linux-kernel - Re: [PATCH v4 1/2] net/tls: support maximum record size limit

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Message-ID: <aNQvgD7AvFe7-sAv@krikkit>
Date: Wed, 24 Sep 2025 19:50:56 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Wilfred Mallawa <wilfred.opensource@...il.com>
Cc: netdev@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, horms@...nel.org, corbet@....net,
	john.fastabend@...il.com, shuah@...nel.org,
	Wilfred Mallawa <wilfred.mallawa@....com>
Subject: Re: [PATCH v4 1/2] net/tls: support maximum record size limit

2025-09-23, 15:32:06 +1000, Wilfred Mallawa wrote:
> diff --git a/net/tls/tls_main.c b/net/tls/tls_main.c
> index a3ccb3135e51..09883d9c6c96 100644
> --- a/net/tls/tls_main.c
> +++ b/net/tls/tls_main.c
> @@ -544,6 +544,31 @@ static int do_tls_getsockopt_no_pad(struct sock *sk, char __user *optval,
>  	return 0;
>  }
>  
> +static int do_tls_getsockopt_tx_record_size(struct sock *sk, char __user *optval,
> +					    int __user *optlen)
> +{
> +	struct tls_context *ctx = tls_get_ctx(sk);
> +	int len;
> +	/* TLS 1.3: Record length contains ContentType */
> +	u16 record_size_limit = ctx->prot_info.version == TLS_1_3_VERSION ?
> +				ctx->tx_record_size_limit + 1 :
> +				ctx->tx_record_size_limit;

nit: reverse xmas tree


[...]
> +static int do_tls_setsockopt_tx_record_size(struct sock *sk, sockptr_t optval,
> +					    unsigned int optlen)
> +{
> +	struct tls_context *ctx = tls_get_ctx(sk);
> +	struct tls_sw_context_tx *sw_ctx = tls_sw_ctx_tx(ctx);
> +	u16 value;
> +
> +	if (sw_ctx->open_rec)
> +		return -EBUSY;
> +
> +	if (sockptr_is_null(optval) || optlen != sizeof(value))
> +		return -EINVAL;
> +
> +	if (copy_from_sockptr(&value, optval, sizeof(value)))
> +		return -EFAULT;
> +
> +	if (value < TLS_MIN_RECORD_SIZE_LIM)
> +		return -EINVAL;
> +
> +	if (ctx->prot_info.version == TLS_1_2_VERSION &&
> +	    value > TLS_MAX_PAYLOAD_SIZE)
> +		return -EINVAL;
> +
> +	if (ctx->prot_info.version == TLS_1_3_VERSION &&
> +	    value - 1 > TLS_MAX_PAYLOAD_SIZE)
> +		return -EINVAL;
> +
> +	/*
> +	 * For TLS 1.3: 'value' includes one byte for the appended ContentType.
> +	 * Adjust the kernel's internal plaintext limit accordingly.
> +	 */
> +	ctx->tx_record_size_limit = ctx->prot_info.version == TLS_1_3_VERSION ?
> +				    value - 1 : value;
> +
> +	return 0;
> +}
> +
>  static int do_tls_setsockopt(struct sock *sk, int optname, sockptr_t optval,
>  			     unsigned int optlen)
>  {
> @@ -833,6 +898,9 @@ static int do_tls_setsockopt(struct sock *sk, int optname, sockptr_t optval,
>  	case TLS_RX_EXPECT_NO_PAD:
>  		rc = do_tls_setsockopt_no_pad(sk, optval, optlen);
>  		break;
> +	case TLS_TX_RECORD_SIZE_LIM:
> +		rc = do_tls_setsockopt_tx_record_size(sk, optval, optlen);

I think we want to lock the socket here, to avoid any concurrent send()?
Especially now with the ->open_rec check.


> @@ -1111,6 +1180,11 @@ static int tls_get_info(struct sock *sk, struct sk_buff *skb, bool net_admin)
>  			goto nla_failure;
>  	}
>  
> +	err = nla_put_u16(skb, TLS_INFO_TX_RECORD_SIZE_LIM,
> +			  ctx->tx_record_size_limit);

I'm not sure here: if we do the +1 adjustment we'd be consistent with
the value reported by getsockopt, but OTOH users may get confused
about seeing a value larger than TLS_MAX_PAYLOAD_SIZE.

-- 
Sabrina