[bug report] media: allegro: possible NULL pointer dereference.

[Yuri Savinykh <s02190703@gse.cs.msu.ru>]

Hello,

At the moment of enabling irq handling:

3166     ret = devm_request_threaded_irq(&pdev->dev, irq,
3167                     allegro_hardirq,
3168                     allegro_irq_thread,
3169                     IRQF_SHARED, dev_name(&pdev->dev), dev);

there is still uninitialized field mbox_status of struct allegro_dev *dev.
If an interrupt occurs in the interval between the installation of the
interrupt handler and the initialization of this field, NULL pointer
dereference happens.

This field is dereferenced in the handler function without any check:

1801 static irqreturn_t allegro_irq_thread(int irq, void *data)
1802 {
1803     struct allegro_dev *dev = data;
1804
1805     allegro_mbox_notify(dev->mbox_status);


and then:

752 static void allegro_mbox_notify(struct allegro_mbox *mbox)
753 {
754     struct allegro_dev *dev = mbox->dev;

The initialization of the mbox_status field happens asynchronously in
allegro_fw_callback() via allegro_mcu_hw_init(). 

Is it guaranteed that an interrupt does not occur in this interval?
If it is not, is it better to move interrupt handler installation
after initialization of this field has been completed?

Found by Linux Driver Verification project (linuxtesting.org).