CVE-2023-53094

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

tty: serial: fsl_lpuart: fix race on RX DMA shutdown

From time to time DMA completion can come in the middle of DMA shutdown:

<process ctx>: <IRQ>:

lpuart32_shutdown()

lpuart_dma_shutdown()

del_timer_sync()

lpuart_dma_rx_complete()

lpuart_copy_rx_to_tty()

mod_timer()

lpuart_dma_rx_free()

When the timer fires a bit later, sport->dma_rx_desc is NULL:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000004

pc : lpuart_copy_rx_to_tty+0xcc/0x5bc

lr : lpuart_timer_func+0x1c/0x2c

Call trace:

lpuart_copy_rx_to_tty

lpuart_timer_func

call_timer_fn

__run_timers.part.0

run_timer_softirq

__do_softirq

__irq_exit_rcu

irq_exit

handle_domain_irq

gic_handle_irq

call_on_irq_stack

do_interrupt_handler

...

To fix this fold del_timer_sync() into lpuart_dma_rx_free() after

dmaengine_terminate_sync() to make sure timer will not be re-started in

lpuart_copy_rx_to_tty() <= lpuart_dma_rx_complete().