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

[Antonio Quartulli <antonio@openvpn.net>]

On 01/04/2025 11:59, Sabrina Dubroca wrote:
> 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.

Oh right - this comment can go.

> 
>> +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.

Right!
This code flow was re-arranged a couple of times, and I have missed that 
we now always hit those free()s in post().

I prefer to drop them and put a comment indicating that cleanup happens 
in post().

> 
> (same thing on the decrypt side)

Yep

> 
>> +	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 :(

ACK!

> 
>> + *
>> + * 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);
>> +}
> 

Regards,

-- 
Antonio Quartulli
OpenVPN Inc.