Re: [RFC PATCH 4/4] NFSD: Return NFS4ERR_FILE_OPEN only when linking an open file

Jeff Layton
2025-01-23T20:52:28Z

On Thu, 2025-01-23 at 14:52 -0500, cel@kernel.org wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
>
> RFC 8881 Section 18.9.4 paragraphs 1 - 2 tell us that RENAME should
> return NFS4ERR_FILE_OPEN only when the target object is a file that
> is currently open. If the target is a directory, some other status
> must be returned.
>
> Generally I expect that a delegation recall will be triggered in
> some of these circumstances. In other cases, the VFS might return
> -EBUSY for other reasons, and NFSD has to ensure that errno does
> not leak to clients as a status code that is not permitted by spec.
>
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
> fs/nfsd/vfs.c | 44 +++++++++++++++++++++++++++++++-------------
> 1 file changed, 31 insertions(+), 13 deletions(-)
>
> diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> index 5cfb5eb54c23..566b9adf2259 100644
> --- a/fs/nfsd/vfs.c
> +++ b/fs/nfsd/vfs.c
> @@ -1699,9 +1699,17 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
> return err;
> }
>
> -/*
> - * Create a hardlink
> - * N.B. After this call _both_ ffhp and tfhp need an fh_put
> +/**
> + * nfsd_link - create a link
> + * @rqstp: RPC transaction context
> + * @ffhp: the file handle of the directory where the new link is to be created
> + * @name: the filename of the new link
> + * @len: the length of @name in octets
> + * @tfhp: the file handle of an existing file object
> + *
> + * After this call _both_ ffhp and tfhp need an fh_put.
> + *
> + * Returns a generic NFS status code in network byte-order.
> */
> __be32
> nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> @@ -1709,6 +1717,7 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> {
> struct dentry *ddir, *dnew, *dold;
> struct inode *dirp;
> + int type;
> __be32 err;
> int host_err;
>
> @@ -1728,11 +1737,11 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> if (isdotent(name, len))
> goto out;
>
> + err = nfs_ok;
> + type = d_inode(tfhp->fh_dentry)->i_mode & S_IFMT;
> host_err = fh_want_write(tfhp);
> - if (host_err) {
> - err = nfserrno(host_err);
> + if (host_err)
> goto out;
> - }
>
> ddir = ffhp->fh_dentry;
> dirp = d_inode(ddir);
> @@ -1740,7 +1749,7 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
>
> dnew = lookup_one_len(name, ddir, len);
> if (IS_ERR(dnew)) {
> - err = nfserrno(PTR_ERR(dnew));
> + host_err = PTR_ERR(dnew);
> goto out_unlock;
> }
>
> @@ -1756,17 +1765,26 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
> fh_fill_post_attrs(ffhp);
> inode_unlock(dirp);
> if (!host_err) {
> - err = nfserrno(commit_metadata(ffhp));
> - if (!err)
> - err = nfserrno(commit_metadata(tfhp));
> - } else {
> - err = nfserrno(host_err);
> + host_err = commit_metadata(ffhp);
> + if (!host_err)
> + host_err = commit_metadata(tfhp);
> }
> +
> dput(dnew);
> out_drop_write:
> fh_drop_write(tfhp);
> + if (host_err == -EBUSY) {
> + /*
> + * See RFC 8881 Section 18.9.4 para 1-2: NFSv4 LINK
> + * status distinguishes between reg file and dir.
> + */
> + if (type != S_IFDIR)
> + err = nfserr_file_open;
> + else
> + err = nfserr_acces;

I guess nothing in NFS protocol spec prohibits you from hardlinking a
directory, but hopefully any Linux filesystem will be returning -EPERM
when someone tries it! IOW, I suspect the above will probably be dead
code, but I don't think it'll hurt anything.

> + }
> out:
> - return err;
> + return err != nfs_ok ? err : nfserrno(host_err);
>
> out_dput:
> dput(dnew);

--
Jeff Layton <jlayton@kernel.org>