net/tls: Implement getsockopt SOL_TLS TLS_RX

Implement the getsockopt SOL_TLS TLS_RX which is currently missing. The
primary usecase is to use it in conjunction with TCP_REPAIR to
checkpoint/restore the TLS record layer state.

TLS connection state usually exists on the user space library. So
basically we can easily extract it from there, but when the TLS
connections are delegated to the kTLS, it is not the case. We need to
have a way to extract the TLS state from the kernel for both of TX and
RX side.

The new TLS_RX getsockopt copies the crypto_info to user in the same
way as TLS_TX does.

We have described use cases in our research work in Netdev 0x14
Transport Workshop [1].

Also, there is an TLS implementation called tlse [2] which supports
TLS connection migration. They have support of kTLS and their code
shows that they are expecting the future support of this option.

[1] https://speakerdeck.com/yutarohayakawa/prism-proxies-without-the-pain
[2] https://github.com/eduardsui/tlseSigned-off-by: Yutaro Hayakawa <yhayakawa3720@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tls/tls_main.c

@@ -330,12 +330,13 @@ static void tls_sk_proto_close(struct sock *sk, long timeout)
 		tls_ctx_free(sk, ctx);
 }
 
-static int do_tls_getsockopt_tx(struct sock *sk, char __user *optval,
-				int __user *optlen)
+static int do_tls_getsockopt_conf(struct sock *sk, char __user *optval,
+				  int __user *optlen, int tx)
 {
 	int rc = 0;
 	struct tls_context *ctx = tls_get_ctx(sk);
 	struct tls_crypto_info *crypto_info;
+	struct cipher_context *cctx;
 	int len;
 
 	if (get_user(len, optlen))
@@ -352,7 +353,13 @@ static int do_tls_getsockopt_tx(struct sock *sk, char __user *optval,
 	}
 
 	/* get user crypto info */
-	crypto_info = &ctx->crypto_send.info;
+	if (tx) {
+		crypto_info = &ctx->crypto_send.info;
+		cctx = &ctx->tx;
+	} else {
+		crypto_info = &ctx->crypto_recv.info;
+		cctx = &ctx->rx;
+	}
 
 	if (!TLS_CRYPTO_INFO_READY(crypto_info)) {
 		rc = -EBUSY;
@@ -379,9 +386,9 @@ static int do_tls_getsockopt_tx(struct sock *sk, char __user *optval,
 		}
 		lock_sock(sk);
 		memcpy(crypto_info_aes_gcm_128->iv,
-		       ctx->tx.iv + TLS_CIPHER_AES_GCM_128_SALT_SIZE,
+		       cctx->iv + TLS_CIPHER_AES_GCM_128_SALT_SIZE,
 		       TLS_CIPHER_AES_GCM_128_IV_SIZE);
-		memcpy(crypto_info_aes_gcm_128->rec_seq, ctx->tx.rec_seq,
+		memcpy(crypto_info_aes_gcm_128->rec_seq, cctx->rec_seq,
 		       TLS_CIPHER_AES_GCM_128_REC_SEQ_SIZE);
 		release_sock(sk);
 		if (copy_to_user(optval,
@@ -403,9 +410,9 @@ static int do_tls_getsockopt_tx(struct sock *sk, char __user *optval,
 		}
 		lock_sock(sk);
 		memcpy(crypto_info_aes_gcm_256->iv,
-		       ctx->tx.iv + TLS_CIPHER_AES_GCM_256_SALT_SIZE,
+		       cctx->iv + TLS_CIPHER_AES_GCM_256_SALT_SIZE,
 		       TLS_CIPHER_AES_GCM_256_IV_SIZE);
-		memcpy(crypto_info_aes_gcm_256->rec_seq, ctx->tx.rec_seq,
+		memcpy(crypto_info_aes_gcm_256->rec_seq, cctx->rec_seq,
 		       TLS_CIPHER_AES_GCM_256_REC_SEQ_SIZE);
 		release_sock(sk);
 		if (copy_to_user(optval,
@@ -429,7 +436,9 @@ static int do_tls_getsockopt(struct sock *sk, int optname,
 
 	switch (optname) {
 	case TLS_TX:
-		rc = do_tls_getsockopt_tx(sk, optval, optlen);
+	case TLS_RX:
+		rc = do_tls_getsockopt_conf(sk, optval, optlen,
+					    optname == TLS_TX);
 		break;
 	default:
 		rc = -ENOPROTOOPT;