nvme: add nvme_auth_generate_digest()

Add a function to calculate the PSK digest as specified in TP8018.

Signed-off-by: Hannes Reinecke <hare@kernel.org>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/common/auth.c

@@ -558,5 +558,139 @@ int nvme_auth_generate_psk(u8 hmac_id, u8 *skey, size_t skey_len,
 }
 EXPORT_SYMBOL_GPL(nvme_auth_generate_psk);
 
+/**
+ * nvme_auth_generate_digest - Generate TLS PSK digest
+ * @hmac_id: Hash function identifier
+ * @psk: Generated input PSK
+ * @psk_len: Length of @psk
+ * @subsysnqn: NQN of the subsystem
+ * @hostnqn: NQN of the host
+ * @ret_digest: Pointer to the returned digest
+ *
+ * Generate a TLS PSK digest as specified in TP8018 Section 3.6.1.3:
+ *   TLS PSK and PSK identity Derivation
+ *
+ * The PSK digest shall be computed by encoding in Base64 (refer to RFC
+ * 4648) the result of the application of the HMAC function using the hash
+ * function specified in item 4 above (ie the hash function of the cipher
+ * suite associated with the PSK identity) with the PSK as HMAC key to the
+ * concatenation of:
+ * - the NQN of the host (i.e., NQNh) not including the null terminator;
+ * - a space character;
+ * - the NQN of the NVM subsystem (i.e., NQNc) not including the null
+ *   terminator;
+ * - a space character; and
+ * - the seventeen ASCII characters "NVMe-over-Fabrics"
+ * (i.e., <PSK digest> = Base64(HMAC(PSK, NQNh || " " || NQNc || " " ||
+ *  "NVMe-over-Fabrics"))).
+ * The length of the PSK digest depends on the hash function used to compute
+ * it as follows:
+ * - If the SHA-256 hash function is used, the resulting PSK digest is 44
+ *   characters long; or
+ * - If the SHA-384 hash function is used, the resulting PSK digest is 64
+ *   characters long.
+ *
+ * Returns 0 on success with a valid digest pointer in @ret_digest, or a
+ * negative error number on failure.
+ */
+int nvme_auth_generate_digest(u8 hmac_id, u8 *psk, size_t psk_len,
+		char *subsysnqn, char *hostnqn, u8 **ret_digest)
+{
+	struct crypto_shash *tfm;
+	SHASH_DESC_ON_STACK(shash, tfm);
+	u8 *digest, *enc;
+	const char *hmac_name;
+	size_t digest_len, hmac_len;
+	int ret;
+
+	if (WARN_ON(!subsysnqn || !hostnqn))
+		return -EINVAL;
+
+	hmac_name = nvme_auth_hmac_name(hmac_id);
+	if (!hmac_name) {
+		pr_warn("%s: invalid hash algorithm %d\n",
+			__func__, hmac_id);
+		return -EINVAL;
+	}
+
+	switch (nvme_auth_hmac_hash_len(hmac_id)) {
+	case 32:
+		hmac_len = 44;
+		break;
+	case 48:
+		hmac_len = 64;
+		break;
+	default:
+		pr_warn("%s: invalid hash algorithm '%s'\n",
+			__func__, hmac_name);
+		return -EINVAL;
+	}
+
+	enc = kzalloc(hmac_len + 1, GFP_KERNEL);
+	if (!enc)
+		return -ENOMEM;
+
+	tfm = crypto_alloc_shash(hmac_name, 0, 0);
+	if (IS_ERR(tfm)) {
+		ret = PTR_ERR(tfm);
+		goto out_free_enc;
+	}
+
+	digest_len = crypto_shash_digestsize(tfm);
+	digest = kzalloc(digest_len, GFP_KERNEL);
+	if (!digest) {
+		ret = -ENOMEM;
+		goto out_free_tfm;
+	}
+
+	shash->tfm = tfm;
+	ret = crypto_shash_setkey(tfm, psk, psk_len);
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_init(shash);
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_update(shash, hostnqn, strlen(hostnqn));
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_update(shash, " ", 1);
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_update(shash, subsysnqn, strlen(subsysnqn));
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_update(shash, " NVMe-over-Fabrics", 18);
+	if (ret)
+		goto out_free_digest;
+
+	ret = crypto_shash_final(shash, digest);
+	if (ret)
+		goto out_free_digest;
+
+	ret = base64_encode(digest, digest_len, enc);
+	if (ret < hmac_len) {
+		ret = -ENOKEY;
+		goto out_free_digest;
+	}
+	*ret_digest = enc;
+	ret = 0;
+
+out_free_digest:
+	kfree_sensitive(digest);
+out_free_tfm:
+	crypto_free_shash(tfm);
+out_free_enc:
+	if (ret)
+		kfree_sensitive(enc);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nvme_auth_generate_digest);
+
 MODULE_DESCRIPTION("NVMe Authentication framework");
 MODULE_LICENSE("GPL v2");

include/linux/nvme-auth.h

@@ -43,5 +43,7 @@ int nvme_auth_gen_shared_secret(struct crypto_kpp *dh_tfm,
 int nvme_auth_generate_psk(u8 hmac_id, u8 *skey, size_t skey_len,
 			   u8 *c1, u8 *c2, size_t hash_len,
 			   u8 **ret_psk, size_t *ret_len);
+int nvme_auth_generate_digest(u8 hmac_id, u8 *psk, size_t psk_len,
+		char *subsysnqn, char *hostnqn, u8 **ret_digest);
 
 #endif /* _NVME_AUTH_H */