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

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Message-ID: <aNmsTxyg75HHkmIJ@krikkit>
Date: Sun, 28 Sep 2025 23:44:47 +0200
From: Sabrina Dubroca <sd@...asysnail.net>
To: Wilfred Mallawa <wilfred.mallawa@....com>,
	"kuba@...nel.org" <kuba@...nel.org>
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>,
	"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

2025-09-25, 23:37:09 +0000, Wilfred Mallawa wrote:
> 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?

I guess it will have to do. Otherwise, unless someone has another
idea, we're back to the discussion on v3 (ie setting the actual
payload size instead of the record limit).

-- 
Sabrina