[v1] comedi: dt2815: add hardware detection to prevent crash

[PATCH] comedi: dt2815: add hardware detection to prevent crash

Posted by Deepanshu Kartikey 3 weeks, 3 days ago

The dt2815 driver crashes when attached to I/O ports without actual
hardware present. This occurs because syzkaller or users can attach
the driver to arbitrary I/O addresses via COMEDI_DEVCONFIG ioctl.

When no hardware exists at the specified port, inb() operations return
0xff (floating bus), but outb() operations can trigger page faults due
to undefined behavior, especially under race conditions:

  BUG: unable to handle page fault for address: 000000007fffff90
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  RIP: 0010:dt2815_attach+0x6e0/0x1110

Add hardware detection by reading the status register before attempting
any write operations. If the read returns 0xff, assume no hardware is
present and fail the attach with -ENODEV. This prevents crashes from
outb() operations on non-existent hardware.

Reported-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=72f94b474d6e50b71ffc
Tested-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 drivers/comedi/drivers/dt2815.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/comedi/drivers/dt2815.c b/drivers/comedi/drivers/dt2815.c
index 03ba2fd18a21..7c642860f127 100644
--- a/drivers/comedi/drivers/dt2815.c
+++ b/drivers/comedi/drivers/dt2815.c
@@ -175,6 +175,18 @@ static int dt2815_attach(struct comedi_device *dev, struct comedi_devconfig *it)
 		    ? current_range_type : voltage_range_type;
 	}
 
+	/*
+	 * Check if hardware is present before attempting any I/O operations.
+	 * Reading 0xff from status register typically indicates no hardware
+	 * on the bus (floating bus reads as all 1s).
+	 */
+	if (inb(dev->iobase + DT2815_STATUS) == 0xff) {
+		dev_err(dev->class_dev,
+			"No hardware detected at I/O base 0x%lx\n",
+			dev->iobase);
+		return -ENODEV;
+	}
+
 	/* Init the 2815 */
 	outb(0x00, dev->iobase + DT2815_STATUS);
 	for (i = 0; i < 100; i++) {
-- 
2.43.0

Re: [PATCH] comedi: dt2815: add hardware detection to prevent crash

Posted by Deepanshu Kartikey 2 weeks, 5 days ago

On Mon, Mar 9, 2026 at 4:19 PM Deepanshu Kartikey <kartikey406@gmail.com> wrote:
>
> The dt2815 driver crashes when attached to I/O ports without actual
> hardware present. This occurs because syzkaller or users can attach
> the driver to arbitrary I/O addresses via COMEDI_DEVCONFIG ioctl.
>
> When no hardware exists at the specified port, inb() operations return
> 0xff (floating bus), but outb() operations can trigger page faults due
> to undefined behavior, especially under race conditions:
>
>   BUG: unable to handle page fault for address: 000000007fffff90
>   #PF: supervisor write access in kernel mode
>   #PF: error_code(0x0002) - not-present page
>   RIP: 0010:dt2815_attach+0x6e0/0x1110
>
> Add hardware detection by reading the status register before attempting
> any write operations. If the read returns 0xff, assume no hardware is
> present and fail the attach with -ENODEV. This prevents crashes from
> outb() operations on non-existent hardware.
>
> Reported-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=72f94b474d6e50b71ffc
> Tested-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
> Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
> Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> ---
>  drivers/comedi/drivers/dt2815.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/comedi/drivers/dt2815.c b/drivers/comedi/drivers/dt2815.c
> index 03ba2fd18a21..7c642860f127 100644
> --- a/drivers/comedi/drivers/dt2815.c
> +++ b/drivers/comedi/drivers/dt2815.c
> @@ -175,6 +175,18 @@ static int dt2815_attach(struct comedi_device *dev, struct comedi_devconfig *it)
>                     ? current_range_type : voltage_range_type;
>         }
>
> +       /*
> +        * Check if hardware is present before attempting any I/O operations.
> +        * Reading 0xff from status register typically indicates no hardware
> +        * on the bus (floating bus reads as all 1s).
> +        */
> +       if (inb(dev->iobase + DT2815_STATUS) == 0xff) {
> +               dev_err(dev->class_dev,
> +                       "No hardware detected at I/O base 0x%lx\n",
> +                       dev->iobase);
> +               return -ENODEV;
> +       }
> +
>         /* Init the 2815 */
>         outb(0x00, dev->iobase + DT2815_STATUS);
>         for (i = 0; i < 100; i++) {
> --
> 2.43.0
>


Hi Greg,

Gentle ping on this patch. This patch was submitted on 26th jan 2026.
It. It is  Reviewed-by: Ian Abbott <abbotti@mev.co.uk>

Subject: [PATCH] comedi: dt2815: add hardware
detection to prevent crash
Link: [https://lore.kernel.org/all/20260126070458.10974-1-kartikey406@gmail.com/T/]

Let me know if any changes required.

Thanks

Re: [PATCH] comedi: dt2815: add hardware detection to prevent crash

Posted by Deepanshu Kartikey 2 days, 20 hours ago

On Sun, Mar 15, 2026 at 7:48 AM Deepanshu Kartikey
<kartikey406@gmail.com> wrote:
>
> On Mon, Mar 9, 2026 at 4:19 PM Deepanshu Kartikey <kartikey406@gmail.com> wrote:
> >
> > The dt2815 driver crashes when attached to I/O ports without actual
> > hardware present. This occurs because syzkaller or users can attach
> > the driver to arbitrary I/O addresses via COMEDI_DEVCONFIG ioctl.
> >
> > When no hardware exists at the specified port, inb() operations return
> > 0xff (floating bus), but outb() operations can trigger page faults due
> > to undefined behavior, especially under race conditions:
> >
> >   BUG: unable to handle page fault for address: 000000007fffff90
> >   #PF: supervisor write access in kernel mode
> >   #PF: error_code(0x0002) - not-present page
> >   RIP: 0010:dt2815_attach+0x6e0/0x1110
> >
> > Add hardware detection by reading the status register before attempting
> > any write operations. If the read returns 0xff, assume no hardware is
> > present and fail the attach with -ENODEV. This prevents crashes from
> > outb() operations on non-existent hardware.
> >
> > Reported-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=72f94b474d6e50b71ffc
> > Tested-by: syzbot+72f94b474d6e50b71ffc@syzkaller.appspotmail.com
> > Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
> > Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
> > ---
> >  drivers/comedi/drivers/dt2815.c | 12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/comedi/drivers/dt2815.c b/drivers/comedi/drivers/dt2815.c
> > index 03ba2fd18a21..7c642860f127 100644
> > --- a/drivers/comedi/drivers/dt2815.c
> > +++ b/drivers/comedi/drivers/dt2815.c
> > @@ -175,6 +175,18 @@ static int dt2815_attach(struct comedi_device *dev, struct comedi_devconfig *it)
> >                     ? current_range_type : voltage_range_type;
> >         }
> >
> > +       /*
> > +        * Check if hardware is present before attempting any I/O operations.
> > +        * Reading 0xff from status register typically indicates no hardware
> > +        * on the bus (floating bus reads as all 1s).
> > +        */
> > +       if (inb(dev->iobase + DT2815_STATUS) == 0xff) {
> > +               dev_err(dev->class_dev,
> > +                       "No hardware detected at I/O base 0x%lx\n",
> > +                       dev->iobase);
> > +               return -ENODEV;
> > +       }
> > +
> >         /* Init the 2815 */
> >         outb(0x00, dev->iobase + DT2815_STATUS);
> >         for (i = 0; i < 100; i++) {
> > --
> > 2.43.0
> >
>
>
Hi Greg,
Gentle ping on this patch  . I submitted this patch on 26th jan 2026.
It is reviewed by : Reviewed-by: Ian Abbott <abbotti@mev.co.uk>

Please let me know if anything else required to get it merged

Thanks

Deepanshu