On Tue, Oct 24, 2017 at 6:30 AM, Bryan O'Donoghue
<pure.logic@xxxxxxxxxxxxxxxxx> wrote:
> On 24/10/17 14:14, Kees Cook wrote:
>>
>> On Tue, Oct 24, 2017 at 5:52 AM, Bryan O'Donoghue
>> <pure.logic@xxxxxxxxxxxxxxxxx> wrote:
>>>
>>> On 24/10/17 13:47, Kees Cook wrote:
>>>>
>>>>
>>>> On Tue, Oct 24, 2017 at 2:40 AM, Bryan O'Donoghue
>>>> <pure.logic@xxxxxxxxxxxxxxxxx> wrote:
>>>>>
>>>>>
>>>>> On 24/10/17 10:35, Bryan O'Donoghue wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 24/10/17 09:25, Kees Cook wrote:
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> In preparation for unconditionally passing the struct timer_list
>>>>>>> pointer
>>>>>>> to
>>>>>>> all timer callbacks, switch to using the new timer_setup() and
>>>>>>> from_timer()
>>>>>>> to pass the timer pointer explicitly.
>>>>>>>
>>>>>>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>>>>>>> Cc: "Bryan O'Donoghue" <pure.logic@xxxxxxxxxxxxxxxxx>
>>>>>>> Cc: Johan Hovold <johan@xxxxxxxxxx>
>>>>>>> Cc: Alex Elder <elder@xxxxxxxxxx>
>>>>>>> Cc: greybus-dev@xxxxxxxxxxxxxxxx
>>>>>>> Cc: devel@xxxxxxxxxxxxxxxxxxxx
>>>>>>> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
>>>>>>> ---
>>>>>>> drivers/staging/greybus/loopback.c | 14 ++++----------
>>>>>>> drivers/staging/greybus/operation.c | 7 +++----
>>>>>>> 2 files changed, 7 insertions(+), 14 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/staging/greybus/loopback.c
>>>>>>> b/drivers/staging/greybus/loopback.c
>>>>>>> index 08e255884206..045aaf81113a 100644
>>>>>>> --- a/drivers/staging/greybus/loopback.c
>>>>>>> +++ b/drivers/staging/greybus/loopback.c
>>>>>>> @@ -572,16 +572,11 @@ static void
>>>>>>> gb_loopback_async_operation_work(struct
>>>>>>> work_struct *work)
>>>>>>> gb_loopback_async_operation_put(op_async);
>>>>>>> }
>>>>>>> -static void gb_loopback_async_operation_timeout(unsigned long data)
>>>>>>> +static void gb_loopback_async_operation_timeout(struct timer_list
>>>>>>> *t)
>>>>>>> {
>>>>>>> - struct gb_loopback_async_operation *op_async;
>>>>>>> - u16 id = data;
>>>>>>> + struct gb_loopback_async_operation *op_async =
>>>>>>> + from_timer(op_async, t, timer);
>>>>>>> - op_async = gb_loopback_operation_find(id);
>>>>>>> - if (!op_async) {
>>>>>>> - pr_err("operation %d not found - time out ?\n", id);
>>>>>>> - return;
>>>>>>> - }
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> Hi Kees, you need to add
>>>>>>
>>>>>> gb_loopback_async_operation_get(op_async); when dropping the
>>>>>> gb_loopback_operation_find() call here.
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> Actually:
>>>>>
>>>>> spin_lock_irqsave(&gb_dev.lock, flags);
>>>>> gb_loopback_async_operation_get(op_async);
>>>>> spin_unlock_irqrestore(&gb_dev.lock, flags);
>>>>
>>>>
>>>> Shouldn't the get/put follow the lifetime of the timer running
>>>> instead? It shouldnt' be possible to free the op_async while the timer
>>>> is still pending/running.
>>>
>>>
>>> The timeout timer runs for an operation that never completed but on the
>>> regular "everything is good" path you end up doing
>>> del_timer_sync(&op_async->timer); so the timer doesn't run.
>>
>>
>> As far as I can tell, the get/put is already happening external to the
>> timer:
>>
>> gb_loopback_async_operation():
>> ...
>> op_async = kzalloc(sizeof(*op_async), GFP_KERNEL);
>> ...
>> INIT_WORK(&op_async->work, gb_loopback_async_operation_work);
>> kref_init(&op_async->kref);
>> ...
>> op_async->pending = true;
>> ...
>> ret = gb_operation_request_send(operation,
>>
>> gb_loopback_async_operation_callback,
>> 0,
>> GFP_KERNEL);
>> ...
>> timer_setup(&op_async->timer,
>> gb_loopback_async_operation_timeout, 0);
>> op_async->timer.expires = jiffies + gb->jiffy_timeout;
>> add_timer(&op_async->timer);
>>
>>
>> gb_loopback_async_operation_callback(): (run by operation)
>> ...
>> op_async->pending = false;
>> del_timer_sync(&op_async->timer);
>> gb_loopback_async_operation_put(op_async);
>>
>>
>> gb_loopback_async_operation_work(): (scheduled by timer)
>> ...
>> op_async->pending = false;
>> gb_loopback_async_operation_put(op_async);
>>
>
>
>> (Doing a get/put in the timer callback itself shouldn't be happening:
>> it must already be pinned in memory for the callback to run.)
>
>
> Both gb_loopback_async_operation_callback() and
> (gb_loopback_async_operation_timeout || gb_loopback_async_operation_work())
> can run in parallel so the get in the timer callback means we can let the
> timer stuff free-run w/r to gb_loopback_async_operation_callback() - take a
> reference indicating we still want that object and then let
> gb_loopback_async_operation_work() run.
Ah right, we're protecting the scheduled worker thread. I'll send a v2, thanks!
-Kees
--
Kees Cook
Pixel Security
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