Bluetooth: Add selftest for ECDH key generation

Since the ECDH key generation takes a different path, it needs to be
tested as well. For this generate the public debug key from the private
debug key and compare both.

This also moves the seeding of the private key into the SMP calling code
to allow for easier re-use of the ECDH key generation helper.
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>

net/bluetooth/ecdh_helper.c

@@ -22,7 +22,6 @@
  */
 #include "ecdh_helper.h"
 
-#include <linux/random.h>
 #include <linux/scatterlist.h>
 #include <crypto/kpp.h>
 #include <crypto/ecdh.h>
@@ -181,8 +180,6 @@ bool generate_ecdh_keys(u8 public_key[64], u8 private_key[32])
 		if (tries++ >= max_tries)
 			goto free_all;
 
-		get_random_bytes(private_key, 32);
-
 		/* Set private Key */
 		p.key = (char *)private_key;
 		crypto_ecdh_encode_key(buf, buf_len, &p);

net/bluetooth/smp.c

@@ -569,6 +569,9 @@ int smp_generate_oob(struct hci_dev *hdev, u8 hash[16], u8 rand[16])
 		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 */
 			if (!generate_ecdh_keys(smp->local_pk, smp->local_sk))
 				return -EIO;
@@ -1895,6 +1898,9 @@ static u8 sc_send_public_key(struct smp_chan *smp)
 		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->local_pk, smp->local_sk))
 				return SMP_UNSPECIFIED;
@@ -3483,6 +3489,32 @@ 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(void)
+{
+	u8 pk[64], sk[32];
+
+	swap_digits((u64 *)debug_sk, (u64 *)sk, 4);
+
+	if (!generate_ecdh_keys(pk, sk))
+		return -EINVAL;
+
+	if (memcmp(sk, debug_sk, 32))
+		return -EINVAL;
+
+	if (memcmp(pk, debug_pk, 64))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int __init test_ah(struct crypto_cipher *tfm_aes)
 {
 	const u8 irk[16] = {
@@ -3738,6 +3770,12 @@ static int __init run_selftests(struct crypto_cipher *tfm_aes,
 
 	calltime = ktime_get();
 
+	err = test_debug_key();
+	if (err) {
+		BT_ERR("debug_key test failed");
+		goto done;
+	}
+
 	err = test_ah(tfm_aes);
 	if (err) {
 		BT_ERR("smp_ah test failed");