[PATCH 29/29] nfsd: only allow filesystems that set EXPORT_OP_STABLE_HANDLES

[Amir Goldstein]

On Thu, Jan 15, 2026 at 6:51 PM Jeff Layton <jlayton at kernel.org> wrote:
>
> Some filesystems have grown export operations in order to provide
> filehandles for local usage. Some of these filesystems are unsuitable
> for use with nfsd, since their filehandles are not persistent across
> reboots.
>
> In __fh_verify, check whether EXPORT_OP_STABLE_HANDLES is set
> and return nfserr_stale if it isn't.
>
> Signed-off-by: Jeff Layton <jlayton at kernel.org>
> ---
>  fs/nfsd/nfsfh.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
> index ed85dd43da18e6d4c4667ff14dc035f2eacff1d6..da9d5fb2e6613c2707195da2e8678b3fcb3d444d 100644
> --- a/fs/nfsd/nfsfh.c
> +++ b/fs/nfsd/nfsfh.c
> @@ -334,6 +334,10 @@ __fh_verify(struct svc_rqst *rqstp,
>         dentry = fhp->fh_dentry;
>         exp = fhp->fh_export;
>
> +       error = nfserr_stale;
> +       if (!(dentry->d_sb->s_export_op->flags & EXPORT_OP_STABLE_HANDLES))
> +               goto out;
> +
>         trace_nfsd_fh_verify(rqstp, fhp, type, access);
>

IDGI. Don't you want  to deny the export of those fs in check_export()?
By the same logic that check_export() checks for can_decode_fh()
not for can_encode_fh().

Thanks,
Amir.