linux-kernel - Re: [PATCH V3 1/2] serial: sprd: Assign sprd_port after initialized to avoid wrong access

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Date:   Tue, 25 Jul 2023 15:49:15 +0800
From:   Chunyan Zhang <zhang.lyra@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Chunyan Zhang <chunyan.zhang@...soc.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Orson Zhai <orsonzhai@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 1/2] serial: sprd: Assign sprd_port after initialized
 to avoid wrong access

On Tue, 25 Jul 2023 at 14:50, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Tue, Jul 25, 2023 at 02:40:52PM +0800, Chunyan Zhang wrote:
> > The global pointer 'sprd_port' may not zero when sprd_probe returns
> > failure, that is a risk for sprd_port to be accessed afterward, and
> > may lead to unexpected errors.
> >
> > For example:
> >
> > There are two UART ports, UART1 is used for console and configured in
> > kernel command line, i.e. "console=";
> >
> > The UART1 probe failed and the memory allocated to sprd_port[1] was
> > released, but sprd_port[1] was not set to NULL;
> >
> > 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])
> > belong to UART2.
> >
> > 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@...soc.com>
> > ---
> > V3:
> > - Call uart_unregister_driver() only when the 'sprd_ports_num' decreases to 0;
> > - Add calling sprd_rx_free_buf() instread of sprd_remove() under clean_up lable.
> >
> > V2:
> > - Leave sprd_remove() to keep the unrelated code logic the same.
> > ---
> >  drivers/tty/serial/sprd_serial.c | 25 +++++++++++++++++--------
> >  1 file changed, 17 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/tty/serial/sprd_serial.c b/drivers/tty/serial/sprd_serial.c
> > index b58f51296ace..fc1377029021 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);
>
> Now that you are not allocaing the sprd_port[] pointers, shouldn't you
> also remove that variable entirely?

sprd_console_write() and sprd_console_setup() [1] also need sprd_port[].

So, this driver still needs to allocate the buffer for sprd_port[],
the change is using a local variable instead of allocating directly to
the global pointer.

[1] https://elixir.bootlin.com/linux/v6.5-rc1/source/drivers/tty/serial/sprd_serial.c#L1000

Thanks,
Chunyan