null pointer dereference error in mtk_timer.c

null pointer dereference error in mtk_timer.c

[박용배]

Hello. My name is Yongbae Park.

I would like to report a possible null pointer dereference error at
mtk_timer_interrupt() in drivers/clocksource/mtk_timer.c (version:
3.19-rc5). The null pointer dereference error occurs if the interrupt
handler mtk_timer_interrupt() accesses evt->dev.event_handler (line
146) when evt->dev.event_handler is null and not defined by
mtk_timer_init().

mtk_timer_init() first registers mtk_timer_interrupt() as the
interrupt handler at line 227, and then defines the clockevent handler
at line 246. As a consequence, the interrupt handler can be executed
before the clockevent handler definition when an interrupt occurs
between line 227 and line 246. The detail error scenario is the
following:

183: static void __init mtk_timer_init(struct device_node *node) {
...
227: if (request_irq(evt->dev.irq, mtk_timer_interrupt,
228:           IRQF_TIMER | IRQF_IRQPOLL, "mtk_timer", evt)) {
...
------ An interrupt is fired and the interrupt handler is called -------
    140: static irqreturn_t mtk_timer_interrupt(int irq, void *dev_id)
    141: {
    142:   struct mtk_clock_event_device *evt = dev_id;
    143:
    144:   /* Acknowledge timer0 irq */
    145:   writel(GPT_IRQ_ACK(GPT_CLK_EVT), evt->gpt_base + GPT_IRQ_ACK_REG);
    146:   evt->dev.event_handler(&evt->dev); //evt->dev.event_handler
is not defined
    147:
    148:   return IRQ_HANDLED;
    149: }
------ The execution of the interrupt handler is finished ------
...
246: clockevents_config_and_register(&evt->dev, rate, 0x3,
247:             0xffffffff);

To resolve the problem, I think that the interrupt handler should be
registered after the clock handler registration.

For your information, I give you the references to similar issues from
the previous bug reports:
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=6bab4a8a1888729f17f4923cc5867e4674f66333
http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=da64c2a8dee66ca03f4f3e15d84be7bedf73db3d

Thank you.

Re: null pointer dereference error in mtk_timer.c

[Matthias Brugger]

Hi Yongbae,

2015-02-16 8:35 GMT+01:00 박용배 <yongbae2@gmail.com>:
> Hello. My name is Yongbae Park.
>
>
> I would like to report a possible null pointer dereference error at
> mtk_timer_interrupt() in drivers/clocksource/mtk_timer.c (version:
> 3.19-rc5). The null pointer dereference error occurs if the interrupt
> handler mtk_timer_interrupt() accesses evt->dev.event_handler (line 146)
> when evt->dev.event_handler is null and not defined by mtk_timer_init().
>
> mtk_timer_init() first registers mtk_timer_interrupt() as the interrupt
> handler at line 227, and then defines the clockevent handler at line 246. As
> a consequence, the interrupt handler can be executed before the clockevent
> handler definition when an interrupt occurs between line 227 and line 246.
> The detail error scenario is the following:
>
>
>
> 183: static void __init mtk_timer_init(struct device_node *node) {
>
> ...
>
> 227: if (request_irq(evt->dev.irq, mtk_timer_interrupt,
>
> 228:           IRQF_TIMER | IRQF_IRQPOLL, "mtk_timer", evt)) {
>
> ...
>
> ------ An interrupt is fired and the interrupt handler is called -------
>
>     140: static irqreturn_t mtk_timer_interrupt(int irq, void *dev_id)
>
>     141: {
>
>     142:   struct mtk_clock_event_device *evt = dev_id;
>
>     143:
>
>     144:   /* Acknowledge timer0 irq */
>
>     145:   writel(GPT_IRQ_ACK(GPT_CLK_EVT), evt->gpt_base +
> GPT_IRQ_ACK_REG);
>
>     146:   evt->dev.event_handler(&evt->dev); // evt->dev.event_handler is
> not defined
>
>     147:
>
>     148:   return IRQ_HANDLED;
>
>     149: }
>
> ------ The execution of the interrupt handler is finished ------
>
> ...
>
> 246: clockevents_config_and_register(&evt->dev, rate, 0x3,
>
> 247:             0xffffffff);
>
>
>
> To resolve the problem, I think that the interrupt handler should be
> registered after the clock handler registration.

Thanks for your hint. Actually there are two race conditions.
First we register an interrupt handler, before disabling all
interrupts by calling mtk_timer_global_reset (line 227).
An secondly we register clockevents after enabling the interrupts (line 246).

I will provide a patch for this.

Best regards,
Matthias

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