[PATCH v2] Bluetooth: skip invalid hci_sync_conn_complete_evt

From: Desmond Cheong Zhi Xi
Date: Wed Jul 28 2021 - 03:52:09 EST


Syzbot reported a corrupted list in kobject_add_internal [1]. This
happens when multiple HCI_EV_SYNC_CONN_COMPLETE event packets with
status 0 are sent for the same HCI connection. This causes us to
register the device more than once which corrupts the kset list.

As this is forbidden behavior, we add a check for whether we're
trying to process the same HCI_EV_SYNC_CONN_COMPLETE event multiple
times for one connection. If that's the case, the event is invalid, so
we report an error that the device is misbehaving, and ignore the
packet.

Link: https://syzkaller.appspot.com/bug?extid=66264bf2fd0476be7e6c [1]
Reported-by: syzbot+66264bf2fd0476be7e6c@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+66264bf2fd0476be7e6c@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
---

v1 -> v2:
- Added more comments to explain the reasoning behind the new check, and
a bt_dev_err message upon detecting the invalid event. As suggested by
Marcel Holtmann.

net/bluetooth/hci_event.c | 16 ++++++++++++++++
1 file changed, 16 insertions(+)

diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
index 016b2999f219..a6df4f9d2c23 100644
--- a/net/bluetooth/hci_event.c
+++ b/net/bluetooth/hci_event.c
@@ -4373,6 +4373,22 @@ static void hci_sync_conn_complete_evt(struct hci_dev *hdev,

switch (ev->status) {
case 0x00:
+ /* The synchronous connection complete event should only be
+ * sent once per new connection. Receiving a successful
+ * complete event when the connection status is already
+ * BT_CONNECTED means that the device is misbehaving and sent
+ * multiple complete event packets for the same new connection.
+ *
+ * Registering the device more than once can corrupt kernel
+ * memory, hence upon detecting this invalid event, we report
+ * an error and ignore the packet.
+ */
+ if (conn->state == BT_CONNECTED) {
+ bt_dev_err(hdev,
+ "received multiple HCI_EV_SYNC_CONN_COMPLETE events with status 0 for conn %p",
+ conn);
+ goto unlock;
+ }
conn->handle = __le16_to_cpu(ev->handle);
conn->state = BT_CONNECTED;
conn->type = ev->link_type;
--
2.25.1