Re: [PATCH 03/10] RDMA: Add ib_respond_udata()

[Leon Romanovsky <leon@kernel.org>]

On Thu, Feb 05, 2026 at 09:45:37PM -0400, Jason Gunthorpe wrote:
> Wrap the common copy_to_user() pattern used in drivers and enhance it
> to zero pad as well.
> 
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> ---
>  include/rdma/ib_verbs.h | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/include/rdma/ib_verbs.h b/include/rdma/ib_verbs.h
> index bb61cab2ef9a06..c0dd82a77e7a13 100644
> --- a/include/rdma/ib_verbs.h
> +++ b/include/rdma/ib_verbs.h
> @@ -3177,6 +3177,38 @@ static inline int _ib_copy_validate_udata_in(struct ib_udata *udata, void *req,
>  		ret;                                                          \
>  	})
>  
> +static inline int _ib_respond_udata(struct ib_udata *udata, const void *src,
> +				   size_t len)
> +{
> +	size_t copy_len;
> +
> +	copy_len = min(len, udata->outlen);

Don't you need to check that udata->outlen is larger than zero?

Thanks

> +	if (copy_to_user(udata->outbuf, src, copy_len))
> +		return -EFAULT;
> +	if (copy_len < udata->outlen) {
> +		if (clear_user(udata->outbuf + copy_len,
> +			       udata->outlen - copy_len))
> +			return -EFAULT;
> +	}
> +	return 0;
> +}
> +
> +/**
> + * ib_respond_udata - Copy a driver data response to userspace
> + * @_udata: The system calls ib_udata struct
> + * @_rep: Kernel buffer containing the response driver data on the stack
> + *
> + * Copy driver data response structures back to userspace in a way that
> + * is forwards and backwards compatible. Longer kernel structs are truncated,
> + * userspace has made some kind of error if it needed the truncated information.
> + * Shorter structs are zero padded.
> + */
> +#define ib_respond_udata(_udata, _rep)                                   \
> +	({                                                               \
> +		static_assert(__same_type(*(typeof(&(_rep)))0, (_rep))); \
> +		_ib_respond_udata(_udata, &(_rep), sizeof(_rep));        \
> +	})
> +
>  /**
>   * ib_modify_qp_is_ok - Check that the supplied attribute mask
>   * contains all required attributes and no attributes not allowed for
> -- 
> 2.43.0
> 
>