bluetooth: host: Add workaround for USB HCI controllers

This commit adds a new option CONFIG_BT_SMP_USB_HCI_CTLR_WORKAROUND
to support USB HCI controllers that sometimes send out-of-order HCI
events and ACL Data due to using different USB endpoints.

Enabling this option will make the master role not require the
encryption-change event to be received before accepting
key-distribution data.

It opens up for a potential vulnerability as the master cannot detect
if the keys are distributed over an encrypted link.

Fixes: zephyrproject-rtos#22086

Signed-off-by: François Delawarde <fnde@oticon.com>

subsys/bluetooth/host/Kconfig

@@ -350,6 +350,19 @@ config BT_SMP_ALLOW_UNAUTH_OVERWRITE
 	  to create a new bond the old bond has to be explicitly deleted with
 	  bt_unpair.
 
+config BT_SMP_USB_HCI_CTLR_WORKAROUND
+	bool "Workaround for USB HCI controller out-of-order events"
+	depends on BT_TESTING
+	help
+	  This option enables support for USB HCI controllers that sometimes
+	  send out-of-order HCI events and ACL Data due to using different USB
+	  endpoints.
+	  Enabling this option will make the master role not require the
+	  encryption-change event to be received before accepting key-distribution
+	  data.
+	  It opens up for a potential vulnerability as the master cannot detect
+	  if the keys are distributed over an encrypted link.
+
 config BT_FIXED_PASSKEY
 	bool "Use a fixed passkey for pairing"
 	help

subsys/bluetooth/host/smp.c

@@ -2311,6 +2311,19 @@ static u8_t legacy_pairing_random(struct bt_smp *smp)
 
 		atomic_set_bit(smp->flags, SMP_FLAG_ENC_PENDING);
 
+		if (IS_ENABLED(CONFIG_BT_SMP_USB_HCI_CTLR_WORKAROUND)) {
+			if (smp->remote_dist & BT_SMP_DIST_ENC_KEY) {
+				atomic_set_bit(&smp->allowed_cmds,
+					       BT_SMP_CMD_ENCRYPT_INFO);
+			} else if (smp->remote_dist & BT_SMP_DIST_ID_KEY) {
+				atomic_set_bit(&smp->allowed_cmds,
+					       BT_SMP_CMD_IDENT_INFO);
+			} else if (smp->remote_dist & BT_SMP_DIST_SIGN) {
+				atomic_set_bit(&smp->allowed_cmds,
+					       BT_SMP_CMD_SIGNING_INFO);
+			}
+		}
+
 		return 0;
 	}
 
@@ -3999,6 +4012,17 @@ static u8_t smp_dhkey_check(struct bt_smp *smp, struct net_buf *buf)
 		}
 
 		atomic_set_bit(smp->flags, SMP_FLAG_ENC_PENDING);
+
+		if (IS_ENABLED(CONFIG_BT_SMP_USB_HCI_CTLR_WORKAROUND)) {
+			if (smp->remote_dist & BT_SMP_DIST_ID_KEY) {
+				atomic_set_bit(&smp->allowed_cmds,
+					       BT_SMP_CMD_IDENT_INFO);
+			} else if (smp->remote_dist & BT_SMP_DIST_SIGN) {
+				atomic_set_bit(&smp->allowed_cmds,
+					       BT_SMP_CMD_SIGNING_INFO);
+			}
+		}
+
 		return 0;
 	}
 
@@ -5319,6 +5343,11 @@ int bt_smp_init(void)
 		return -ENOENT;
 	}
 
+	if (IS_ENABLED(CONFIG_BT_SMP_USB_HCI_CTLR_WORKAROUND)) {
+		BT_WARN("BT_SMP_USB_HCI_CTLR_WORKAROUND is enabled, which "
+			"exposes a security vulnerability!");
+	}
+
 	BT_DBG("LE SC %s", sc_supported ? "enabled" : "disabled");
 
 	bt_pub_key_gen(&pub_key_cb);