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

[Jeff Layton <jlayton@kernel.org>]

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>