nvmet-auth: Diffie-Hellman key exchange support

Implement Diffie-Hellman key exchange using FFDHE groups for NVMe
In-Band Authentication.
This patch adds a new host configfs attribute 'dhchap_dhgroup' to
select the FFDHE group to use.

Signed-off-by: Hannes Reinecke <hare@suse.de>

drivers/nvme/target/Kconfig

@@ -90,6 +90,7 @@ config NVME_TARGET_AUTH
 	select CRYPTO_HMAC
 	select CRYPTO_SHA256
 	select CRYPTO_SHA512
+	select CRYPTO_FFDHE
 	help
 	  This enables support for NVMe over Fabrics In-band Authentication
 

drivers/nvme/target/auth.c

@@ -53,6 +53,71 @@ int nvmet_auth_set_host_key(struct nvmet_host *host, const char *secret)
 	return 0;
 }
 
+int nvmet_setup_dhgroup(struct nvmet_ctrl *ctrl, int dhgroup_id)
+{
+	struct nvmet_host_link *p;
+	struct nvmet_host *host = NULL;
+	const char *dhgroup_kpp;
+	int ret = -ENOTSUPP;
+
+	if (dhgroup_id == NVME_AUTH_DHCHAP_DHGROUP_NULL)
+		return 0;
+
+	down_read(&nvmet_config_sem);
+	if (ctrl->subsys->type == NVME_NQN_DISC)
+		goto out_unlock;
+
+	list_for_each_entry(p, &ctrl->subsys->hosts, entry) {
+		if (strcmp(nvmet_host_name(p->host), ctrl->hostnqn))
+			continue;
+		host = p->host;
+		break;
+	}
+	if (!host) {
+		pr_debug("host %s not found\n", ctrl->hostnqn);
+		ret = -ENXIO;
+		goto out_unlock;
+	}
+
+	if (host->dhchap_dhgroup_id != dhgroup_id) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+	if (ctrl->dh_tfm) {
+		if (ctrl->dh_gid == dhgroup_id) {
+			pr_debug("reuse existing DH group %d\n", dhgroup_id);
+			ret = 0;
+		} else {
+			pr_debug("DH group mismatch (selected %d, requested %d)\n",
+				 ctrl->dh_gid, dhgroup_id);
+			ret = -EINVAL;
+		}
+		goto out_unlock;
+	}
+
+	dhgroup_kpp = nvme_auth_dhgroup_kpp(dhgroup_id);
+	if (!dhgroup_kpp) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+	ctrl->dh_tfm = crypto_alloc_kpp(dhgroup_kpp, 0, 0);
+	if (IS_ERR(ctrl->dh_tfm)) {
+		pr_debug("failed to setup DH group %d, err %ld\n",
+			 dhgroup_id, PTR_ERR(ctrl->dh_tfm));
+		ret = PTR_ERR(ctrl->dh_tfm);
+		ctrl->dh_tfm = NULL;
+	} else {
+		ctrl->dh_gid = dhgroup_id;
+		ctrl->dh_keysize = nvme_auth_dhgroup_pubkey_size(dhgroup_id);
+		ret = 0;
+	}
+
+out_unlock:
+	up_read(&nvmet_config_sem);
+
+	return ret;
+}
+
 int nvmet_setup_auth(struct nvmet_ctrl *ctrl)
 {
 	int ret = 0;
@@ -147,6 +212,11 @@ void nvmet_destroy_auth(struct nvmet_ctrl *ctrl)
 		ctrl->shash_tfm = NULL;
 		ctrl->shash_id = 0;
 	}
+	if (ctrl->dh_tfm) {
+		crypto_free_kpp(ctrl->dh_tfm);
+		ctrl->dh_tfm = NULL;
+		ctrl->dh_gid = 0;
+	}
 	if (ctrl->dhchap_key) {
 		kfree(ctrl->dhchap_key);
 		ctrl->dhchap_key = NULL;
@@ -182,8 +252,18 @@ int nvmet_auth_host_hash(struct nvmet_req *req, u8 *response,
 		return ret;
 	}
 	if (ctrl->dh_gid != NVME_AUTH_DHCHAP_DHGROUP_NULL) {
-		ret = -ENOTSUPP;
-		goto out;
+		challenge = kmalloc(shash_len, GFP_KERNEL);
+		if (!challenge) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		ret = nvme_auth_augmented_challenge(ctrl->shash_id,
+						    req->sq->dhchap_skey,
+						    req->sq->dhchap_skey_len,
+						    req->sq->dhchap_c1,
+						    challenge, shash_len);
+		if (ret)
+			goto out;
 	}
 
 	shash->tfm = ctrl->shash_tfm;
@@ -256,8 +336,18 @@ int nvmet_auth_ctrl_hash(struct nvmet_req *req, u8 *response,
 		return ret;
 	}
 	if (ctrl->dh_gid != NVME_AUTH_DHCHAP_DHGROUP_NULL) {
-		ret = -ENOTSUPP;
-		goto out;
+		challenge = kmalloc(shash_len, GFP_KERNEL);
+		if (!challenge) {
+			ret = -ENOMEM;
+			goto out;
+		}
+		ret = nvme_auth_augmented_challenge(ctrl->shash_id,
+						    req->sq->dhchap_skey,
+						    req->sq->dhchap_skey_len,
+						    req->sq->dhchap_c2,
+						    challenge, shash_len);
+		if (ret)
+			goto out;
 	}
 
 	shash->tfm = ctrl->shash_tfm;
@@ -299,3 +389,53 @@ int nvmet_auth_ctrl_hash(struct nvmet_req *req, u8 *response,
 	kfree_sensitive(ctrl_response);
 	return 0;
 }
+
+int nvmet_auth_ctrl_exponential(struct nvmet_req *req,
+				u8 *buf, int buf_size)
+{
+	struct nvmet_ctrl *ctrl = req->sq->ctrl;
+	int ret;
+
+	if (!ctrl->dh_tfm) {
+		pr_warn("No DH algorithm!\n");
+		return -ENOKEY;
+	}
+	ret = nvme_auth_gen_pubkey(ctrl->dh_tfm, buf, buf_size);
+	if (ret == -EOVERFLOW) {
+		pr_debug("public key buffer too small, need %d is %d\n",
+			 crypto_kpp_maxsize(ctrl->dh_tfm), buf_size);
+		ret = -ENOKEY;
+	} else if (ret) {
+		pr_debug("failed to generate public key, err %d\n", ret);
+		ret = -ENOKEY;
+	} else
+		pr_debug("%s: ctrl public key %*ph\n", __func__,
+			 (int)buf_size, buf);
+
+	return ret;
+}
+
+int nvmet_auth_ctrl_sesskey(struct nvmet_req *req,
+			    u8 *pkey, int pkey_size)
+{
+	struct nvmet_ctrl *ctrl = req->sq->ctrl;
+	int ret;
+
+	req->sq->dhchap_skey_len =
+		nvme_auth_dhgroup_privkey_size(ctrl->dh_gid);
+	req->sq->dhchap_skey = kzalloc(req->sq->dhchap_skey_len, GFP_KERNEL);
+	if (!req->sq->dhchap_skey)
+		return -ENOMEM;
+	ret = nvme_auth_gen_shared_secret(ctrl->dh_tfm,
+					  pkey, pkey_size,
+					  req->sq->dhchap_skey,
+					  req->sq->dhchap_skey_len);
+	if (ret)
+		pr_debug("failed to compute shared secred, err %d\n", ret);
+	else
+		pr_debug("%s: shared secret %*ph\n", __func__,
+			 (int)req->sq->dhchap_skey_len,
+			 req->sq->dhchap_skey);
+
+	return ret;
+}

drivers/nvme/target/configfs.c

@@ -1712,9 +1712,40 @@ static ssize_t nvmet_host_dhchap_hash_store(struct config_item *item,
 
 CONFIGFS_ATTR(nvmet_host_, dhchap_hash);
 
+static ssize_t nvmet_host_dhchap_dhgroup_show(struct config_item *item,
+		char *page)
+{
+	struct nvmet_host *host = to_host(item);
+	const char *dhgroup = nvme_auth_dhgroup_name(host->dhchap_dhgroup_id);
+
+	return sprintf(page, "%s\n", dhgroup ? dhgroup : "none");
+}
+
+static ssize_t nvmet_host_dhchap_dhgroup_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct nvmet_host *host = to_host(item);
+	int dhgroup_id;
+
+	dhgroup_id = nvme_auth_dhgroup_id(page);
+	if (dhgroup_id < 0)
+		return -EINVAL;
+	if (dhgroup_id != NVME_AUTH_DHCHAP_DHGROUP_NULL) {
+		const char *kpp = nvme_auth_dhgroup_kpp(dhgroup_id);
+
+		if (!crypto_has_kpp(kpp, 0, 0))
+			return -EINVAL;
+	}
+	host->dhchap_dhgroup_id = dhgroup_id;
+	return count;
+}
+
+CONFIGFS_ATTR(nvmet_host_, dhchap_dhgroup);
+
 static struct configfs_attribute *nvmet_host_attrs[] = {
 	&nvmet_host_attr_dhchap_key,
 	&nvmet_host_attr_dhchap_hash,
+	&nvmet_host_attr_dhchap_dhgroup,
 	NULL,
 };
 #endif /* CONFIG_NVME_TARGET_AUTH */

drivers/nvme/target/fabrics-cmd-auth.c

@@ -64,13 +64,24 @@ static u16 nvmet_auth_negotiate(struct nvmet_req *req, void *d)
 			null_dh = dhgid;
 			continue;
 		}
+		if (ctrl->dh_tfm && ctrl->dh_gid == dhgid) {
+			pr_debug("%s: ctrl %d qid %d: reusing existing DH group %d\n",
+				 __func__, ctrl->cntlid, req->sq->qid, dhgid);
+			break;
+		}
+		if (nvmet_setup_dhgroup(ctrl, dhgid) < 0)
+			continue;
+		if (nvme_auth_gen_privkey(ctrl->dh_tfm, dhgid) == 0)
+			break;
+		crypto_free_kpp(ctrl->dh_tfm);
+		ctrl->dh_tfm = NULL;
+		ctrl->dh_gid = 0;
 	}
-	if (null_dh < 0) {
+	if (!ctrl->dh_tfm && null_dh < 0) {
 		pr_debug("%s: ctrl %d qid %d: no DH group selected\n",
 			 __func__, ctrl->cntlid, req->sq->qid);
 		return NVME_AUTH_DHCHAP_FAILURE_DHGROUP_UNUSABLE;
 	}
-	ctrl->dh_gid = null_dh;
 	pr_debug("%s: ctrl %d qid %d: DH group %s (%d)\n",
 		 __func__, ctrl->cntlid, req->sq->qid,
 		 nvme_auth_dhgroup_name(ctrl->dh_gid), ctrl->dh_gid);
@@ -91,7 +102,11 @@ static u16 nvmet_auth_reply(struct nvmet_req *req, void *d)
 		return NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
 
 	if (data->dhvlen) {
-		return NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
+		if (!ctrl->dh_tfm)
+			return NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
+		if (nvmet_auth_ctrl_sesskey(req, data->rval + 2 * data->hl,
+					    data->dhvlen) < 0)
+			return NVME_AUTH_DHCHAP_FAILURE_DHGROUP_UNUSABLE;
 	}
 
 	response = kmalloc(data->hl, GFP_KERNEL);
@@ -232,6 +247,7 @@ void nvmet_execute_auth_send(struct nvmet_req *req)
 			NVME_AUTH_DHCHAP_FAILURE_INCORRECT_PAYLOAD;
 		goto done_kfree;
 	}
+
 	switch (data->auth_id) {
 	case NVME_AUTH_DHCHAP_MESSAGE_REPLY:
 		status = nvmet_auth_reply(req, d);
@@ -303,6 +319,8 @@ static int nvmet_auth_challenge(struct nvmet_req *req, void *d, int al)
 	int hash_len = crypto_shash_digestsize(ctrl->shash_tfm);
 	int data_size = sizeof(*d) + hash_len;
 
+	if (ctrl->dh_tfm)
+		data_size += ctrl->dh_keysize;
 	if (al < data_size) {
 		pr_debug("%s: buffer too small (al %d need %d)\n", __func__,
 			 al, data_size);
@@ -321,6 +339,12 @@ static int nvmet_auth_challenge(struct nvmet_req *req, void *d, int al)
 		return -ENOMEM;
 	get_random_bytes(req->sq->dhchap_c1, data->hl);
 	memcpy(data->cval, req->sq->dhchap_c1, data->hl);
+	if (ctrl->dh_tfm) {
+		data->dhgid = ctrl->dh_gid;
+		data->dhvlen = ctrl->dh_keysize;
+		ret = nvmet_auth_ctrl_exponential(req, data->cval + data->hl,
+						  data->dhvlen);
+	}
 	pr_debug("%s: ctrl %d qid %d seq %d transaction %d hl %d dhvlen %d\n",
 		 __func__, ctrl->cntlid, req->sq->qid, req->sq->dhchap_s1,
 		 req->sq->dhchap_tid, data->hl, data->dhvlen);

drivers/nvme/target/nvmet.h

@@ -227,6 +227,7 @@ struct nvmet_ctrl {
 	size_t			dhchap_key_len;
 	struct crypto_shash	*shash_tfm;
 	u8			shash_id;
+	struct crypto_kpp	*dh_tfm;
 	u32			dh_gid;
 	u32			dh_keysize;
 #endif
@@ -693,6 +694,7 @@ int nvmet_setup_auth(struct nvmet_ctrl *ctrl);
 void nvmet_init_auth(struct nvmet_ctrl *ctrl, struct nvmet_req *req);
 void nvmet_destroy_auth(struct nvmet_ctrl *ctrl);
 void nvmet_auth_sq_free(struct nvmet_sq *sq);
+int nvmet_setup_dhgroup(struct nvmet_ctrl *ctrl, int dhgroup_id);
 bool nvmet_check_auth_status(struct nvmet_req *req);
 int nvmet_auth_host_hash(struct nvmet_req *req, u8 *response,
 			 unsigned int hash_len);
@@ -702,6 +704,10 @@ static inline bool nvmet_has_auth(struct nvmet_ctrl *ctrl)
 {
 	return ctrl->shash_tfm != NULL;
 }
+int nvmet_auth_ctrl_exponential(struct nvmet_req *req,
+				u8 *buf, int buf_size);
+int nvmet_auth_ctrl_sesskey(struct nvmet_req *req,
+			    u8 *buf, int buf_size);
 #else
 static inline int nvmet_setup_auth(struct nvmet_ctrl *ctrl)
 {