linux-kernel - Re: [PATCH -next] serial: 8250: fix return error code in serial8250_request_std

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Date:   Mon, 27 Jun 2022 14:08:43 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yi Yang <yiyang13@...wei.com>
Cc:     jirislaby@...nel.org, ilpo.jarvinen@...ux.intel.com,
        andy.shevchenko@...il.com, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH -next] serial: 8250: fix return error code in
 serial8250_request_std_resource()

On Mon, Jun 20, 2022 at 03:20:25PM +0800, Yi Yang wrote:
> If port->mapbase = NULL in serial8250_request_std_resource() , it need
> return a error code instead of 0. If uart_set_info() fail to request new
> regions by serial8250_request_std_resource() but the return value of
> serial8250_request_std_resource() is 0, that The system will mistakenly
> considers that port resources are successfully applied for. A null
> pointer reference is triggered when the port resource is later invoked.
> 
> The problem can also be triggered with the following simple program:
> ----------
>   #include <stdio.h>
>   #include <sys/types.h>
>   #include <sys/stat.h>
>   #include <fcntl.h>
>   #include <sys/ioctl.h>
>   #include <unistd.h>
>   #include <errno.h>
> 
>   struct serial_struct {
>       int type;
>       int line;
>       unsigned int    port;
>       int irq;
>       int flags;
>       int xmit_fifo_size;
>       int custom_divisor;
>       int baud_base;
>       unsigned short  close_delay;
>       char    io_type;
>       char    reserved_char[1];
>       int hub6;
>       unsigned short  closing_wait; /* time to wait before closing */
>       unsigned short  closing_wait2; /* no longer used... */
>       unsigned char   *iomem_base;
>       unsigned short  iomem_reg_shift;
>       unsigned int    port_high;
>       unsigned long   iomap_base; /* cookie passed into ioremap */
>   };
> 
>   struct serial_struct str;
> 
>   int main(void)
>   {
>       open("/dev/ttyS0", O_RDWR);
>       ioctl(fd, TIOCGSERIAL, &str);
>       str.iomem_base = 0;
>       ioctl(fd, TIOCSSERIAL, str);
>       return 0;
>   }
> ----------
> 
> Signed-off-by: Yi Yang <yiyang13@...wei.com>
> ---
>  drivers/tty/serial/8250/8250_port.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index 3e3d784aa628..e1cefa97bdeb 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -2961,8 +2961,10 @@ static int serial8250_request_std_resource(struct uart_8250_port *up)
>  	case UPIO_MEM32BE:
>  	case UPIO_MEM16:
>  	case UPIO_MEM:
> -		if (!port->mapbase)
> +		if (!port->mapbase) {
> +			ret = -EFAULT;

This not a memory fault, that only gets returned for failures when
copying to/from userspace.

Please return -EINVAL or something like that.

thanks,

greg k-h