Hi Sönke,
On Fri, Jan 21, 2022 at 3:18 PM Sönke Huster <[email protected]> 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 <[email protected]> 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.
> >> 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 <[email protected]>
> >>> ---
> >>> 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
--
Luiz Augusto von Dentz
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 <[email protected]> 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 <[email protected]> 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 <[email protected]>
>>>>> ---
>>>>> 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
>
>
>