Bluetooth: hci_event: Fix using memcmp when comparing keys

memcmp is not consider safe to use with cryptographic secrets:

 'Do  not  use memcmp() to compare security critical data, such as
 cryptographic secrets, because the required CPU time depends on the
 number of equal bytes.'

While usage of memcmp for ZERO_KEY may not be considered a security
critical data, it can lead to more usage of memcmp with pairing keys
which could introduce more security problems.

Fixes: 455c2ff0 ("Bluetooth: Fix BR/EDR out-of-band pairing with only initiator data")
Fixes: 33155c4a ("Bluetooth: hci_event: Ignore NULL link key")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>

net/bluetooth/hci_event.c

@@ -26,6 +26,8 @@
 /* Bluetooth HCI event handling. */
 
 #include <asm/unaligned.h>
+#include <linux/crypto.h>
+#include <crypto/algapi.h>
 
 #include <net/bluetooth/bluetooth.h>
 #include <net/bluetooth/hci_core.h>
@@ -4754,7 +4756,7 @@ static void hci_link_key_notify_evt(struct hci_dev *hdev, void *data,
 		goto unlock;
 
 	/* Ignore NULL link key against CVE-2020-26555 */
-	if (!memcmp(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
+	if (!crypto_memneq(ev->link_key, ZERO_KEY, HCI_LINK_KEY_SIZE)) {
 		bt_dev_dbg(hdev, "Ignore NULL link key (ZERO KEY) for %pMR",
 			   &ev->bdaddr);
 		hci_disconnect(conn, HCI_ERROR_AUTH_FAILURE);
@@ -5294,8 +5296,8 @@ static u8 bredr_oob_data_present(struct hci_conn *conn)
 		 * available, then do not declare that OOB data is
 		 * present.
 		 */
-		if (!memcmp(data->rand256, ZERO_KEY, 16) ||
-		    !memcmp(data->hash256, ZERO_KEY, 16))
+		if (!crypto_memneq(data->rand256, ZERO_KEY, 16) ||
+		    !crypto_memneq(data->hash256, ZERO_KEY, 16))
 			return 0x00;
 
 		return 0x02;
@@ -5305,8 +5307,8 @@ static u8 bredr_oob_data_present(struct hci_conn *conn)
 	 * not supported by the hardware, then check that if
 	 * P-192 data values are present.
 	 */
-	if (!memcmp(data->rand192, ZERO_KEY, 16) ||
-	    !memcmp(data->hash192, ZERO_KEY, 16))
+	if (!crypto_memneq(data->rand192, ZERO_KEY, 16) ||
+	    !crypto_memneq(data->hash192, ZERO_KEY, 16))
 		return 0x00;
 
 	return 0x01;