Bluetooth: let the crypto subsystem generate the ecc privkey

That Bluetooth SMP knows about the private key is pointless, since the
detection of debug key usage is actually via the public key portion.
With this patch, the Bluetooth SMP will stop keeping a copy of the
ecdh private key and will let the crypto subsystem to generate and
handle the ecdh private key, potentially benefiting of hardware
ecc private key generation and retention.

The loop that tries to generate a correct private key is now removed and
we trust the crypto subsystem to generate a correct private key. This
backup logic should be done in crypto, if really needed.

Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

1 files changed, 29 insertions, 37 deletions

diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
index af7e6100e55b..d41449b9e9d6 100644
--- a/net/bluetooth/smp.c
+++ b/net/bluetooth/smp.c
@@ -84,7 +84,6 @@ enum {
 struct smp_dev {
 	/* Secure Connections OOB data */
 	u8			local_pk[64];
-	u8			local_sk[32];
 	u8			local_rand[16];
 	bool			debug_key;
 
@@ -126,7 +125,6 @@ struct smp_chan {
 
 	/* Secure Connections variables */
 	u8			local_pk[64];
-	u8			local_sk[32];
 	u8			remote_pk[64];
 	u8			dhkey[32];
 	u8			mackey[16];
@@ -568,24 +566,22 @@ int smp_generate_oob(struct hci_dev *hdev, u8 hash[16], u8 rand[16])
 
 	if (hci_dev_test_flag(hdev, HCI_USE_DEBUG_KEYS)) {
 		BT_DBG("Using debug keys");
+		err = set_ecdh_privkey(smp->tfm_ecdh, debug_sk);
+		if (err)
+			return err;
 		memcpy(smp->local_pk, debug_pk, 64);
-		memcpy(smp->local_sk, debug_sk, 32);
 		smp->debug_key = true;
 	} else {
 		while (true) {
-			/* Seed private key with random number */
-			get_random_bytes(smp->local_sk, 32);
-
-			/* Generate local key pair for Secure Connections */
-			err = generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk,
-						 smp->local_sk);
+			/* Generate key pair for Secure Connections */
+			err = generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk);
 			if (err)
 				return err;
 
 			/* This is unlikely, but we need to check that
 			 * we didn't accidentially generate a debug key.
 			 */
-			if (crypto_memneq(smp->local_sk, debug_sk, 32))
+			if (crypto_memneq(smp->local_pk, debug_pk, 64))
 				break;
 		}
 		smp->debug_key = false;
@@ -593,7 +589,6 @@ int smp_generate_oob(struct hci_dev *hdev, u8 hash[16], u8 rand[16])
 
 	SMP_DBG("OOB Public Key X: %32phN", smp->local_pk);
 	SMP_DBG("OOB Public Key Y: %32phN", smp->local_pk + 32);
-	SMP_DBG("OOB Private Key:  %32phN", smp->local_sk);
 
 	get_random_bytes(smp->local_rand, 16);
 
@@ -1900,7 +1895,6 @@ static u8 sc_send_public_key(struct smp_chan *smp)
 		smp_dev = chan->data;
 
 		memcpy(smp->local_pk, smp_dev->local_pk, 64);
-		memcpy(smp->local_sk, smp_dev->local_sk, 32);
 		memcpy(smp->lr, smp_dev->local_rand, 16);
 
 		if (smp_dev->debug_key)
@@ -1911,23 +1905,20 @@ static u8 sc_send_public_key(struct smp_chan *smp)
 
 	if (hci_dev_test_flag(hdev, HCI_USE_DEBUG_KEYS)) {
 		BT_DBG("Using debug keys");
+		if (set_ecdh_privkey(smp->tfm_ecdh, debug_sk))
+			return SMP_UNSPECIFIED;
 		memcpy(smp->local_pk, debug_pk, 64);
-		memcpy(smp->local_sk, debug_sk, 32);
 		set_bit(SMP_FLAG_DEBUG_KEY, &smp->flags);
 	} else {
 		while (true) {
-			/* Seed private key with random number */
-			get_random_bytes(smp->local_sk, 32);
-
-			/* Generate local key pair for Secure Connections */
-			if (generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk,
-					       smp->local_sk))
+			/* Generate key pair for Secure Connections */
+			if (generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk))
 				return SMP_UNSPECIFIED;
 
 			/* This is unlikely, but we need to check that
 			 * we didn't accidentially generate a debug key.
 			 */
-			if (crypto_memneq(smp->local_sk, debug_sk, 32))
+			if (crypto_memneq(smp->local_pk, debug_pk, 64))
 				break;
 		}
 	}
@@ -1935,7 +1926,6 @@ static u8 sc_send_public_key(struct smp_chan *smp)
 done:
 	SMP_DBG("Local Public Key X: %32phN", smp->local_pk);
 	SMP_DBG("Local Public Key Y: %32phN", smp->local_pk + 32);
-	SMP_DBG("Local Private Key:  %32phN", smp->local_sk);
 
 	smp_send_cmd(smp->conn, SMP_CMD_PUBLIC_KEY, 64, smp->local_pk);
 
@@ -2663,6 +2653,7 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb)
 	struct l2cap_chan *chan = conn->smp;
 	struct smp_chan *smp = chan->data;
 	struct hci_dev *hdev = hcon->hdev;
+	struct crypto_kpp *tfm_ecdh;
 	struct smp_cmd_pairing_confirm cfm;
 	int err;
 
@@ -2695,8 +2686,18 @@ static int smp_cmd_public_key(struct l2cap_conn *conn, struct sk_buff *skb)
 	SMP_DBG("Remote Public Key X: %32phN", smp->remote_pk);
 	SMP_DBG("Remote Public Key Y: %32phN", smp->remote_pk + 32);
 
-	if (!compute_ecdh_secret(smp->tfm_ecdh, smp->remote_pk, smp->local_sk,
-				 smp->dhkey))
+	/* Compute the shared secret on the same crypto tfm on which the private
+	 * key was set/generated.
+	 */
+	if (test_bit(SMP_FLAG_LOCAL_OOB, &smp->flags)) {
+		struct smp_dev *smp_dev = chan->data;
+
+		tfm_ecdh = smp_dev->tfm_ecdh;
+	} else {
+		tfm_ecdh = smp->tfm_ecdh;
+	}
+
+	if (compute_ecdh_secret(tfm_ecdh, smp->remote_pk, smp->dhkey))
 		return SMP_UNSPECIFIED;
 
 	SMP_DBG("DHKey %32phN", smp->dhkey);
@@ -3522,27 +3523,18 @@ void smp_unregister(struct hci_dev *hdev)
 
 #if IS_ENABLED(CONFIG_BT_SELFTEST_SMP)
 
-static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
-{
-	int i;
-
-	for (i = 0; i < ndigits; i++)
-		out[i] = __swab64(in[ndigits - 1 - i]);
-}
-
 static int __init test_debug_key(struct crypto_kpp *tfm_ecdh)
 {
-	u8 pk[64], sk[32];
+	u8 pk[64];
 	int err;
 
-	swap_digits((u64 *)debug_sk, (u64 *)sk, 4);
-
-	err = generate_ecdh_keys(tfm_ecdh, pk, sk);
+	err = set_ecdh_privkey(tfm_ecdh, debug_sk);
 	if (err)
 		return err;
 
-	if (crypto_memneq(sk, debug_sk, 32))
-		return -EINVAL;
+	err = generate_ecdh_public_key(tfm_ecdh, pk);
+	if (err)
+		return err;
 
 	if (crypto_memneq(pk, debug_pk, 64))
 		return -EINVAL;