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>

diff --git a/drivers/nvme/common/auth.c b/drivers/nvme/common/auth.c
index 91e273b89fea3860f521aaa4127eb23f7f09bc60..c6eae8e6b6f993b840152c8415e43578e8ec85d8 100644 (file)
--- a/drivers/nvme/common/auth.c
+++ b/drivers/nvme/common/auth.c
@@ -683,6 +683,59 @@ out_free_enc:
 }
 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