nvme-auth: add hkdf_expand_label()

Provide an implementation of RFC 8446 (TLS 1.3) HKDF-Expand-Label

Signed-off-by: Chris Leech <cleech@redhat.com>
Signed-off-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>

Author: cleech

drivers/nvme/common/auth.c

@@ -683,6 +683,59 @@ int nvme_auth_generate_digest(u8 hmac_id, u8 *psk, size_t psk_len,
 }
 EXPORT_SYMBOL_GPL(nvme_auth_generate_digest);
 
+/**
+ * hkdf_expand_label - HKDF-Expand-Label (RFC 8846 section 7.1)
+ * @hmac_tfm: hash context keyed with pseudorandom key
+ * @label: ASCII label without "tls13 " prefix
+ * @labellen: length of @label
+ * @context: context bytes
+ * @contextlen: length of @context
+ * @okm: output keying material
+ * @okmlen: length of @okm
+ *
+ * Build the TLS 1.3 HkdfLabel structure and invoke hkdf_expand().
+ *
+ * Returns 0 on success with output keying material stored in @okm,
+ * or a negative errno value otherwise.
+ */
+static int hkdf_expand_label(struct crypto_shash *hmac_tfm,
+		const u8 *label, unsigned int labellen,
+		const u8 *context, unsigned int contextlen,
+		u8 *okm, unsigned int okmlen)
+{
+	int err;
+	u8 *info;
+	unsigned int infolen;
+	const char *tls13_prefix = "tls13 ";
+	unsigned int prefixlen = strlen(tls13_prefix);
+
+	if (WARN_ON(labellen > (255 - prefixlen)))
+		return -EINVAL;
+	if (WARN_ON(contextlen > 255))
+		return -EINVAL;
+
+	infolen = 2 + (1 + prefixlen + labellen) + (1 + contextlen);
+	info = kzalloc(infolen, GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+
+	/* HkdfLabel.Length */
+	put_unaligned_be16(okmlen, info);
+
+	/* HkdfLabel.Label */
+	info[2] = prefixlen + labellen;
+	memcpy(info + 3, tls13_prefix, prefixlen);
+	memcpy(info + 3 + prefixlen, label, labellen);
+
+	/* HkdfLabel.Context */
+	info[3 + prefixlen + labellen] = contextlen;
+	memcpy(info + 4 + prefixlen + labellen, context, contextlen);
+
+	err = hkdf_expand(hmac_tfm, info, infolen, okm, okmlen);
+	kfree_sensitive(info);
+	return err;
+}
+
 /**
  * nvme_auth_derive_tls_psk - Derive TLS PSK
  * @hmac_id: Hash function identifier