On Thu, 2025-02-06 at 16:42 +1100, NeilBrown wrote:
> vfs_mkdir() does not guarantee to make the child dentry positive on
> success. It may leave it negative and then the caller needs to perform a
> lookup to find the target dentry.
>
> This patch introduced vfs_mkdir_return() which performs the lookup if
> needed so that this code is centralised.
>
> This prepares for a new inode operation which will perform mkdir and
> returns the correct dentry.
>
> Signed-off-by: NeilBrown <neilb@xxxxxxx>
> ---
> fs/cachefiles/namei.c | 7 +---
> fs/namei.c | 69 ++++++++++++++++++++++++++++++++++++++++
> fs/nfsd/vfs.c | 21 ++----------
> fs/overlayfs/dir.c | 33 +------------------
> fs/overlayfs/overlayfs.h | 10 +++---
> fs/overlayfs/super.c | 2 +-
> fs/smb/server/vfs.c | 24 +++-----------
> include/linux/fs.h | 2 ++
> 8 files changed, 86 insertions(+), 82 deletions(-)
>
> diff --git a/fs/cachefiles/namei.c b/fs/cachefiles/namei.c
> index 7cf59713f0f7..3c866c3b9534 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));
> @@ -130,7 +129,7 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> goto mkdir_error;
> ret = cachefiles_inject_write_error();
> if (ret == 0)
> - ret = vfs_mkdir(&nop_mnt_idmap, d_inode(dir), subdir, 0700);
> + ret = vfs_mkdir_return(&nop_mnt_idmap, d_inode(dir), &subdir, 0700);
> if (ret < 0) {
> trace_cachefiles_vfs_error(NULL, d_inode(dir), ret,
> cachefiles_trace_mkdir_error);
> @@ -138,10 +137,6 @@ struct dentry *cachefiles_get_directory(struct cachefiles_cache *cache,
> }
> trace_cachefiles_mkdir(dir, subdir);
>
> - if (unlikely(d_unhashed(subdir))) {
> - cachefiles_put_directory(subdir);
> - goto retry;
> - }
> ASSERT(d_backing_inode(subdir));
>
> _debug("mkdir -> %pd{ino=%lu}",
> diff --git a/fs/namei.c b/fs/namei.c
> index 3ab9440c5b93..d98caf36e867 100644
> --- a/fs/namei.c
> +++ b/fs/namei.c
> @@ -4317,6 +4317,75 @@ int vfs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
> }
> EXPORT_SYMBOL(vfs_mkdir);
>
> +/**
> + * vfs_mkdir_return - create directory returning correct dentry
> + * @idmap: idmap of the mount the inode was found from
> + * @dir: inode of the parent directory
> + * @dentryp: pointer to dentry of the child directory
> + * @mode: mode of the child directory
> + *
> + * Create a directory.
> + *
> + * If the inode has been found through an idmapped mount the idmap of
> + * the vfsmount must be passed through @idmap. This function will then take
> + * 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.
> + *
> + * The filesystem may not use the dentry that was passed in. In that case
> + * the passed-in dentry is put and a new one is placed in *@dentryp;
This sounds like the filesystem is not allowed to use the dentry that
we're passing it. Maybe something like this:
"In the event that the filesystem doesn't use *@dentryp, the dentry is
put and a new one is placed in *@dentryp;"
> + * So on successful return *@dentryp will always be positive.
> + */
> +int vfs_mkdir_return(struct mnt_idmap *idmap, struct inode *dir,
> + struct dentry **dentryp, umode_t mode)
> +{
> + struct dentry *dentry = *dentryp;
> + int error;
> + unsigned max_links = dir->i_sb->s_max_links;
> +
> + error = may_create(idmap, dir, dentry);
> + if (error)
> + return error;
> +
> + if (!dir->i_op->mkdir)
> + return -EPERM;
> +
> + mode = vfs_prepare_mode(idmap, dir, mode, S_IRWXUGO | S_ISVTX, 0);
> + error = security_inode_mkdir(dir, dentry, mode);
> + if (error)
> + return error;
> +
> + if (max_links && dir->i_nlink >= max_links)
> + return -EMLINK;
> +
> + error = dir->i_op->mkdir(idmap, dir, dentry, mode);
> + if (!error) {
> + fsnotify_mkdir(dir, dentry);
> + if (unlikely(d_unhashed(dentry))) {
> + struct dentry *d;
> + /* Need a "const" pointer. We know d_name is const
> + * because we hold an exclusive lock on i_rwsem
> + * in d_parent.
> + */
> + const struct qstr *d_name = (void*)&dentry->d_name;
> + d = lookup_dcache(d_name, dentry->d_parent, 0);
> + if (!d)
> + d = __lookup_slow(d_name, dentry->d_parent, 0);
> + if (IS_ERR(d)) {
> + error = PTR_ERR(d);
> + } else if (unlikely(d_is_negative(d))) {
> + dput(d);
> + error = -ENOENT;
> + } else {
> + dput(dentry);
> + *dentryp = d;
> + }
> + }
> + }
> + return error;
> +}
> +EXPORT_SYMBOL(vfs_mkdir_return);
> +
> int do_mkdirat(int dfd, struct filename *name, umode_t mode)
> {
> struct dentry *dentry;
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 29cb7b812d71..740332413138 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1488,26 +1488,11 @@ 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;
> - }
> + host_err = vfs_mkdir_return(&nop_mnt_idmap, dirp, &dchild, iap->ia_mode);
> + if (!host_err && 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;
> }
> diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
> index c9993ff66fc2..e6c54c6ef0f5 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 +160,7 @@ 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);
> + err = ovl_do_mkdir(ofs, dir, &newdentry, attr->mode);
> break;
>
> case S_IFCHR:
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index 0021e2025020..967870f12482 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -242,11 +242,11 @@ static inline int ovl_do_create(struct ovl_fs *ofs,
> }
>
> static inline int ovl_do_mkdir(struct ovl_fs *ofs,
> - struct inode *dir, struct dentry *dentry,
> + 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);
> + int err = vfs_mkdir_return(ovl_upper_mnt_idmap(ofs), dir, dentry, mode);
> + pr_debug("mkdir(%pd2, 0%o) = %i\n", *dentry, mode, err);
> return err;
> }
>
> @@ -838,8 +838,8 @@ 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);
> +int ovl_do_mkdir(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..06ca8b01c336 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -327,7 +327,7 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs,
> goto retry;
> }
>
> - err = ovl_mkdir_real(ofs, dir, &work, attr.ia_mode);
> + err = ovl_do_mkdir(ofs, dir, &work, attr.ia_mode);
> if (err)
> goto out_dput;
>
> diff --git a/fs/smb/server/vfs.c b/fs/smb/server/vfs.c
> index 6890016e1923..4e580bb7baf8 100644
> --- a/fs/smb/server/vfs.c
> +++ b/fs/smb/server/vfs.c
> @@ -211,7 +211,7 @@ 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,
> @@ -227,27 +227,11 @@ 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;
> + err = vfs_mkdir_return(idmap, d_inode(path.dentry), &dentry, mode);
> + if (!err && 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)
> pr_err("mkdir(%s): creation failed (err:%d)\n", name, err);
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index be3ad155ec9f..f81d6bc65fe4 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -1971,6 +1971,8 @@ 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);
> +int vfs_mkdir_return(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>
