netdev - Re: [PATCH net-next v3 2/6] tls: block decryption when a rekey is pending

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Message-ID: <ZNUh+3EHK+R0/W2a@vergenet.net>
Date: Thu, 10 Aug 2023 19:44:27 +0200
From: Simon Horman <horms@...nel.org>
To: Sabrina Dubroca <sd@...asysnail.net>
Cc: netdev@...r.kernel.org, Vadim Fedorenko <vfedorenko@...ek.ru>,
	Frantisek Krenzelok <fkrenzel@...hat.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Kuniyuki Iwashima <kuniyu@...zon.com>,
	Apoorv Kothari <apoorvko@...zon.com>,
	Boris Pismenny <borisp@...dia.com>,
	John Fastabend <john.fastabend@...il.com>,
	Shuah Khan <shuah@...nel.org>, linux-kselftest@...r.kernel.org,
	Gal Pressman <gal@...dia.com>,
	Marcel Holtmann <marcel@...tmann.org>
Subject: Re: [PATCH net-next v3 2/6] tls: block decryption when a rekey is
 pending

On Wed, Aug 09, 2023 at 02:58:51PM +0200, Sabrina Dubroca wrote:
> When a TLS handshake record carrying a KeyUpdate message is received,
> all subsequent records will be encrypted with a new key. We need to
> stop decrypting incoming records with the old key, and wait until
> userspace provides a new key.
> 
> Make a note of this in the RX context just after decrypting that
> record, and stop recvmsg/splice calls with EKEYEXPIRED until the new
> key is available.
> 
> v3:
>  - move key_update_pending check into tls_rx_rec_wait (Jakub)
>  - TLS_RECORD_TYPE_HANDSHAKE was added to include/net/tls_prot.h by
>    the tls handshake series, drop that from this patch
>  - move key_update_pending into an existing hole
> 
> Signed-off-by: Sabrina Dubroca <sd@...asysnail.net>
> ---
>  include/net/tls.h |  3 +++
>  net/tls/tls_sw.c  | 36 ++++++++++++++++++++++++++++++++++++
>  2 files changed, 39 insertions(+)
> 
> diff --git a/include/net/tls.h b/include/net/tls.h
> index 06fca9160346..219a4f38c0e4 100644
> --- a/include/net/tls.h
> +++ b/include/net/tls.h
> @@ -69,6 +69,8 @@ extern const struct tls_cipher_size_desc tls_cipher_size_desc[];
>  
>  #define TLS_CRYPTO_INFO_READY(info)	((info)->cipher_type)
>  
> +#define TLS_HANDSHAKE_KEYUPDATE		24	/* rfc8446 B.3: Key update */
> +
>  #define TLS_AAD_SPACE_SIZE		13
>  
>  #define MAX_IV_SIZE			16
> @@ -141,6 +143,7 @@ struct tls_sw_context_rx {
>  	u8 async_capable:1;
>  	u8 zc_capable:1;
>  	u8 reader_contended:1;
> +	bool key_update_pending;

Hi Sabrina,

Would it make sense for this to be

	u8 key_update_pending:1;

>  
>  	struct tls_strparser strp;
>  
> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c
> index 2ca0eb90a2a5..497f56c5f169 100644
> --- a/net/tls/tls_sw.c
> +++ b/net/tls/tls_sw.c
> @@ -1293,6 +1293,10 @@ tls_rx_rec_wait(struct sock *sk, struct sk_psock *psock, bool nonblock,
>  	DEFINE_WAIT_FUNC(wait, woken_wake_function);
>  	long timeo;
>  
> +	/* a rekey is pending, let userspace deal with it */
> +	if (unlikely(ctx->key_update_pending))
> +		return -EKEYEXPIRED;
> +
>  	timeo = sock_rcvtimeo(sk, nonblock);
>  
>  	while (!tls_strp_msg_ready(ctx)) {
> @@ -1689,6 +1693,33 @@ tls_decrypt_device(struct sock *sk, struct msghdr *msg,
>  	return 1;
>  }
>  
> +static int tls_check_pending_rekey(struct sock *sk, struct sk_buff *skb)
> +{
> +	const struct tls_msg *tlm = tls_msg(skb);
> +	const struct strp_msg *rxm = strp_msg(skb);

nit: reverse xmas tree

> +
> +	if (tlm->control == TLS_RECORD_TYPE_HANDSHAKE) {
> +		char hs_type;
> +		int err;
> +
> +		if (rxm->full_len < 1)
> +			return -EINVAL;
> +
> +		err = skb_copy_bits(skb, rxm->offset, &hs_type, 1);
> +		if (err < 0)
> +			return err;
> +
> +		if (hs_type == TLS_HANDSHAKE_KEYUPDATE) {
> +			struct tls_context *ctx = tls_get_ctx(sk);
> +			struct tls_sw_context_rx *rx_ctx = ctx->priv_ctx_rx;
> +
> +			rx_ctx->key_update_pending = true;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static int tls_rx_one_record(struct sock *sk, struct msghdr *msg,
>  			     struct tls_decrypt_arg *darg)
>  {
> @@ -1708,6 +1739,10 @@ static int tls_rx_one_record(struct sock *sk, struct msghdr *msg,
>  	rxm->full_len -= prot->overhead_size;
>  	tls_advance_record_sn(sk, prot, &tls_ctx->rx);
>  
> +	err = tls_check_pending_rekey(sk, darg->skb);
> +	if (err < 0)
> +		return err;
> +
>  	return 0;
>  }
>  
> @@ -2642,6 +2677,7 @@ int tls_set_sw_offload(struct sock *sk, int tx)
>  		skb_queue_head_init(&sw_ctx_rx->rx_list);
>  		skb_queue_head_init(&sw_ctx_rx->async_hold);
>  		aead = &sw_ctx_rx->aead_recv;
> +		sw_ctx_rx->key_update_pending = false;
>  	}
>  
>  	switch (crypto_info->cipher_type) {
> -- 
> 2.40.1
> 
>