nvmet_check_data_len() wrong behavior for nvme admin set features cmd

[Sagi Grimberg]

> Hi Sagi et al.
> 
> We see a wrong behaviour in nvmet/core.c  nvmet_check_data_len() function for nvme admin set_features command:
> Current nvmet_check_data_len() code is checking if data_len != req->transfer_len.
> 
> There are some feature ids which the transfer_len that is being sent by the host is larger than the payload itself.
> For example:
> fid 0xE, the data_len that is sent by the host is 8.
> fid 0xC, the data_len that is sent by the host is 256.
> 
> In this case, the error that is returned to the host is ‘NVME_SC_SGL_INVALID_DATA | NVME_SC_DNR’, which is not accurate.
>  From our understanding, the host is allowed to send sgl describing a beffer that is larger than the payload.
> 
> We thought to change the condition in nvmet_check_data_len() to check if ‘data_len > req->transfer_len’.
> Only in this case, the expected status code is Indeed NVME_SC_SGL_INVALID_DATA | NVME_SC_DNR

We already have a handle for that in nvmet_check_data_len_lte() that is
used by dsm handlers, it should be added to the specific places where
it is appropriate.