Re: [RFC PATCH 1/4] bpf: add new prog_type BPF_PROG_TYPE_IO_FILTER

[Jakub Sitnicki <jakub@cloudflare.com>]

On Wed, Aug 12, 2020 at 06:33 PM CEST, Leah Rumancik wrote:
> Introducing a new program type BPF_PROG_TYPE_IO_FILTER and a new
> attach type BPF_BIO_SUBMIT.
>
> This program type is intended to help filter and monitor IO requests.
>
> Co-developed-by: Saranya Muruganandam <saranyamohan@google.com>
> Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>
> Signed-off-by: Kjetil Ørbekk <orbekk@google.com>
> Signed-off-by: Harshad Shirwadkar <harshads@google.com>
> Signed-off-by: Leah Rumancik <leah.rumancik@gmail.com>
> ---

[...]

> diff --git a/block/blk-bpf-io-filter.c b/block/blk-bpf-io-filter.c
> new file mode 100644
> index 000000000000..453d6b156bd2
> --- /dev/null
> +++ b/block/blk-bpf-io-filter.c

[...]

> +int io_filter_prog_attach(const union bpf_attr *attr, struct bpf_prog *prog)
> +{
> +	struct gendisk *disk;
> +	struct fd f;
> +	struct bpf_prog_array *old_array;
> +	struct bpf_prog_array *new_array;
> +	int ret;
> +
> +	if (attr->attach_flags)
> +		return -EINVAL;
> +
> +	f = fdget(attr->target_fd);
            ^^^^^

Missing corresponding fdput?

As per Martin's suggestion, with bpf_link this will become the
link_create callback, but the comment still stands.

> +	if (!f.file)
> +		return -EBADF;
> +
> +	disk = I_BDEV(f.file->f_mapping->host)->bd_disk;
> +	if (disk == NULL)
> +		return -ENXIO;
> +
> +	ret = mutex_lock_interruptible(&disk->io_filter_lock);
> +	if (ret)
> +		return ret;
> +
> +	old_array = io_filter_rcu_dereference_progs(disk);
> +	if (old_array && bpf_prog_array_length(old_array) >= BPF_MAX_PROGS) {
> +		ret = -E2BIG;
> +		goto unlock;
> +	}
> +
> +	ret = bpf_prog_array_copy(old_array, NULL, prog, &new_array);
> +	if (ret < 0)
> +		goto unlock;
> +
> +	rcu_assign_pointer(disk->progs, new_array);
> +	bpf_prog_array_free(old_array);
> +
> +unlock:
> +	mutex_unlock(&disk->io_filter_lock);
> +	return ret;
> +}

[...]