Re: [PATCH net-next v24 09/23] ovpn: implement packet processing

[Sabrina Dubroca <sd@queasysnail.net>]

2025-03-18, 02:40:44 +0100, Antonio Quartulli wrote:
> +/* this swap is not atomic, but there will be a very short time frame where the
> + * old_secondary key won't be available. This should not be a big deal as most
> + * likely both peers are already using the new primary at this point.
> + */

This is not the case anymore.

> +void ovpn_crypto_key_slots_swap(struct ovpn_crypto_state *cs)
> +{
> +	const struct ovpn_crypto_key_slot *old_primary, *old_secondary;
> +	u8 idx;
> +
> +	spin_lock_bh(&cs->lock);
> +	idx = cs->primary_idx;
> +	old_primary = rcu_dereference_protected(cs->slots[idx],
> +						lockdep_is_held(&cs->lock));
> +	old_secondary = rcu_dereference_protected(cs->slots[!idx],
> +						  lockdep_is_held(&cs->lock));
> +	/* perform real swap by switching the index of the primary key */
> +	WRITE_ONCE(cs->primary_idx, !cs->primary_idx);
> +
> +	pr_debug("key swapped: (old primary) %d <-> (new primary) %d\n",
> +		 old_primary ? old_primary->key_id : -1,
> +		 old_secondary ? old_secondary->key_id : -1);
> +
> +	spin_unlock_bh(&cs->lock);
> +}

[...]
> +int ovpn_aead_encrypt(struct ovpn_peer *peer, struct ovpn_crypto_key_slot *ks,
> +		      struct sk_buff *skb)
> +{
[...]
> +	/* encrypt it */
> +	return crypto_aead_encrypt(req);
> +free_iv:
> +	kfree(ovpn_skb_cb(skb)->iv);
> +	ovpn_skb_cb(skb)->iv = NULL;
> +free_sg:
> +	kfree(ovpn_skb_cb(skb)->sg);
> +	ovpn_skb_cb(skb)->sg = NULL;

nit: Those shouldn't really be needed, since we'll call
ovpn_encrypt_post that will take care of iv/sg/req. But it's fine if
you leave them.

(same thing on the decrypt side)

> +	return ret;
> +}


[...]
> +/**
> + * ovpn_key_id_from_skb - extract key ID from the skb head
> + * @skb: the packet to extract the key ID code from
> + *
> + * Note: this function assumes that the skb head was pulled enough
> + * to access the first byte.

nit: another "first byte" that I missed previously :(

> + *
> + * Return: the key ID
> + */
> +static inline u8 ovpn_key_id_from_skb(const struct sk_buff *skb)
> +{
> +	u32 opcode = be32_to_cpu(*(__be32 *)skb->data);
> +
> +	return FIELD_GET(OVPN_OPCODE_KEYID_MASK, opcode);
> +}

-- 
Sabrina