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

From: Jia-Ju Bai
Date: Mon Jan 07 2019 - 04:04:02 EST

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:

line 918: kfree(s->tx_dma_buf);
line 919: kfree(s->rx_dma_buf);

line 862: tty_insert_flip_string(port, s->rx_dma_buf, count);
line 890: sg_init_one(sgl, s->rx_dma_buf, UART_XMIT_SIZE);

line 590: void *buffer = s->tx_dma_buf;
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