NFSD: Fix callback decoder status codes

fs/nfsd/nfs4callback.c implements a callback client. Thus its XDR
decoders are decoding replies, not calls.

NFS4ERR_BAD_XDR is an on-the-wire status code that reports that the
client sent a corrupted RPC /call/. It's not used as the internal
error code when a /reply/ can't be decoded, since that kind of
failure is never reported to the sender of that RPC message.

Instead, a reply decoder should return -EIO, as the reply decoders
in the NFS client do.

Fixes: 6487a13b5c6b ("NFSD: add support for CB_GETATTR callback")
Reviewed-by: Jeff Layton <[e-mail]>
Signed-off-by: Chuck Lever <[e-mail]>

fs/nfsd/nfs4callback.c

···
 
 	if (bitmap[0] & FATTR4_WORD0_CHANGE)
 		if (xdr_stream_decode_u64(xdr, &fattr->ncf_cb_change) < 0)
-			return -NFSERR_BAD_XDR;
+			return -EIO;
 	if (bitmap[0] & FATTR4_WORD0_SIZE)
 		if (xdr_stream_decode_u64(xdr, &fattr->ncf_cb_fsize) < 0)
-			return -NFSERR_BAD_XDR;
+			return -EIO;
 	if (bitmap[2] & FATTR4_WORD2_TIME_DELEG_ACCESS) {
 		fattr4_time_deleg_access access;
 
 		if (!xdrgen_decode_fattr4_time_deleg_access(xdr, &access))
-			return -NFSERR_BAD_XDR;
+			return -EIO;
 		fattr->ncf_cb_atime.tv_sec = access.seconds;
 		fattr->ncf_cb_atime.tv_nsec = access.nseconds;
 
···
 		fattr4_time_deleg_modify modify;
 
 		if (!xdrgen_decode_fattr4_time_deleg_modify(xdr, &modify))
-			return -NFSERR_BAD_XDR;
+			return -EIO;
 		fattr->ncf_cb_mtime.tv_sec = modify.seconds;
 		fattr->ncf_cb_mtime.tv_nsec = modify.nseconds;
 
···
 	if (unlikely(status || cb->cb_status))
 		return status;
 	if (xdr_stream_decode_uint32_array(xdr, bitmap, 3) < 0)
-		return -NFSERR_BAD_XDR;
+		return -EIO;
 	if (xdr_stream_decode_u32(xdr, &attrlen) < 0)
-		return -NFSERR_BAD_XDR;
+		return -EIO;
 	maxlen = sizeof(ncf->ncf_cb_change) + sizeof(ncf->ncf_cb_fsize);
 	if (bitmap[2] != 0)
 		maxlen += (sizeof(ncf->ncf_cb_mtime.tv_sec) +
 			   sizeof(ncf->ncf_cb_mtime.tv_nsec)) * 2;
 	if (attrlen > maxlen)
-		return -NFSERR_BAD_XDR;
+		return -EIO;
 	status = decode_cb_fattr4(xdr, bitmap, ncf);
 	return status;
 }