[PATCH v2] NFSD: Define actions for the new time_deleg FATTR4 attributes

[PATCH v2] NFSD: Define actions for the new time_deleg FATTR4 attributes

[Chuck Lever]

From: Chuck Lever <chuck.lever@oracle.com>

NFSv4 clients won't send legitimate GETATTR requests for these new
attributes because they are intended to be used only with CB_GETATTR
and SETATTR. But NFSD has to do something besides crashing if it
ever sees a GETATTR request that queries these attributes.

RFC 8881 Section 18.7.3 states:

> The server MUST return a value for each attribute that the client
> requests if the attribute is supported by the server for the
> target file system. If the server does not support a particular
> attribute on the target file system, then it MUST NOT return the
> attribute value and MUST NOT set the attribute bit in the result
> bitmap. The server MUST return an error if it supports an
> attribute on the target but cannot obtain its value. In that case,
> no attribute values will be returned.

Further, RFC 9754 Section 5 states:

> These new attributes are invalid to be used with GETATTR, VERIFY,
> and NVERIFY, and they can only be used with CB_GETATTR and SETATTR
> by a client holding an appropriate delegation.

Thus there does not appear to be a specific server response mandated
by specification. Taking the guidance that querying these attributes
via GETATTR is "invalid", NFSD will return nfserr_inval, failing the
request entirely.

Reported-by: Robert Morris <rtm@csail.mit.edu>
Closes: https://lore.kernel.org/linux-nfs/7819419cf0cb50d8130dc6b747765d2b8febc88a.camel@kernel.org/T/#t
Fixes: 51c0d4f7e317 ("nfsd: add support for FATTR4_OPEN_ARGUMENTS")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/nfs4xdr.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
index f4a5e102b63a..e0eb4221cee6 100644
--- a/fs/nfsd/nfs4xdr.c
+++ b/fs/nfsd/nfs4xdr.c
@@ -2939,6 +2939,12 @@ struct nfsd4_fattr_args {
 typedef __be32(*nfsd4_enc_attr)(struct xdr_stream *xdr,
 				const struct nfsd4_fattr_args *args);
 
+static __be32 nfsd4_encode_fattr4__inval(struct xdr_stream *xdr,
+					 const struct nfsd4_fattr_args *args)
+{
+	return nfserr_inval;
+}
+
 static __be32 nfsd4_encode_fattr4__noop(struct xdr_stream *xdr,
 					const struct nfsd4_fattr_args *args)
 {
@@ -3560,6 +3566,8 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
 
 	[FATTR4_MODE_UMASK]		= nfsd4_encode_fattr4__noop,
 	[FATTR4_XATTR_SUPPORT]		= nfsd4_encode_fattr4_xattr_support,
+	[FATTR4_TIME_DELEG_ACCESS]	= nfsd4_encode_fattr4__inval,
+	[FATTR4_TIME_DELEG_MODIFY]	= nfsd4_encode_fattr4__inval,
 	[FATTR4_OPEN_ARGUMENTS]		= nfsd4_encode_fattr4_open_arguments,
 };
 
-- 
2.51.0

Re: [PATCH v2] NFSD: Define actions for the new time_deleg FATTR4 attributes

[Jeff Layton]

On Mon, 2025-09-29 at 12:53 -0400, Chuck Lever wrote:
> From: Chuck Lever <chuck.lever@oracle.com>
> 
> NFSv4 clients won't send legitimate GETATTR requests for these new
> attributes because they are intended to be used only with CB_GETATTR
> and SETATTR. But NFSD has to do something besides crashing if it
> ever sees a GETATTR request that queries these attributes.
> 
> RFC 8881 Section 18.7.3 states:
> 
> > The server MUST return a value for each attribute that the client
> > requests if the attribute is supported by the server for the
> > target file system. If the server does not support a particular
> > attribute on the target file system, then it MUST NOT return the
> > attribute value and MUST NOT set the attribute bit in the result
> > bitmap. The server MUST return an error if it supports an
> > attribute on the target but cannot obtain its value. In that case,
> > no attribute values will be returned.
> 
> Further, RFC 9754 Section 5 states:
> 
> > These new attributes are invalid to be used with GETATTR, VERIFY,
> > and NVERIFY, and they can only be used with CB_GETATTR and SETATTR
> > by a client holding an appropriate delegation.
> 
> Thus there does not appear to be a specific server response mandated
> by specification. Taking the guidance that querying these attributes
> via GETATTR is "invalid", NFSD will return nfserr_inval, failing the
> request entirely.
> 
> Reported-by: Robert Morris <rtm@csail.mit.edu>
> Closes: https://lore.kernel.org/linux-nfs/7819419cf0cb50d8130dc6b747765d2b8febc88a.camel@kernel.org/T/#t
> Fixes: 51c0d4f7e317 ("nfsd: add support for FATTR4_OPEN_ARGUMENTS")
> Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
> ---
>  fs/nfsd/nfs4xdr.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index f4a5e102b63a..e0eb4221cee6 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -2939,6 +2939,12 @@ struct nfsd4_fattr_args {
>  typedef __be32(*nfsd4_enc_attr)(struct xdr_stream *xdr,
>  				const struct nfsd4_fattr_args *args);
>  
> +static __be32 nfsd4_encode_fattr4__inval(struct xdr_stream *xdr,
> +					 const struct nfsd4_fattr_args *args)
> +{
> +	return nfserr_inval;
> +}
> +
>  static __be32 nfsd4_encode_fattr4__noop(struct xdr_stream *xdr,
>  					const struct nfsd4_fattr_args *args)
>  {
> @@ -3560,6 +3566,8 @@ static const nfsd4_enc_attr nfsd4_enc_fattr4_encode_ops[] = {
>  
>  	[FATTR4_MODE_UMASK]		= nfsd4_encode_fattr4__noop,
>  	[FATTR4_XATTR_SUPPORT]		= nfsd4_encode_fattr4_xattr_support,
> +	[FATTR4_TIME_DELEG_ACCESS]	= nfsd4_encode_fattr4__inval,
> +	[FATTR4_TIME_DELEG_MODIFY]	= nfsd4_encode_fattr4__inval,
>  	[FATTR4_OPEN_ARGUMENTS]		= nfsd4_encode_fattr4_open_arguments,
>  };
>  

Reviewed-by: Jeff Layton <jlayton@kernel.org>