null pointer dereference error in timer-sun5i.c

[박용배 <yongbae2@gmail.com>]

Hello. My name is Yongbae Park.


I would like to report a possible null pointer dereference error at
sun5i_timer_interrupt() in drivers/clocksource/timer-sun5i.c (version:
3.19-rc5). The null pointer dereference error occurs if the interrupt
handler sun5i_timer_interrupt() accesses evt->event_handler (line 128)
when evt->event_handler is null and not defined by sun5i_timer_init().

sun5i_timer_init() first registers sun5i_timer_interrupt() as the
interrupt handler at line 181, and then defines the clockevent handler
at line 192. As a consequence, the interrupt handler can be executed
before the clockevent handler definition when an interrupt occurs
between line 181 and line 192. The detail error scenario is the
following:

145: static void __init sun5i_timer_init(struct device_node *node) {
...
181: ret = setup_irq(irq, &sun5i_timer_irq);d
...
------ An interrupt is fired and the interrupt handler is called -------
    123: static irqreturn_t sun5i_timer_interrupt(int irq, void *dev_id)
    124: {
    125:   struct clock_event_device *evt = (struct clock_event_device *)dev_id;
    126:
    127:   writel(0x1, timer_base + TIMER_IRQ_ST_REG);
    128:   evt->event_handler(evt); // evt->event_handler is not defined
    129:
    130:   return IRQ_HANDLED;
    131: }
------ The execution of the interrupt handler is finished ------
...
192: clockevents_config_and_register(&sun5i_clockevent, rate,
193:             TIMER_SYNC_TICKS, 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.