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.)
-Kees
--
Kees Cook
Pixel Security
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