyway. This should be cheap except possibly in the case of cifs.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> drivers/base/devtmpfs.c | 7 ++--
> fs/cachefiles/namei.c | 10 +++---
> fs/ecryptfs/inode.c | 14 +++++---
> fs/init.c | 7 ++--
> fs/namei.c | 70 +++++++++++++++++++++++++++++++---------
> fs/nfsd/nfs4recover.c | 7 ++--
> fs/nfsd/vfs.c | 28 +++++-----------
> fs/overlayfs/dir.c | 37 +++------------------
> fs/overlayfs/overlayfs.h | 15 ++++-----
> fs/overlayfs/super.c | 7 ++--
> fs/smb/server/vfs.c | 31 ++++++------------
> fs/xfs/scrub/orphanage.c | 9 +++---
> include/linux/fs.h | 4 +--
> 13 files changed, 121 insertions(+), 125 deletions(-)
>
> diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
> index c9e34842139f..8ec756b5dec4 100644
> --- a/drivers/base/devtmpfs.c
> +++ b/drivers/base/devtmpfs.c
> @@ -160,18 +160,17 @@ static int dev_mkdir(const char *name, umode_t mode)
> {
> struct dentry *dentry;
> struct path path;
> - int err;
>
> dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
> if (IS_ERR(dentry))
> return PTR_ERR(dentry);
>
> - err = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode);
> - if (!err)
> + dentry = vfs_mkdir(&nop_mnt_idmap, d_inode(path.dentry), dentry, mode);
> + if (!IS_ERR(dentry))
> /* mark as kernel-created inode */
> d_inode(dentry)->i_private = &thread;
> done_path_create(&path, dentry);
> - return err;
> + return PTR_ERR_OR_ZERO(dentry);
> }
>
> static int create_path(const char *nodepath)
> diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
> index 7cf59713f0f7..8a8337d1be05 100644
> --- a/fs/cachefiles/namei.c
> +++ b/fs/cachefiles/namei.c
> @@ -95,7 +95,6 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> /* search the current directory for the element name */
> inode_lock_nested(d_inode(dir), I_MUTEX_PARENT);
>
> -retry:
> ret = cachefiles_inject_read_error();
> if (ret == 0)
> subdir = lookup_one_len(dirname, dir, strlen(dirname));
> @@ -128,10 +127,11 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> ret = security_path_mkdir(&path, subdir, 0700);
> if (ret < 0)
> goto mkdir_error;
> - ret = cachefiles_inject_write_error();
> - if (ret == 0)
> - ret = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700);
> - if (ret < 0) {
> + subdir = ERR_PTR(cachefiles_inject_write_error());
> + if (!IS_ERR(subdir))
> + subdir = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700);
> + ret = PTR_ERR(subdir);
> + if (IS_ERR(subdir)) {
> trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
> cachefiles_trace_mkdir_error);
> goto mkdir_error;
> diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
> index 6315dd194228..51a5c54eb740 100644
> --- a/fs/ecryptfs/inode.c
> +++ b/fs/ecryptfs/inode.c
> @@ -511,10 +511,16 @@ static struct dentry *ecryptfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> struct inode *lower_dir;
>
> rc = lock_parent(dentry, &lower_dentry, &lower_dir);
> - if (!rc)
> - rc = vfs_mkdir(&nop_mnt_idmap, lower_dir,
> - lower_dentry, mode);
> - if (rc || d_really_is_negative(lower_dentry))
> + if (rc)
> + goto out;
> +
> + lower_dentry = vfs_mkdir(&nop_mnt_idmap, lower_dir,
> + lower_dentry, mode);
> + rc = PTR_ERR(lower_dentry);
> + if (IS_ERR(lower_dentry))
> + goto out;
> + rc = 0;
> + if (d_unhashed(lower_dentry))
> goto out;
> rc = ecryptfs_interpose(lower_dentry, dentry, dir->i_sb);
> if (rc)
> diff --git a/fs/init.c b/fs/init.c
> index e9387b6c4f30..eef5124885e3 100644
> --- a/fs/init.c
> +++ b/fs/init.c
> @@ -230,9 +230,12 @@ int __init init_mkdir(const char *pathname, umode_t mode)
> return PTR_ERR(dentry);
> mode = mode_strip_umask(d_inode(path.dentry), mode);
> error = security_path_mkdir(&path, dentry, mode);
> - if (!error)
> - error = vfs_mkdir(mnt_idmap(path.mnt), path.dentry->d_inode,
> + if (!error) {
> + dentry = vfs_mkdir(mnt_idmap(path.mnt), path.dentry->d_inode,
> dentry, mode);
> + if (IS_ERR(dentry))
> + error = PTR_ERR(dentry);
> + }
> done_path_create(&path, dentry);
> return error;
> }
> diff --git a/fs/namei.c b/fs/namei.c
> index 19d5ea340a18..f76fee6df369 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4132,7 +4132,8 @@ EXPORT_SYMBOL(kern_path_create);
>
> void done_path_create(struct path *path, struct dentry *dentry)
> {
> - dput(dentry);
> + if (!IS_ERR(dentry))
> + dput(dentry);
> inode_unlock(path->dentry->d_inode);
> mnt_drop_write(path->mnt);
> path_put(path);
> @@ -4278,7 +4279,7 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
> }
>
> /**
> - * vfs_mkdir - create directory
> + * vfs_mkdir - create directory returning correct dentry is possible
> * @idmap: idmap of the mount the inode was found from
> * @dir: inode of the parent directory
> * @dentry: dentry of the child directory
> @@ -4291,9 +4292,20 @@ SYSCALL_DEFINE3(mknod, const char __user *, filename, umode_t, mode, unsigned, d
> * care to map the inode according to @idmap before checking permissions.
> * On non-idmapped mounts or if permission checking is to be performed on the
> * raw inode simply pass @nop_mnt_idmap.
> + *
> + * In the event that the filesystem does not use the *@dentry but leaves it
> + * negative or unhashes it and possibly splices a different one returning it,
> + * the original dentry is dput() and the alternate is returned.
> + *
> + * If the file-system reports success but leaves the dentry unhashed or
> + * negative, a lookup is performed and providing that is positive and
> + * a directory, it will be returned. If the lookup is not successful
> + * the original dentry is unhashed and returned.
> + *
> + * In case of an error the dentry is dput() and an ERR_PTR() is returned.
> */
> -int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> - struct dentry *dentry, umode_t mode)
> +struct dentry *vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> + struct dentry *dentry, umode_t mode)
> {
> int error;
> unsigned max_links = dir->i_sb->s_max_links;
> @@ -4301,30 +4313,54 @@ int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
>
> error = may_create(idmap, dir, dentry);
> if (error)
> - return error;
> + goto err;
>
> + error = -EPERM;
> if (!dir->i_op->mkdir)
> - return -EPERM;
> + goto err;
>
> mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, 0);
> error = security_inode_mkdir(dir, dentry, mode);
> if (error)
> - return error;
> + goto err;
>
> + error = -EMLINK;
> if (max_links && dir->i_nlink >= max_links)
> - return -EMLINK;
> + goto err;
>
> de = dir->i_op->mkdir(idmap, dir, dentry, mode);
> + error = PTR_ERR(de);
> if (IS_ERR(de))
> - return PTR_ERR(de);
> + goto err;
> + if (!de && (d_unhashed(dentry) || d_is_negative(dentry))) {
Would it be better to push this down into the callers that need it and
make returning a hashed, positive dentry a requirement for the mkdir
operation?
You could just turn this block of code into a helper function that
those four filesystems could call, which would mean that you could
avoid the d_unhashed() and d_is_negative() checks on the other
filesystems.
> + /* A few filesystems leave the dentry negative on success,
> + * currently cifs(with posix extensions), kernfs, tracefs, hostfs.
> + * They rely on a subsequent lookup which we perform here.
> + */
> + const struct qstr *d_name = (void*)&dentry->d_name;
> + de = lookup_dcache(d_name, dentry->d_parent, 0);
> + if (!de)
> + de = __lookup_slow(d_name, dentry->d_parent, 0);
> + if (IS_ERR(de))
> + de = NULL;
> + else if (unlikely(d_is_negative(de) || !d_is_dir(de))) {
> + dput(de);
> + de = NULL;
> + }
> + if (!de)
> + /* Ensure caller can easily detect that dentry is not useful */
> + d_drop(dentry);
> + }
> if (de) {
> - fsnotify_mkdir(dir, de);
> - /* Cannot return de yet */
> - dput(de);
> - } else
> - fsnotify_mkdir(dir, dentry);
> + dput(dentry);
> + dentry = de;
> + }
> + fsnotify_mkdir(dir, dentry);
> + return dentry;
>
> - return 0;
> +err:
> + dput(dentry);
> + return ERR_PTR(error);
> }
> EXPORT_SYMBOL(vfs_mkdir);
>
> @@ -4344,8 +4380,10 @@ int do_mkdirat(int dfd, struct filename *name, umode_t mode)
> error = security_path_mkdir(&path, dentry,
> mode_strip_umask(path.dentry->d_inode, mode));
> if (!error) {
> - error = vfs_mkdir(mnt_idmap(path.mnt), path.dentry->d_inode,
> + dentry = vfs_mkdir(mnt_idmap(path.mnt), path.dentry->d_inode,
> dentry, mode);
> + if (IS_ERR(dentry))
> + error = PTR_ERR(dentry);
> }
> done_path_create(&path, dentry);
> if (retry_estale(error, lookup_flags)) {
> diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
> index 28f4d5311c40..c1d9bd07285f 100644
> --- a/fs/nfsd/nfs4recover.c
> +++ b/fs/nfsd/nfs4recover.c
> @@ -233,9 +233,12 @@ nfsd4_create_clid_dir(struct nfs4_client *clp)
> * as well be forgiving and just succeed silently.
> */
> goto out_put;
> - status = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), dentry, S_IRWXU);
> + dentry = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), dentry, S_IRWXU);
> + if (IS_ERR(dentry))
> + status = PTR_ERR(dentry);
> out_put:
> - dput(dentry);
> + if (!status)
> + dput(dentry);
> out_unlock:
> inode_unlock(d_inode(dir));
> if (status == 0) {
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 29cb7b812d71..205b07f21e8d 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1461,7 +1461,7 @@ nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
> struct inode *dirp;
> struct iattr *iap = attrs->na_iattr;
> __be32 err;
> - int host_err;
> + int host_err = 0;
>
> dentry = fhp->fh_dentry;
> dirp = d_inode(dentry);
> @@ -1488,26 +1488,13 @@ nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
> nfsd_check_ignore_resizing(iap);
> break;
> case S_IFDIR:
> - host_err = vfs_mkdir(&nop_mnt_idmap, dirp, dchild, iap->ia_mode);
> - if (!host_err && unlikely(d_unhashed(dchild))) {
> - struct dentry *d;
> - d = lookup_one_len(dchild->d_name.name,
> - dchild->d_parent,
> - dchild->d_name.len);
> - if (IS_ERR(d)) {
> - host_err = PTR_ERR(d);
> - break;
> - }
> - if (unlikely(d_is_negative(d))) {
> - dput(d);
> - err = nfserr_serverfault;
> - goto out;
> - }
> + dchild = vfs_mkdir(&nop_mnt_idmap, dirp, dchild, iap->ia_mode);
> + if (IS_ERR(dchild))
> + host_err = PTR_ERR(dchild);
> + else if (unlikely(dchild != resfhp->fh_dentry)) {
> dput(resfhp->fh_dentry);
> - resfhp->fh_dentry = dget(d);
> + resfhp->fh_dentry = dget(dchild);
> err = fh_update(resfhp);
> - dput(dchild);
> - dchild = d;
> if (err)
> goto out;
> }
> @@ -1530,7 +1517,8 @@ nfsd_create_locked(struct svc_rqst *rqstp, struct svc_fh *fhp,
> err = nfsd_create_setattr(rqstp, fhp, resfhp, attrs);
>
> out:
> - dput(dchild);
> + if (!IS_ERR(dchild))
> + dput(dchild);
> return err;
>
> out_nfserr:
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index 21c3aaf7b274..fe493f3ed6b6 100644
> --- a/fs/overlayfs/dir.c
> +++ b/fs/overlayfs/dir.c
> @@ -138,37 +138,6 @@ int ovl_cleanup_and_whiteout(struct ovl_fs *ofs, struct inode *dir,
> goto out;
> }
>
> -int ovl_mkdir_real(struct ovl_fs *ofs, struct inode *dir,
> - struct dentry **newdentry, umode_t mode)
> -{
> - int err;
> - struct dentry *d, *dentry = *newdentry;
> -
> - err = ovl_do_mkdir(ofs, dir, dentry, mode);
> - if (err)
> - return err;
> -
> - if (likely(!d_unhashed(dentry)))
> - return 0;
> -
> - /*
> - * vfs_mkdir() may succeed and leave the dentry passed
> - * to it unhashed and negative. If that happens, try to
> - * lookup a new hashed and positive dentry.
> - */
> - d = ovl_lookup_upper(ofs, dentry->d_name.name, dentry->d_parent,
> - dentry->d_name.len);
> - if (IS_ERR(d)) {
> - pr_warn("failed lookup after mkdir (%pd2, err=%i).\n",
> - dentry, err);
> - return PTR_ERR(d);
> - }
> - dput(dentry);
> - *newdentry = d;
> -
> - return 0;
> -}
> -
> struct dentry *ovl_create_real(struct ovl_fs *ofs, struct inode *dir,
> struct dentry *newdentry, struct ovl_cattr *attr)
> {
> @@ -191,7 +160,8 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct inode *dir,
>
> case S_IFDIR:
> /* mkdir is special... */
> - err = ovl_mkdir_real(ofs, dir, &newdentry, attr->mode);
> + newdentry = ovl_do_mkdir(ofs, dir, newdentry, attr->mode);
> + err = PTR_ERR_OR_ZERO(newdentry);
> break;
>
> case S_IFCHR:
> @@ -219,7 +189,8 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs, struct inode *dir,
> }
> out:
> if (err) {
> - dput(newdentry);
> + if (!IS_ERR(newdentry))
> + dput(newdentry);
> return ERR_PTR(err);
> }
> return newdentry;
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 0021e2025020..6f2f8f4cfbbc 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -241,13 +241,14 @@ static inline int ovl_do_create(struct ovl_fs *ofs,
> return err;
> }
>
> -static inline int ovl_do_mkdir(struct ovl_fs *ofs,
> - struct inode *dir, struct dentry *dentry,
> - umode_t mode)
> +static inline struct dentry *ovl_do_mkdir(struct ovl_fs *ofs,
> + struct inode *dir,
> + struct dentry *dentry,
> + umode_t mode)
> {
> - int err = vfs_mkdir(ovl_upper_mnt_idmap(ofs), dir, dentry, mode);
> - pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, err);
> - return err;
> + dentry = vfs_mkdir(ovl_upper_mnt_idmap(ofs), dir, dentry, mode);
> + pr_debug("mkdir(%pd2, 0%o) = %i\n", dentry, mode, PTR_ERR_OR_ZERO(dentry));
> + return dentry;
> }
>
> static inline int ovl_do_mknod(struct ovl_fs *ofs,
> @@ -838,8 +839,6 @@ struct ovl_cattr {
>
> #define OVL_CATTR(m) (&(struct ovl_cattr) { .mode = (m) })
>
> -int ovl_mkdir_real(struct ovl_fs *ofs, struct inode *dir,
> - struct dentry **newdentry, umode_t mode);
> struct dentry *ovl_create_real(struct ovl_fs *ofs,
> struct inode *dir, struct dentry *newdentry,
> struct ovl_cattr *attr);
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index 86ae6f6da36b..a381765802e9 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -327,9 +327,10 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> goto retry;
> }
>
> - err = ovl_mkdir_real(ofs, dir, &work, attr.ia_mode);
> - if (err)
> - goto out_dput;
> + work = ovl_do_mkdir(ofs, dir, work, attr.ia_mode);
> + err = PTR_ERR(work);
> + if (IS_ERR(work))
> + goto out_err;
>
> /* Weird filesystem returning with hashed negative (kernfs)? */
> err = -EINVAL;
> diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
> index fe29acef5872..d682443b14ac 100644
> --- a/fs/smb/server/vfs.c
> +++ b/fs/smb/server/vfs.c
> @@ -206,7 +206,7 @@ int ksmbd_vfs_mkdir(struct ksmbd_work *work, const char *name, umode_t mode)
> {
> struct mnt_idmap *idmap;
> struct path path;
> - struct dentry *dentry;
> + struct dentry *dentry, *d;
> int err;
>
> dentry = ksmbd_vfs_kern_path_create(work, name,
> @@ -222,31 +222,18 @@ int ksmbd_vfs_mkdir(struct ksmbd_work *work, const char *name, umode_t mode)
>
> idmap = mnt_idmap(path.mnt);
> mode |= S_IFDIR;
> - err = vfs_mkdir(idmap, d_inode(path.dentry), dentry, mode);
> - if (!err && d_unhashed(dentry)) {
> - struct dentry *d;
> -
> - d = lookup_one(idmap, dentry->d_name.name, dentry->d_parent,
> - dentry->d_name.len);
> - if (IS_ERR(d)) {
> - err = PTR_ERR(d);
> - goto out_err;
> - }
> - if (unlikely(d_is_negative(d))) {
> - dput(d);
> - err = -ENOENT;
> - goto out_err;
> - }
> -
> + d = dentry;
> + entry = vfs_mkdir(idmap, d_inode(path.dentry), dentry, mode);
> + err = PTR_ERR(dentry);
> + if (!IS_ERR(dentry) && dentry != d)
> ksmbd_vfs_inherit_owner(work, d_inode(path.dentry), d_inode(d));
> - dput(d);
> - }
>
> -out_err:
> done_path_create(&path, dentry);
> - if (err)
> + if (IS_ERR(dentry)) {
> pr_err("mkdir(%s): creation failed (err:%d)\n", name, err);
> - return err;
> + return err;
> + }
> + return 0;
> }
>
> static ssize_t ksmbd_vfs_getcasexattr(struct mnt_idmap *idmap,
> diff --git a/fs/xfs/scrub/orphanage.c b/fs/xfs/scrub/orphanage.c
> index c287c755f2c5..3537f3cca6d5 100644
> --- a/fs/xfs/scrub/orphanage.c
> +++ b/fs/xfs/scrub/orphanage.c
> @@ -167,10 +167,11 @@ xrep_orphanage_create(
> * directory to control access to a file we put in here.
> */
> if (d_really_is_negative(orphanage_dentry)) {
> - error = vfs_mkdir(&nop_mnt_idmap, root_inode, orphanage_dentry,
> - 0750);
> - if (error)
> - goto out_dput_orphanage;
> + orphanage_dentry = vfs_mkdir(&nop_mnt_idmap, root_inode,
> + orphanage_dentry, 0750);
> + error = PTR_ERR(orphanage_dentry);
> + if (IS_ERR(orphanage_dentry))
> + goto out_unlock_root;
> }
>
> /* Not a directory? Bail out. */
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 45269608ee23..beae24bc990d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1981,8 +1981,8 @@ bool inode_owner_or_capable(struct mnt_idmap *idmap,
> */
> int vfs_create(struct mnt_idmap *, struct inode *,
> struct dentry *, umode_t, bool);
> -int vfs_mkdir(struct mnt_idmap *, struct inode *,
> - struct dentry *, umode_t);
> +struct dentry *vfs_mkdir(struct mnt_idmap *, struct inode *,
> + struct dentry *, umode_t);
> int vfs_mknod(struct mnt_idmap *, struct inode *, struct dentry *,
> umode_t, dev_t);
> int vfs_symlink(struct mnt_idmap *, struct inode *,
--
Jeff Layton <jlayton@xxxxxxxxxx>
