On Mon, Jun 20, 2022 at 10:53:24AM +0300, Ilpo Järvinen wrote:
> On Mon, 20 Jun 2022, 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;
> > }
>
> With admin priviledges I guess?
>
> > ----------
> >
> > Signed-off-by: Yi Yang <yiyang13@xxxxxxxxxx>
> > ---
> > 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;
> > break;
> > + }
> >
> > if (!request_mem_region(port->mapbase, size, "serial")) {
> > ret = -EBUSY;
> >
>
> I recall reading somewhere that somebody more knowledgeful than me noted
> that this interface has many ways to shoot oneself in the foot if one
> really wants to which is why some things are limited to admin only.
> I cannot seem to find that a reference to that now though.
Yes, what could go wrong with allowing userspace to specify memory
locations that a uart might be located at :)
This stuff should all be "locked down" for any system with untrusted
users.
thanks,
greg k-h
