Re: [PATCH net-next v2 09/22] ovpn: implement basic RX path (UDP)

[Simon Horman <horms@kernel.org>]

On Mon, Mar 04, 2024 at 04:09:00PM +0100, Antonio Quartulli wrote:
> Packets received over the socket are forwarded to the user device.
> 
> Impementation is UDP only. TCP will be added by a later patch.

nit: Implementation

> 
> Note: no decryption/decapsulation exists yet, packets are forwarded as
> they arrive without much processing.
> 
> Signed-off-by: Antonio Quartulli <antonio@openvpn.net>

...

> diff --git a/drivers/net/ovpn/proto.h b/drivers/net/ovpn/proto.h
> new file mode 100644
> index 000000000000..c016422fe6f3
> --- /dev/null
> +++ b/drivers/net/ovpn/proto.h
> @@ -0,0 +1,101 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*  OpenVPN data channel offload
> + *
> + *  Copyright (C) 2020-2024 OpenVPN, Inc.
> + *
> + *  Author:	Antonio Quartulli <antonio@openvpn.net>
> + *		James Yonan <james@openvpn.net>
> + */
> +
> +#ifndef _NET_OVPN_OVPNPROTO_H_
> +#define _NET_OVPN_OVPNPROTO_H_
> +
> +#include "main.h"
> +
> +#include <linux/skbuff.h>
> +
> +/* Methods for operating on the initial command
> + * byte of the OpenVPN protocol.
> + */
> +
> +/* packet opcode (high 5 bits) and key-id (low 3 bits) are combined in
> + * one byte
> + */
> +#define OVPN_KEY_ID_MASK 0x07
> +#define OVPN_OPCODE_SHIFT 3
> +#define OVPN_OPCODE_MASK 0x1F
> +/* upper bounds on opcode and key ID */
> +#define OVPN_KEY_ID_MAX (OVPN_KEY_ID_MASK + 1)
> +#define OVPN_OPCODE_MAX (OVPN_OPCODE_MASK + 1)
> +/* packet opcodes of interest to us */
> +#define OVPN_DATA_V1 6 /* data channel V1 packet */
> +#define OVPN_DATA_V2 9 /* data channel V2 packet */
> +/* size of initial packet opcode */
> +#define OVPN_OP_SIZE_V1 1
> +#define OVPN_OP_SIZE_V2	4
> +#define OVPN_PEER_ID_MASK 0x00FFFFFF
> +#define OVPN_PEER_ID_UNDEF 0x00FFFFFF
> +/* first byte of keepalive message */
> +#define OVPN_KEEPALIVE_FIRST_BYTE 0x2a
> +/* first byte of exit message */
> +#define OVPN_EXPLICIT_EXIT_NOTIFY_FIRST_BYTE 0x28
> +
> +/**
> + * Extract the OP code from the specified byte
> + *
> + * Return the OP code
> + */

nit: '/**' denotes the start of a Kernel doc, however,
     other than that syntax this is not a Kernel doc.

     Likewise below.

     Flagged by /scripts/kernel-doc -none

> +static inline u8 ovpn_opcode_from_byte(u8 byte)
> +{
> +	return byte >> OVPN_OPCODE_SHIFT;
> +}
> +
> +/**
> + * Extract the OP code from the skb head.
> + *
> + * Note: this function assumes that the skb head was pulled enough
> + * to access the first byte.
> + *
> + * Return the OP code
> + */
> +static inline u8 ovpn_opcode_from_skb(const struct sk_buff *skb, u16 offset)
> +{
> +	return ovpn_opcode_from_byte(*(skb->data + offset));
> +}
> +
> +/**
> + * Extract the key ID from the skb head.
> + *
> + * Note: this function assumes that the skb head was pulled enough
> + * to access the first byte.
> + *
> + * Return the key ID
> + */
> +
> +static inline u8 ovpn_key_id_from_skb(const struct sk_buff *skb)
> +{
> +	return *skb->data & OVPN_KEY_ID_MASK;
> +}
> +
> +/**
> + * Extract the peer ID from the skb head.
> + *
> + * Note: this function assumes that the skb head was pulled enough
> + * to access the first 4 bytes.
> + *
> + * Return the peer ID.
> + */
> +
> +static inline u32 ovpn_peer_id_from_skb(const struct sk_buff *skb, u16 offset)
> +{
> +	return ntohl(*(__be32 *)(skb->data + offset)) & OVPN_PEER_ID_MASK;
> +}
> +
> +static inline u32 ovpn_opcode_compose(u8 opcode, u8 key_id, u32 peer_id)
> +{
> +	const u8 op = (opcode << OVPN_OPCODE_SHIFT) | (key_id & OVPN_KEY_ID_MASK);
> +
> +	return (op << 24) | (peer_id & OVPN_PEER_ID_MASK);
> +}
> +
> +#endif /* _NET_OVPN_OVPNPROTO_H_ */

...