Hi Luiz, On 22.01.22 00:32, Luiz Augusto von Dentz wrote: > Hi Sönke, > > On Fri, Jan 21, 2022 at 3:18 PM Sönke Huster <soenke.huster@xxxxxxxxx> wrote: >> >> Hi Luiz, >> >> On 21.01.22 22:31, Luiz Augusto von Dentz wrote: >>> Hi Sönke, >>> >>> On Fri, Jan 21, 2022 at 10:22 AM Sönke Huster <soenke.huster@xxxxxxxxx> wrote: >>>> >>>> I just noticed that just checking for handle does not work, as obviously 0x0 could also be a handle value and therefore it can't be distinguished, whether it is not set yet or it is 0x0. >>> >>> Yep, we should probably check its state, check for state != BT_OPEN >>> since that is what hci_conn_add initialize the state. >>> >> >> I thought there are more valid connection states for the first HCI_CONNECTION_COMPLETE event, as it also occurs e.g. after an HCI_Create_Connection command, see Core 5.3 p.2170: >>> This event also indicates to the Host which issued the HCI_Create_Connection, HCI_Accept_- >>> Connection_Request, or HCI_Reject_Connection_Request command, and >>> then received an HCI_Command_Status event, if the issued command failed or >>> was successful. >> >> For example in hci_conn.c hci_acl_create_connection (which triggers a HCI_Create_Connection command as far as I understand), the state of the connection is changed to BT_CONNECT or BT_CONNECT2. >> But as I am quite new in the (Linux) Bluetooth world, I might have a wrong understanding of that. > > Yep, we would probably need a switch to capture which states are valid > and which are not or we initialize the handle with something outside > of the valid range of handles (0x0000 to 0x0EFF) so we can initialize > it to e.g. 0xffff (using something like define HCI_CONN_HANDLE_UNSET) > so we can really tell when it has been set or not. > I think the state switch is just possible if there is no possibility to change a connection state back into one of the accepted states. Unless changing the state back into an accepted state includes a call to "hci_conn_del_sysfs", as the real issue when getting a duplicate HCI_Create_Connection event is that device_add in hci_conn_add_sysfs is called twice for the same connection. There might be other issues as well in processing a duplicate event, but as far as I can see the bugs I trigger rely on multiple calls to device_add which lead in the long run to multiple user-after frees or null-pointer derefs. I tried to write that up in the bugzilla report here: https://bugzilla.kernel.org/show_bug.cgi?id=215497 When using something like HCI_CONN_HANDLE_UNSET, we need to make sure that everywhere where we receive a handle from an event and use it to set conn->handle, it is a valid one. Otherwise a hacked / malicious controller would just send multiple events for the invalid handle. What solution do you prefer? If you don't mind I'd like to try to create a patch. >>>> On 21.01.22 18:36, Soenke Huster wrote: >>>>> When a HCI_CONNECTION_COMPLETE event is received multiple times >>>>> for the same handle, the device is registered multiple times which leads >>>>> to memory corruptions. Therefore, consequent events for a single >>>>> connection are ignored. >>>>> >>>>> The conn->state can hold different values so conn->handle is >>>>> checked to detect whether a connection is already set up. >>>>> >>>>> Buglink: https://bugzilla.kernel.org/show_bug.cgi?id=215497 >>>>> Signed-off-by: Soenke Huster <soenke.huster@xxxxxxxxx> >>>>> --- >>>>> This fixes the referenced bug and several use-after-free issues I discovered. >>>>> I tagged it as RFC, as I am not 100% sure if checking the existence of the >>>>> handle is the correct approach, but to the best of my knowledge it must be >>>>> set for the first time in this function for valid connections of this event, >>>>> therefore it should be fine. >>>>> >>>>> net/bluetooth/hci_event.c | 11 +++++++++++ >>>>> 1 file changed, 11 insertions(+) >>>>> >>>>> diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c >>>>> index 681c623aa380..71ccb12c928d 100644 >>>>> --- a/net/bluetooth/hci_event.c >>>>> +++ b/net/bluetooth/hci_event.c >>>>> @@ -3106,6 +3106,17 @@ static void hci_conn_complete_evt(struct hci_dev *hdev, void *data, >>>>> } >>>>> } >>>>> >>>>> + /* The HCI_Connection_Complete event is only sent once per connection. >>>>> + * Processing it more than once per connection can corrupt kernel memory. >>>>> + * >>>>> + * As the connection handle is set here for the first time, it indicates >>>>> + * whether the connection is already set up. >>>>> + */ >>>>> + if (conn->handle) { >>>>> + bt_dev_err(hdev, "Ignoring HCI_Connection_Complete for existing connection"); >>>>> + goto unlock; >>>>> + } >>>>> + >>>>> if (!ev->status) { >>>>> conn->handle = __le16_to_cpu(ev->handle); >>>>> >>> >>> >>> >> >> Best >> Sönke > > >
