iio: accel: fxls8962af: Fix use after free in fxls8962af_fifo_flush

In the Linux kernel, the following vulnerability has been resolved:

iio: accel: fxls8962af: Fix use after free in fxls8962af_fifo_flush

fxls8962af_fifo_flush() uses indio_dev->active_scan_mask (with

iio_for_each_active_channel()) without making sure the indio_dev

stays in buffer mode.

There is a race if indio_dev exits buffer mode in the middle of the

interrupt that flushes the fifo. Fix this by calling

synchronize_irq() to ensure that no interrupt is currently running when

disabling buffer mode.

Unable to handle kernel NULL pointer dereference at virtual address 00000000 when read

[...]

_find_first_bit_le from fxls8962af_fifo_flush+0x17c/0x290

fxls8962af_fifo_flush from fxls8962af_interrupt+0x80/0x178

fxls8962af_interrupt from irq_thread_fn+0x1c/0x7c

irq_thread_fn from irq_thread+0x110/0x1f4

irq_thread from kthread+0xe0/0xfc

kthread from ret_from_fork+0x14/0x2c