Re: [PATCH v2 5/8] ib_uverbs: Add padding to end align ib_uverbs_reg_mr_resp

[Yishai Hadas <yishaih@dev.mellanox.co.il>]

On 9/16/2016 9:31 PM, Knut Omang wrote:
> The ib_uverbs_reg_mr_resp structure was not 64 bit end aligned
> as required by the protocol. This causes alignment issues
> if a device specific driver needs to transfer extra response
> arguments.
>
> Avoid breaking backward compatibility by improving the handling
> of the length checking in ib_uverbs_reg_mr to consider the case
> where the kernel has been updated, but user space still has
> the old length without padding.
>
> Signed-off-by: Knut Omang <knut.omang@oracle.com>
> ---
>  drivers/infiniband/core/uverbs_cmd.c | 10 ++++++----
>  include/uapi/rdma/ib_user_verbs.h    |  1 +
>  2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/infiniband/core/uverbs_cmd.c b/drivers/infiniband/core/uverbs_cmd.c
> index dbc5885..fa8a717 100644
> --- a/drivers/infiniband/core/uverbs_cmd.c
> +++ b/drivers/infiniband/core/uverbs_cmd.c
> @@ -967,16 +967,18 @@ ssize_t ib_uverbs_reg_mr(struct ib_uverbs_file *file,
>  	struct ib_pd                *pd;
>  	struct ib_mr                *mr;
>  	int                          ret;
> +	size_t resp_size = sizeof resp;
>
> -	if (out_len < sizeof resp)
> -		return -ENOSPC;
> +	if (out_len < resp_size) {
> +		resp_size = out_len;
> +	}

You don't preserve the minimum response size error checking in your code 
(i.e  -ENOSPC). We can expect an error if outlen is less than the
offset of rkey in ib_uverbs_reg_mr_resp.

Please note that below call to copy_to_user will succeed as it copies 
now based on resp_size and won't return the basic mandatory output.


>  	if (copy_from_user(&cmd, buf, sizeof cmd))
>  		return -EFAULT;
>
>  	INIT_UDATA(&udata, buf + sizeof cmd,
>  		   (unsigned long) cmd.response + sizeof resp,
> -		   in_len - sizeof cmd, out_len - sizeof resp);
> +		   in_len - sizeof cmd, out_len - resp_size);
>
>  	if ((cmd.start & ~PAGE_MASK) != (cmd.hca_va & ~PAGE_MASK))
>  		return -EINVAL;
> @@ -1030,7 +1032,7 @@ ssize_t ib_uverbs_reg_mr(struct ib_uverbs_file *file,
>  	resp.mr_handle = uobj->id;
>
>  	if (copy_to_user((void __user *) (unsigned long) cmd.response,
> -			 &resp, sizeof resp)) {
> +			 &resp, resp_size)) {
>  		ret = -EFAULT;
>  		goto err_copy;
>  	}
> diff --git a/include/uapi/rdma/ib_user_verbs.h b/include/uapi/rdma/ib_user_verbs.h
> index 7f035f4..6b8c9c0 100644
> --- a/include/uapi/rdma/ib_user_verbs.h
> +++ b/include/uapi/rdma/ib_user_verbs.h
> @@ -307,6 +307,7 @@ struct ib_uverbs_reg_mr_resp {
>  	__u32 mr_handle;
>  	__u32 lkey;
>  	__u32 rkey;
> +	__u32 reserved;
>  };
>
>  struct ib_uverbs_rereg_mr {
>