RE: [PATCH bpf-next v4 1/5] bpf: Add bpf_link support for sk_msg and sk_skb progs

[John Fastabend <john.fastabend@gmail.com>]

Yonghong Song wrote:
> Add bpf_link support for sk_msg and sk_skb programs. We have an
> internal request to support bpf_link for sk_msg programs so user
> space can have a uniform handling with bpf_link based libbpf
> APIs. Using bpf_link based libbpf API also has a benefit which
> makes system robust by decoupling prog life cycle and
> attachment life cycle.
> 
> Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
> ---
>  include/linux/bpf.h            |   6 +
>  include/linux/skmsg.h          |   4 +
>  include/uapi/linux/bpf.h       |   5 +
>  kernel/bpf/syscall.c           |   4 +
>  net/core/sock_map.c            | 268 ++++++++++++++++++++++++++++++++-
>  tools/include/uapi/linux/bpf.h |   5 +
>  6 files changed, 284 insertions(+), 8 deletions(-)
> 

LGTM one question below.

> +/* Handle the following two cases:
> + * case 1: link != NULL, prog != NULL, old != NULL
> + * case 2: link != NULL, prog != NULL, old == NULL
> + */
> +static int sock_map_link_update_prog(struct bpf_link *link,
> +				     struct bpf_prog *prog,
> +				     struct bpf_prog *old)
> +{
> +	const struct sockmap_link *sockmap_link = container_of(link, struct sockmap_link, link);
> +	struct bpf_prog **pprog;
> +	struct bpf_link **plink;
> +	int ret = 0;
> +
> +	mutex_lock(&sockmap_mutex);
> +
> +	/* If old prog is not NULL, ensure old prog is the same as link->prog. */
> +	if (old && link->prog != old) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +	/* Ensure link->prog has the same type/attach_type as the new prog. */
> +	if (link->prog->type != prog->type ||
> +	    link->prog->expected_attach_type != prog->expected_attach_type) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	ret = sock_map_prog_lookup(sockmap_link->map, &pprog,
> +				   sockmap_link->attach_type);
> +	if (ret)
> +		goto out;
> +
> +	/* Ensure the same link between the one in map and the passed-in. */
> +	ret = sock_map_link_lookup(sockmap_link->map, &plink, link, false,
> +				   sockmap_link->attach_type);
> +	if (ret)
> +		goto out;
> +
> +	if (old) {
> +		ret = psock_replace_prog(pprog, prog, old);
> +		goto out;
> +	}
> +
> +	psock_set_prog(pprog, prog);
> +
> +out:
> +	if (!ret) {
> +		bpf_prog_inc(prog);
> +		old = xchg(&link->prog, prog);
> +		bpf_prog_put(old);

Need to check old? I don't think we can clal bpf_prog_put on null?

  if (old)
     bpf_prog_put(old)

> +	}
> +	mutex_unlock(&sockmap_mutex);
> +	return ret;
> +}
> +