Re: [PATCH 1/2] serial: sprd: Assign sprd_port after initialized to avoid wrong access

[Baolin Wang]

On 7/11/2023 10:57 AM, Chunyan Zhang wrote:
> On Mon, 10 Jul 2023 at 17:57, Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> > On 7/10/2023 4:03 PM, Chunyan Zhang wrote:
> > > The global pointer 'sprd_port' maybe not zero when sprd_probe returns
> > > fail, that is a risk for sprd_port to be accessed afterward, and will
> > > lead unexpected errors.
> > >
> > > For example:
> > >
> > > There're two UART ports, UART1 is used for console and configured in kernel
> > > command line, i.e. "console=";
> > >
> > > The UART1 probe fail and the memory allocated to sprd_port[1] was released,
> > > but sprd_port[1] was not set to NULL;
> >
> > IMO, we should just set sprd_port[1] to be NULL, which seems simpler?
>
> This patch just does like this indeed, in the label of 'clean_port'.
> Adding a local variable instead of using global pointer (sprd_port[])
> to store the virtual address allocated for sprd_port can avoid
> overmany goto labels.
>
> > > In UART2 probe, the same virtual address was allocated to sprd_port[2],
> > > and UART2 probe process finally will go into sprd_console_setup() to
> > > register UART1 as console since it is configured as preferred console
> > > (filled to console_cmdline[]), but the console parameters (sprd_port[1])
> > > actually belongs to UART2.
> >
> > I'm confusing why the console parameters belongs to UART2? Since the
> > console_cmdline[] will specify the serial index, that belongs to UART1.
>
> The same virtual address stored in sprd_port[1] was reallocated to
> sprd_port[2] after the UART1 probe returned failure.

After more thinking, I understood your case. :)

But I see a nit in this patch, you added a 'clean_port' label to clear 
the resource for the fail-probe-port instead of sprd_remove(), however 
sprd_remove() will call sprd_rx_free_buf() to free the DMA buffer 
originally. I know the 2nd patch will add it back, but patch 1 is not 
git-bisect safe, right?

So I think you should also add sprd_rx_free_buf() under the 'clean_port' 
label in patch 1, then patch 2 moves the sprd_rx_free_buf() to the 
correct place.

> > Please correct me if I miss something.
> >
> > > So move the sprd_port[] assignment to where the port already initialized
> > > can avoid the above issue.
> > >
> > > Fixes: b7396a38fb28 ("tty/serial: Add Spreadtrum sc9836-uart driver support")
> > > Signed-off-by: Chunyan Zhang <chunyan.zhang@xxxxxxxxxx>
> > > ---
> > >    drivers/tty/serial/sprd_serial.c | 24 ++++++++++++++++--------
> > >    1 file changed, 16 insertions(+), 8 deletions(-)
> > >
> > > diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> > > index b58f51296ace..942808517393 100644
> > > --- a/drivers/tty/serial/sprd_serial.c
> > > +++ b/drivers/tty/serial/sprd_serial.c
> > > @@ -1106,7 +1106,7 @@ static bool sprd_uart_is_console(struct uart_port *uport)
> > >    static int sprd_clk_init(struct uart_port *uport)
> > >    {
> > >        struct clk *clk_uart, *clk_parent;
> > > -     struct sprd_uart_port *u = sprd_port[uport->line];
> > > +     struct sprd_uart_port *u = container_of(uport, struct sprd_uart_port, port);
> > >
> > >        clk_uart = devm_clk_get(uport->dev, "uart");
> > >        if (IS_ERR(clk_uart)) {
> > > @@ -1149,22 +1149,22 @@ static int sprd_probe(struct platform_device *pdev)
> > >    {
> > >        struct resource *res;
> > >        struct uart_port *up;
> > > +     struct sprd_uart_port *sport;
> > >        int irq;
> > >        int index;
> > >        int ret;
> > >
> > >        index = of_alias_get_id(pdev->dev.of_node, "serial");
> > > -     if (index < 0 || index >= ARRAY_SIZE(sprd_port)) {
> > > +     if (index < 0 || index >= UART_NR_MAX) {
> > >                dev_err(&pdev->dev, "got a wrong serial alias id %d\n", index);
> > >                return -EINVAL;
> > >        }
> > >
> > > -     sprd_port[index] = devm_kzalloc(&pdev->dev, sizeof(*sprd_port[index]),
> > > -                                     GFP_KERNEL);
> > > -     if (!sprd_port[index])
> > > +     sport = devm_kzalloc(&pdev->dev, sizeof(*sport), GFP_KERNEL);
> > > +     if (!sport)
> > >                return -ENOMEM;
> > >
> > > -     up = &sprd_port[index]->port;
> > > +     up = &sport->port;
> > >        up->dev = &pdev->dev;
> > >        up->line = index;
> > >        up->type = PORT_SPRD;
> > > @@ -1195,7 +1195,7 @@ static int sprd_probe(struct platform_device *pdev)
> > >         * Allocate one dma buffer to prepare for receive transfer, in case
> > >         * memory allocation failure at runtime.
> > >         */
> > > -     ret = sprd_rx_alloc_buf(sprd_port[index]);
> > > +     ret = sprd_rx_alloc_buf(sport);
> > >        if (ret)
> > >                return ret;
> > >
> > > @@ -1208,12 +1208,20 @@ static int sprd_probe(struct platform_device *pdev)
> > >        }
> > >        sprd_ports_num++;
> > >
> > > +     sprd_port[index] = sport;
> > > +
> > >        ret = uart_add_one_port(&sprd_uart_driver, up);
> > >        if (ret)
> > > -             sprd_remove(pdev);
> > > +             goto clean_port;
> > >
> > >        platform_set_drvdata(pdev, up);
> > >
> > > +     return 0;
> > > +
> > > +clean_port:
> > > +     sprd_port[index] = NULL;
> > > +     sprd_ports_num--;
> > > +     uart_unregister_driver(&sprd_uart_driver);
> > >        return ret;
> > >    }