linux-kernel - Re: [PATCH v21 09/24] ovpn: implement packet processing

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Message-ID: <Z8dOOy9tSpJ1UCiR@hog>
Date: Tue, 4 Mar 2025 20:02:19 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: Antonio Quartulli <antonio@...nvpn.net>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Donald Hunter <donald.hunter@...il.com>,
	Shuah Khan <shuah@...nel.org>, ryazanov.s.a@...il.com,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, Xiao Liang <shaw.leon@...il.com>
Subject: Re: [PATCH v21 09/24] ovpn: implement packet processing

2025-03-04, 01:33:39 +0100, Antonio Quartulli wrote:
> +struct crypto_aead *ovpn_aead_init(const char *title, const char *alg_name,
> +				   const unsigned char *key,
> +				   unsigned int keylen)

nit: static? I don't see it used outside this file.


[...]
> +static inline struct ovpn_crypto_key_slot *
> +ovpn_crypto_key_id_to_slot(const struct ovpn_crypto_state *cs, u8 key_id)
> +{
> +	struct ovpn_crypto_key_slot *ks;
> +	u8 idx;
> +
> +	if (unlikely(!cs))
> +		return NULL;
> +
> +	rcu_read_lock();
> +	idx = cs->primary_idx;

I'd go with slots[0] and slots[1], since it doesn't really matter
whether we check the primary or secondary first. It would avoid a
possible reload of cs->primary_idx (which might be updated
concurrently by a key swap and cause us to look into the same slot
twice) -- a READ_ONCE would also prevent that.

> +	ks = rcu_dereference(cs->slots[idx]);
> +	if (ks && ks->key_id == key_id) {
> +		if (unlikely(!ovpn_crypto_key_slot_hold(ks)))
> +			ks = NULL;
> +		goto out;
> +	}
> +
> +	ks = rcu_dereference(cs->slots[!idx]);
> +	if (ks && ks->key_id == key_id) {
> +		if (unlikely(!ovpn_crypto_key_slot_hold(ks)))
> +			ks = NULL;
> +		goto out;
> +	}
> +
> +	/* when both key slots are occupied but no matching key ID is found, ks
> +	 * has to be reset to NULL to avoid carrying a stale pointer
> +	 */
> +	ks = NULL;
> +out:
> +	rcu_read_unlock();
> +
> +	return ks;
> +}

-- 
Sabrina