Re: [PATCH net-next v4 1/6] tls: block decryption when a rekey is pending

Hi,

On 14/11/24 9:20 pm, Sabrina Dubroca wrote:

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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.

key_update_pending can't be combined with the existing bitfield, because we will read it locklessly in ->poll.

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

v4:

• flip TLS_RECORD_TYPE_HANDSHAKE test and use likely() (Jakub)
• pass ctx rather than sk to tls_check_pending_rekey (Jakub)
• use WRITE_ONCE to set key_update_pending to pair with ->poll's lockless read

Signed-off-by: Sabrina Dubroca sd@queasysnail.net

include/net/tls.h | 3 +++ net/tls/tls_sw.c | 35 +++++++++++++++++++++++++++++++++++ 2 files changed, 38 insertions(+)

diff --git a/include/net/tls.h b/include/net/tls.h index 3a33924db2bc..870e4421c599 100644 --- a/include/net/tls.h +++ b/include/net/tls.h @@ -59,6 +59,8 @@ struct tls_rec;

#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 TLS_MAX_IV_SIZE 16

@@ -130,6 +132,7 @@ struct tls_sw_context_rx { u8 async_capable:1; u8 zc_capable:1; u8 reader_contended:1;

•   bool key_update_pending;
  
     struct tls_strparser strp;
  
  

diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c index bbf26cc4f6ee..db98710c4810 100644 --- a/net/tls/tls_sw.c +++ b/net/tls/tls_sw.c @@ -1314,6 +1314,10 @@ tls_rx_rec_wait(struct sock *sk, struct sk_psock *psock, bool nonblock, int ret = 0; 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)) {
  

@@ -1720,6 +1724,32 @@ tls_decrypt_device(struct sock *sk, struct msghdr *msg, return 1; }

+static int tls_check_pending_rekey(struct tls_context *ctx, struct sk_buff *skb) +{

•   const struct tls_msg *tlm = tls_msg(skb);
  

•   const struct strp_msg *rxm = strp_msg(skb);
  

Missing reverse xmas tree format.

•   char hs_type;
  

•   int err;
  

•   if (likely(tlm->control != TLS_RECORD_TYPE_HANDSHAKE))
  

•           return 0;
  

•   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_sw_context_rx *rx_ctx = ctx->priv_ctx_rx;
  

•           WRITE_ONCE(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) {

@@ -1739,6 +1769,10 @@ 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(tls_ctx, darg->skb);
  

I think you can directly return from here.

Best regards, Parthiban V

•   if (err < 0)
  

•           return err;
  

•    return 0;
  

  }

@@ -2719,6 +2753,7 @@ int tls_set_sw_offload(struct sock *sk, int tx) crypto_info = &ctx->crypto_recv.info; cctx = &ctx->rx; aead = &sw_ctx_rx->aead_recv;

•           sw_ctx_rx->key_update_pending = false;
     }
  
     cipher_desc = get_cipher_desc(crypto_info->cipher_type);
  

-- 2.47.0