netdev - Re: [PATCH net-next v8 1/2] net/tls: support setting the maximum payload size

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Message-ID: <20251024163336.5fba5cd1@kernel.org>
Date: Fri, 24 Oct 2025 16:33:36 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Wilfred Mallawa <wilfred.opensource@...il.com>
Cc: Sabrina Dubroca <sd@...asysnail.net>, netdev@...r.kernel.org,
 linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Jonathan Corbet	 <corbet@....net>, Simon Horman <horms@...nel.org>, John
 Fastabend	 <john.fastabend@...il.com>, Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH net-next v8 1/2] net/tls: support setting the maximum
 payload size

On Fri, 24 Oct 2025 12:11:11 +1000 Wilfred Mallawa wrote:
> In the previous record_size_limit approach for TLS 1.3, we need to
> account for the ContentType byte. Which complicates get/setsockopt()
> and tls_get_info(), where in setsockopt() for TLS 1.3 we need to
> subtract 1 to the user provided value and in getsockopt() we need add 1
> to keep the symmetry between the two (similarly in tls_get_info()). The
> underlying assumption was that userspace passes up directly what the
> endpoint specified as the record_size_limit.
> 
> With this approach we don't need to worry about it and we can pass the
> responsibility to user-space as documented, which I think makes the
> kernel code simpler.

But we haven't managed to avoid that completely:

+	if (value < TLS_MIN_RECORD_SIZE_LIM - (tls_13 ? 1 : 0) ||

I understand the motivation, the kernel code is indeed simpler.

Last night I read the RFC and then this patch, and it took me like
10min to get all of it straight in my head. Maybe I was tried but
I feel like the user space developers will judge us harshly for 
the current uAPI.