netdev - Re: [PATCH net-next 0/5] tls: implement key updates for TLS1.3

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Date:   Thu, 19 Jan 2023 11:27:49 +0200
From:   Gal Pressman <gal@...dia.com>
To:     Jakub Kicinski <kuba@...nel.org>,
        Sabrina Dubroca <sd@...asysnail.net>,
        Tariq Toukan <tariqt@...dia.com>,
        Boris Pismenny <borisp@...dia.com>
Cc:     netdev@...r.kernel.org, Frantisek Krenzelok <fkrenzel@...hat.com>
Subject: Re: [PATCH net-next 0/5] tls: implement key updates for TLS1.3

On 19/01/2023 4:55, Jakub Kicinski wrote:
> On Wed, 18 Jan 2023 11:06:25 +0100 Sabrina Dubroca wrote:
>> 2023-01-17, 18:03:51 -0800, Jakub Kicinski wrote:
>>> On Tue, 17 Jan 2023 14:45:26 +0100 Sabrina Dubroca wrote:  
>>>> This adds support for receiving KeyUpdate messages (RFC 8446, 4.6.3
>>>> [1]). A sender transmits a KeyUpdate message and then changes its TX
>>>> key. The receiver should react by updating its RX key before
>>>> processing the next message.
>>>>
>>>> This patchset implements key updates by:
>>>>  1. pausing decryption when a KeyUpdate message is received, to avoid
>>>>     attempting to use the old key to decrypt a record encrypted with
>>>>     the new key
>>>>  2. returning -EKEYEXPIRED to syscalls that cannot receive the
>>>>     KeyUpdate message, until the rekey has been performed by userspace  
>>>
>>> Why? We return to user space after hitting a cmsg, don't we?
>>> If the user space wants to keep reading with the old key - 🤷️  
>>
>> But they won't be able to read anything. Either we don't pause
>> decryption, and the socket is just broken when we look at the next
>> record, or we pause, and there's nothing to read until the rekey is
>> done. I think that -EKEYEXPIRED is better than breaking the socket
>> just because a read snuck in between getting the cmsg and setting the
>> new key.
> 
> IDK, we don't interpret any other content types/cmsgs, and for well
> behaved user space there should be no problem (right?).
> I'm weakly against, if nobody agrees with me you can keep as is.
> 
>>>>  3. passing the KeyUpdate message to userspace as a control message
>>>>  4. allowing updates of the crypto_info via the TLS_TX/TLS_RX
>>>>     setsockopts
>>>>
>>>> This API has been tested with gnutls to make sure that it allows
>>>> userspace libraries to implement key updates [2]. Thanks to Frantisek
>>>> Krenzelok <fkrenzel@...hat.com> for providing the implementation in
>>>> gnutls and testing the kernel patches.  
>>>
>>> Please explain why - the kernel TLS is not faster than user space, 
>>> the point of it is primarily to enable offload. And you don't add
>>> offload support here.  
>>
>> Well, TLS1.3 support was added 4 years ago, and yet the offload still
>> doesn't support 1.3 at all.
> 
> I'm pretty sure some devices support it. None of the vendors could 
> be bothered to plumb in the kernel support, yet, tho.

Our device supports TLS 1.3, it's in our plans to add driver/kernel support.

> I don't know of anyone supporting rekeying.

Boris, Tariq, do you know?