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

[Sabrina Dubroca <sd@queasysnail.net>]

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@queasysnail.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;
 
 	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);
+
+	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