Re: [BUG] tty: serial: mxs-auart: possible concurrency use-after-free bugs in mxs_auart_dma_exit_channel()

[Jia-Ju Bai]

On 2019/1/7 16:52, Greg KH wrote:
> On Mon, Jan 07, 2019 at 04:47:43PM +0800, Jia-Ju Bai wrote:
> > The driver functions mxs_auart_settermios(), dma_rx_callback() and dma_tx_callback() can be concurrently executed.
> >
> > In Linux 4.19:
> >
> > mxs_auart_settermios
> >    mxs_auart_dma_exit
> >      mxs_auart_dma_exit_channel
> >        line 918: kfree(s->tx_dma_buf);
> >        line 919: kfree(s->rx_dma_buf);
> >
> > dma_rx_callback
> >    line 862: tty_insert_flip_string(port, s->rx_dma_buf, count);
> >    mxs_auart_dma_prep_rx
> >      line 890: sg_init_one(sgl, s->rx_dma_buf, UART_XMIT_SIZE);
> >
> > dma_tx_callback
> >    mxs_auart_tx_chars
> >      line 590: void *buffer = s->tx_dma_buf;
> >      mxs_auart_dma_tx
> >        line 566: sg_init_one(sgl, s->tx_dma_buf, size);
> >
> > Thus, possible concurrency use-after-free bugs may occur.
> >
> > These possible bugs are found by a static analysis tool written by myself and my manual code review.
> Care to send a patch to fix up this issue?

I would like to, but I do not know how to fix these bugs properly...
There is no lock and lock-related function call in 
drivers/tty/serial/mxs-auart.c.
Thus, we may need to introduce a new lock in this source file.
What is your opinion?


Best wishes,
Jia-Ju Bai