Re: [PATCH 1/1] NFC: Fix possible memory corruption when handling SHDLC I-Frame commands

[Suren Baghdasaryan <surenb@google.com>]

On Tue, Aug 14, 2018 at 2:49 PM, Kees Cook <keescook@chromium.org> wrote:
> On Tue, Aug 14, 2018 at 1:55 PM, Suren Baghdasaryan <surenb@google.com> wrote:
>> On Tue, Aug 14, 2018 at 1:33 PM, Kees Cook <keescook@chromium.org> wrote:
>>> On Tue, Aug 14, 2018 at 1:26 PM, Suren Baghdasaryan <surenb@google.com> wrote:
>>>> On Tue, Aug 14, 2018 at 9:57 AM, Suren Baghdasaryan <surenb@google.com> wrote:
>>>>> On Tue, Aug 14, 2018 at 2:54 AM, Dan Carpenter <dan.carpenter@oracle.com> wrote:
>>>>>> Thanks.  This is great.  I'm so glad these are finally getting fixed.
>>>>>>
>>>>>> Do we need to fix nfc_hci_msg_rx_work() and nfc_hci_recv_from_llc() as
>>>>>> well?  In nfc_hci_recv_from_llc() we allow pipe to be NFC_HCI_FRAGMENT
>>>>>> (0x7f) so that's one element beyond the end of the array and the
>>>>>> NFC_HCI_HCP_RESPONSE isn't checked.
>>>>>>
>>>>>> Also nci_hci_msg_rx_work() and nci_hci_data_received_cb() use
>>>>>> NCI_HCP_MSG_GET_PIPE() so those could be off by one.
>>>>>
>>>>> Good point. From hci.h:
>>>>>
>>>>> /*
>>>>>  * According to specification 102 622 chapter 4.4 Pipes,
>>>>>  * the pipe identifier is 7 bits long.
>>>>>  */
>>>>> #define NFC_HCI_MAX_PIPES 127
>>>>>
>>>>> And then:
>>>>>
>>>>> struct nfc_hci_dev {
>>>>>   ...
>>>>>   struct nfc_hci_pipe pipes[NFC_HCI_MAX_PIPES];
>>>>>   ...
>>>>> }
>>>>>
>>>>> I think the correct fix would be to change it to:
>>>>>
>>>>>   struct nfc_hci_pipe pipes[NFC_HCI_MAX_PIPES + 1];
>>>>>
>>>>> What do you think?
>>>>>

Actually, after looking more closely, NFC_HCI_MAX_PIPES is always used
as the number of supported pipes and not as the max pipe ID, so the
right fix would be:

-#define NFC_HCI_MAX_PIPES 127
+#define NFC_HCI_MAX_PIPES 128

I would prefer to rename it into NFC_HCI_PIPE_COUNT but don't want to
introduce unnecessary churn for one-line change, so will keep the
name. Will post a separate fix for this shortly.

>>>>
>>>> Just to be clear, this would fix the problem Dan described in his
>>>> reply and it should be implemented in a separate patch. The original
>>>> fix is still valid.
>>>
>>> I think you could merge the fixes into a single patch.
>>
>> Couple reasons I would prefer to keep them separate:
>> - I feel that descriptions for these two issues should be different
>> and it's easier if we don't mix them up
>> - This one is already merged into Android kernels, so would be easier
>> to introduce the second fix separately
>> - I would like to give credit to people who noticed the problem (in
>> this case those are different people)
>>
>> However if more people think we should fix both issues in the same
>> patch I'll happily do that.
>> Thanks!
>
> If it's already landed separately somewhere else, then yeah, 2 patches
> sounds good. No objection either way from me!
>
> -Kees
>
> --
> Kees Cook
> Pixel Security