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

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Message-ID: <bfc1bab9a8f2f51e19ba4fd57a6b8bdf69683d42.camel@wdc.com>
Date: Thu, 25 Sep 2025 23:37:09 +0000
From: Wilfred Mallawa <wilfred.mallawa@....com>
To: "sd@...asysnail.net" <sd@...asysnail.net>
CC: "corbet@....net" <corbet@....net>, "davem@...emloft.net"
	<davem@...emloft.net>, "linux-kselftest@...r.kernel.org"
	<linux-kselftest@...r.kernel.org>, "john.fastabend@...il.com"
	<john.fastabend@...il.com>, "shuah@...nel.org" <shuah@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"kuba@...nel.org" <kuba@...nel.org>, "pabeni@...hat.com" <pabeni@...hat.com>,
	"edumazet@...gle.com" <edumazet@...gle.com>, "linux-doc@...r.kernel.org"
	<linux-doc@...r.kernel.org>, "horms@...nel.org" <horms@...nel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH v4 1/2] net/tls: support maximum record size limit

On Thu, 2025-09-25 at 23:29 +0200, Sabrina Dubroca wrote:
> 2025-09-25, 05:39:14 +0000, Wilfred Mallawa wrote:
> > On Wed, 2025-09-24 at 19:50 +0200, Sabrina Dubroca wrote:
> > > > @@ -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.
> > Makes sense to keep the behaviour the same as getsockopt() right?
> > So
> > add the +1 changes here based on version (same as getsockopt()). In
> > which case, it should never exceed TLS_MAX_PAYLOAD_SIZE.
> 
> The max value for 1.3 is TLS_MAX_PAYLOAD_SIZE+1 (after adjustment),
> since it's the max value that will be accepted by setsockopt (after
> passing the "value - 1 > TLS_MAX_PAYLOAD_SIZE" check). And it's the
> value most users will see since it's the default.
Ah I see what you mean.  In regards to "but OTOH users may get confused
about seeing a value larger than TLS_MAX_PAYLOAD_SIZE.", do you think
it's sufficient to document TLS_MAX_PAYLOAD_SIZE and specify that for
TLS 1.3 this doesn't include the ContentType byte?

Wilfred