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

Vulnerability Description

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().

References

• https://git.kernel.org/stable/c/19a98d56dfedafb25652bdb9cd48a4e73ceba702
• https://git.kernel.org/stable/c/90530e7214c8a04dcdde57502d93fa96af288c38
• https://git.kernel.org/stable/c/954fc9931f0aabf272b5674cf468affdd88d3a36
• https://git.kernel.org/stable/c/2a36b444cace9580380467fd1183bb5e85bcc80a
• https://git.kernel.org/stable/c/1be6f2b15f902c02e055ae0b419ca789200473c9