Re: [PATCH RFC net-next v2 3/5] tls: update the RX key when a KeyUpdate is received

From: Martin Belanger <redacted>

When a KeyUpdate arrives, kTLS blocks reads with -EKEYEXPIRED until
the user installs the next key. A kernel user such as nvme-tcp or
sunrpc never does, so the connection stalls.

For a socket with a registered RX secret, derive the next key and
install it when the KeyUpdate is decrypted. The record is not passed to
the user, so recvmsg(), splice() and read_sock() go on to the next
record. Without a registered secret the behavior is unchanged.

A KeyUpdate that is not alone in its record, has a wrong length or an
invalid request_update value ends the connection, as RFC 9846 section
4.7.3 requires. So does a peer that sends more than 8 KeyUpdates in one
second, the same limit as GnuTLS.

Assisted-by: LLM
Signed-off-by: Martin Belanger <redacted>
---
  include/net/tls.h       |   7 +++
  net/tls/Makefile        |   3 +-
  net/tls/tls.h           |   2 +
  net/tls/tls_keyupdate.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++++
  net/tls/tls_sw.c        |  43 ++++++++++++--
  5 files changed, 198 insertions(+), 7 deletions(-)

diff --git a/include/net/tls.h b/include/net/tls.h
index aacc6d12226e..a5bc28a7d1f5 100644
--- a/include/net/tls.h
+++ b/include/net/tls.h

@@ -63,6 +63,11 @@ struct tls_rec;
  
  #define TLS_HANDSHAKE_KEYUPDATE		24	/* rfc8446 B.3: Key update */
  
+/* KeyUpdate: msg_type, 24-bit length, request_update (RFC 9846 4.7.3) */
+#define TLS_KEYUPDATE_MSG_SIZE		5
+#define TLS_KEY_UPDATE_NOT_REQUESTED	0
+#define TLS_KEY_UPDATE_REQUESTED	1
+
  #define TLS_AAD_SPACE_SIZE		13
  
  /* SHA-384, the longest hash of a TLS 1.3 cipher suite kTLS supports */

@@ -142,6 +147,8 @@ struct tls_sw_context_rx {
  	u8 zc_capable:1;
  	u8 reader_contended:1;
  	bool key_update_pending;
+	u8 key_update_count;		/* received in this window */
+	unsigned long key_update_window;	/* jiffies */
  
  	struct tls_strparser strp;
  

diff --git a/net/tls/Makefile b/net/tls/Makefile
index 6edcf1271b75..ce8ac6a59f8c 100644
--- a/net/tls/Makefile
+++ b/net/tls/Makefile

@@ -7,6 +7,7 @@ CFLAGS_trace.o := -I$(src)
  
  obj-$(CONFIG_TLS) += tls.o
  
-tls-y := tls_main.o tls_sw.o tls_proc.o trace.o tls_strp.o tls_hkdf.o
+tls-y := tls_main.o tls_sw.o tls_proc.o trace.o tls_strp.o tls_hkdf.o \
+	 tls_keyupdate.o
  
  tls-$(CONFIG_TLS_DEVICE) += tls_device.o tls_device_fallback.o

diff --git a/net/tls/tls.h b/net/tls/tls.h
index b2061f6bf065..63ece8074985 100644
--- a/net/tls/tls.h
+++ b/net/tls/tls.h

@@ -149,6 +149,8 @@ int init_prot_info(struct tls_prot_info *prot,
  		   const struct tls_cipher_desc *cipher_desc);
  int tls_hkdf_expand_label(const u8 *secret, size_t secret_len,
  			  const char *label, u8 *out, size_t out_len);
+int tls_keyupdate_rekey(struct sock *sk, int tx);
+int tls_keyupdate_rx(struct sock *sk, struct sk_buff *skb);
  int tls_set_sw_offload(struct sock *sk, int tx,
  		       struct tls_crypto_info *new_crypto_info);
  void tls_update_rx_zc_capable(struct tls_context *tls_ctx);

diff --git a/net/tls/tls_keyupdate.c b/net/tls/tls_keyupdate.c
new file mode 100644
index 000000000000..543bf57599c7
--- /dev/null
+++ b/net/tls/tls_keyupdate.c

@@ -0,0 +1,150 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2026 Dell Technologies Inc. or its subsidiaries.
+ *
+ * TLS 1.3 KeyUpdate, RFC 9846 sections 4.7.3 and 7.2.
+ *
+ * A TLS 1.3 peer can change the key of the direction it sends in at any
+ * time. It sends a KeyUpdate message, then encrypts all later records
+ * with the next key. A sender must also change its key before the key
+ * has protected too many records (section 5.5).
+ *
+ * The next key is derived from the application traffic secret, not from
+ * the current key. User space gives the kernel only the key and IV, so
+ * the kernel cannot derive the next key on its own. Without the secret,
+ * a received KeyUpdate goes to the application, and the kernel stops
+ * decrypting until the application installs the next key with TLS_RX.
+ *
+ * With TLS_TX_TRAFFIC_SECRET or TLS_RX_TRAFFIC_SECRET, user space also
+ * gives the kernel the secret of that direction. The kernel then handles
+ * KeyUpdate itself. This file derives and installs the next key, and
+ * processes a received KeyUpdate. tls_sw.c sends KeyUpdate messages.
+ */
+
+#include <linux/jiffies.h>
+#include <linux/skbuff.h>
+#include <net/strparser.h>
+#include <net/tls.h>
+
+#include "tls.h"
+
+/* A peer that sends more KeyUpdates than this in one second ends the
+ * connection. Each one costs three HMACs and a new key, and carries no
+ * data.
+ */
+#define TLS_KEYUPDATE_RX_MAX_PER_SEC	8
+
+/**
+ * tls_keyupdate_rekey - install the next key of one direction
+ * @sk: socket
+ * @tx: non-zero for the transmit direction
+ *
+ * Derive the next application traffic secret from the registered one,
+ * then its key and IV, and install them. The record sequence number
+ * restarts at zero.
+ *
+ * Return: 0 on success, or a negative errno. On error the installed key
+ * and the registered secret do not change.
+ */
+int tls_keyupdate_rekey(struct sock *sk, int tx)
+{
+	struct tls_context *ctx = tls_get_ctx(sk);
+	struct tls_traffic_secret *secret;
+	const struct tls_cipher_desc *cipher_desc;
+	u8 iv[TLS_MAX_SALT_SIZE + TLS_MAX_IV_SIZE];
+	u8 next[TLS_MAX_TRAFFIC_SECRET_SIZE];
+	union tls_crypto_context tmp = {};
+	struct tls_crypto_info *info = &tmp.info;
+	int rc;
+
+	secret = tx ? &ctx->tx_secret : &ctx->rx_secret;
+	cipher_desc = get_cipher_desc(ctx->prot_info.cipher_type);
+	if (!cipher_desc || !secret->len ||
+	    cipher_desc->salt + cipher_desc->iv > sizeof(iv))
+		return -EINVAL;
+
+	/* version and cipher_type; the rest of tmp stays zero */
+	*info = tx ? ctx->crypto_send.info : ctx->crypto_recv.info;
+
+	rc = tls_hkdf_expand_label(secret->data, secret->len, "traffic upd",
+				   next, secret->len);
+	if (rc)
+		goto out;
+
+	rc = tls_hkdf_expand_label(next, secret->len, "key",
+				   crypto_info_key(info, cipher_desc),
+				   cipher_desc->key);
+	if (rc)
+		goto out;
+
+	rc = tls_hkdf_expand_label(next, secret->len, "iv", iv,
+				   cipher_desc->salt + cipher_desc->iv);
+	if (rc)
+		goto out;
+
+	memcpy(crypto_info_salt(info, cipher_desc), iv, cipher_desc->salt);
+	memcpy(crypto_info_iv(info, cipher_desc), iv + cipher_desc->salt,
+	       cipher_desc->iv);
+
+	rc = tls_set_sw_offload(sk, tx, info);
+	if (rc)
+		goto out;
+
+	memcpy(secret->data, next, secret->len);
+
+out:
+	memzero_explicit(next, sizeof(next));
+	memzero_explicit(iv, sizeof(iv));
+	memzero_explicit(&tmp, sizeof(tmp));
+
+	return rc;
+}
+
+/**
+ * tls_keyupdate_rx - process a received KeyUpdate
+ * @sk: socket
+ * @skb: the decrypted record, which starts with a KeyUpdate message
+ *
+ * Called with the socket locked, for a direction with a registered
+ * secret. The caller does not pass the record to the user.
+ *
+ * Return: 0 on success, or a negative errno if the connection must end.
+ */
+int tls_keyupdate_rx(struct sock *sk, struct sk_buff *skb)
+{
+	struct tls_context *ctx = tls_get_ctx(sk);
+	struct tls_sw_context_rx *rx_ctx = tls_sw_ctx_rx(ctx);
+	const struct strp_msg *rxm = strp_msg(skb);
+	u8 msg[TLS_KEYUPDATE_MSG_SIZE];
+	int rc;
+
+	/* A KeyUpdate must end its record (section 5.1). Another message
+	 * in the same record is not supported.
+	 */
+	if (rxm->full_len != sizeof(msg) ||
+	    skb_copy_bits(skb, rxm->offset, msg, sizeof(msg)))
+		return -EBADMSG;
+
+	/* msg_type, a 24-bit length of 1, then request_update */
+	if (msg[1] || msg[2] || msg[3] != 1)
+		return -EBADMSG;
+	if (msg[4] != TLS_KEY_UPDATE_NOT_REQUESTED &&
+	    msg[4] != TLS_KEY_UPDATE_REQUESTED)
+		return -EBADMSG;
+
+	if (!rx_ctx->key_update_count ||
+	    time_after(jiffies, rx_ctx->key_update_window + HZ)) {
+		rx_ctx->key_update_window = jiffies;
+		rx_ctx->key_update_count = 0;
+	}
+	if (++rx_ctx->key_update_count > TLS_KEYUPDATE_RX_MAX_PER_SEC)