[PATCH 02/10] nvme: add nvme_auth_generate_psk()

[Hannes Reinecke]

Add a function to generate a NVMe PSK from the shared credentials
negotiated by DH-HMAC-CHAP.

Signed-off-by: Hannes Reinecke <hare at kernel.org>
Reviewed-by: Sagi Grimberg <sagi at grimberg.me>
---
 drivers/nvme/common/auth.c | 87 ++++++++++++++++++++++++++++++++++++++
 include/linux/nvme-auth.h  |  3 ++
 2 files changed, 90 insertions(+)

diff --git a/drivers/nvme/common/auth.c b/drivers/nvme/common/auth.c
index 9b7126e1a19d..76e4a12f005e 100644
--- a/drivers/nvme/common/auth.c
+++ b/drivers/nvme/common/auth.c
@@ -11,6 +11,7 @@
 #include <linux/unaligned.h>
 #include <crypto/hash.h>
 #include <crypto/dh.h>
+#include <crypto/hkdf.h>
 #include <linux/nvme.h>
 #include <linux/nvme-auth.h>
 
@@ -471,5 +472,91 @@ int nvme_auth_generate_key(u8 *secret, struct nvme_dhchap_key **ret_key)
 }
 EXPORT_SYMBOL_GPL(nvme_auth_generate_key);
 
+/**
+ * nvme_auth_generate_psk - Generate a PSK for TLS
+ * @hmac_id: Hash function identifier
+ * @skey: Session key
+ * @skey_len: Length of @skey
+ * @c1: Value of challenge C1
+ * @c2: Value of challenge C2
+ * @hash_len: Hash length of the hash algorithm
+ * @ret_psk: Pointer too the resulting generated PSK
+ * @ret_len: length of @ret_psk
+ *
+ * Generate a PSK for TLS as specified in NVMe base specification, section
+ * 8.13.5.9: Generated PSK for TLS
+ *
+ * The generated PSK for TLS shall be computed applying the HMAC function
+ * using the hash function H( ) selected by the HashID parameter in the
+ * DH-HMAC-CHAP_Challenge message with the session key KS as key to the
+ * concatenation of the two challenges C1 and C2 (i.e., generated
+ * PSK = HMAC(KS, C1 || C2)).
+ *
+ * Returns 0 on success with a valid generated PSK pointer in @ret_psk and
+ * the length of @ret_psk in @ret_len, or a negative error number otherwise.
+ */
+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)
+{
+	struct crypto_shash *tfm;
+	SHASH_DESC_ON_STACK(shash, tfm);
+	u8 *psk;
+	const char *hmac_name;
+	int ret, psk_len;
+
+	if (!c1 || !c2)
+		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;
+	}
+
+	tfm = crypto_alloc_shash(hmac_name, 0, 0);
+	if (IS_ERR(tfm))
+		return PTR_ERR(tfm);
+
+	psk_len = crypto_shash_digestsize(tfm);
+	psk = kzalloc(psk_len, GFP_KERNEL);
+	if (!psk) {
+		ret = -ENOMEM;
+		goto out_free_tfm;
+	}
+
+	shash->tfm = tfm;
+	ret = crypto_shash_setkey(tfm, skey, skey_len);
+	if (ret)
+		goto out_free_psk;
+
+	ret = crypto_shash_init(shash);
+	if (ret)
+		goto out_free_psk;
+
+	ret = crypto_shash_update(shash, c1, hash_len);
+	if (ret)
+		goto out_free_psk;
+
+	ret = crypto_shash_update(shash, c2, hash_len);
+	if (ret)
+		goto out_free_psk;
+
+	ret = crypto_shash_final(shash, psk);
+	if (!ret) {
+		*ret_psk = psk;
+		*ret_len = psk_len;
+	}
+
+out_free_psk:
+	if (ret)
+		kfree_sensitive(psk);
+out_free_tfm:
+	crypto_free_shash(tfm);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(nvme_auth_generate_psk);
+
 MODULE_DESCRIPTION("NVMe Authentication framework");
 MODULE_LICENSE("GPL v2");
diff --git a/include/linux/nvme-auth.h b/include/linux/nvme-auth.h
index c1d0bc5d9624..b13884b04dfd 100644
--- a/include/linux/nvme-auth.h
+++ b/include/linux/nvme-auth.h
@@ -40,5 +40,8 @@ int nvme_auth_gen_pubkey(struct crypto_kpp *dh_tfm,
 int nvme_auth_gen_shared_secret(struct crypto_kpp *dh_tfm,
 				u8 *ctrl_key, size_t ctrl_key_len,
 				u8 *sess_key, size_t sess_key_len);
+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);
 
 #endif /* _NVME_AUTH_H */
-- 
2.35.3