null pointer dereference error in time-efm32.c

[ëìë]

Hello. My name is Yongbae Park.

I would like to report a possible null pointer dereference error at
efm32_clock_event_handler() in drivers/clocksource/time-efm32.c
(version: 3.19-rc5). The null pointer dereference error occurs if the
interrupt handler efm32_clock_event_handler() accesses
ddata->evtdev.event_handler (line 106) when
ddata->evtdev.event_handler is null and not defined by
efm32_clockevent_init().

efm32_clockevent_init() first registers efm32_clock_event_handler() as
the interrupt handler at line 228, and then defines the clockevent
handler at line 230. As a consequence, the interrupt handler can be
executed before the clockevent handler definition when an interrupt
occurs between line 228 and line 230. The detail error scenario is the
following:

186: static int __init efm32_clockevent_init(struct device_node *np) {
...
228: setup_irq(irq, &efm32_clock_event_irq);
...
------ An interrupt is fired and the interrupt handler is called -------
    100: static irqreturn_t efm32_clock_event_handler(int irq, void *dev_id)
    101: {
    102:   struct efm32_clock_event_ddata *ddata = dev_id;
    103:
    104:   writel_relaxed(TIMERn_IRQ_UF, ddata->base + TIMERn_IFC);
    105:
    106:   ddata->evtdev.event_handler(&ddata->evtdev); //
ddata->evtdev.event_handler is not defined
    107:
    108:   return IRQ_HANDLED;
    109: }
------ The execution of the interrupt handler is finished ------
...
230: clockevents_config_and_register(&clock_event_ddata.evtdev,
231:             DIV_ROUND_CLOSEST(rate, 1024),
232:             0xf, 0xffff);

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.
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