nvmet_check_data_len() wrong behavior for nvme admin set features cmd

[Engel, Amit]

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

If you agree with us, we will submit a patch with this change

Thanks,
Amit E