[PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Greg Kroah-Hartman]

When an error happens in mctp_usb_probe() the reference count on the usb
interface structure needs to be properly dropped as it was incremented
earlier in the function.

Cc: Jeremy Kerr <jk@codeconstruct.com.au>
Cc: Matt Johnston <matt@codeconstruct.com.au>
Cc: stable <stable@kernel.org>
Assisted-by: gkh_clanker_2000
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/net/mctp/mctp-usb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
index ef860cfc629f..eef17ae89298 100644
--- a/drivers/net/mctp/mctp-usb.c
+++ b/drivers/net/mctp/mctp-usb.c
@@ -355,6 +355,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
 	usb_free_urb(dev->tx_urb);
 	usb_free_urb(dev->rx_urb);
 	free_netdev(netdev);
+	usb_put_dev(dev->usbdev);
 	return rc;
 }
 
-- 
2.53.0

Re: [PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Jeremy Kerr]

Hi Greg,

> When an error happens in mctp_usb_probe() the reference count on the usb
> interface structure needs to be properly dropped as it was incremented
> earlier in the function.

Looks good, thanks for the fix.

Acked-by: Jeremy Kerr <jk@codeconstruct.com.au>

Cheers,


Jeremy

Re: [PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Jeremy Kerr]

Hi Greg,

On a second look:

> diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
> index ef860cfc629f..eef17ae89298 100644
> --- a/drivers/net/mctp/mctp-usb.c
> +++ b/drivers/net/mctp/mctp-usb.c
> @@ -355,6 +355,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
>         usb_free_urb(dev->tx_urb);
>         usb_free_urb(dev->rx_urb);
>         free_netdev(netdev);
> +       usb_put_dev(dev->usbdev);
>         return rc;
>  }

Should we not do the usb_put_dev() before the free_netdev()?

Given we're in NETREG_UNINITIALIZED state, we're likely to be
immediately freeing netdev there, which includes the netdev_priv data,
ie., dev.

Cheers,


Jeremy

Re: [PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Greg Kroah-Hartman]

On Tue, Feb 24, 2026 at 09:50:09AM +0800, Jeremy Kerr wrote:
> Hi Greg,
> 
> On a second look:
> 
> > diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
> > index ef860cfc629f..eef17ae89298 100644
> > --- a/drivers/net/mctp/mctp-usb.c
> > +++ b/drivers/net/mctp/mctp-usb.c
> > @@ -355,6 +355,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
> >         usb_free_urb(dev->tx_urb);
> >         usb_free_urb(dev->rx_urb);
> >         free_netdev(netdev);
> > +       usb_put_dev(dev->usbdev);
> >         return rc;
> >  }
> 
> Should we not do the usb_put_dev() before the free_netdev()?

Why?  The usb_put_dev() doesn't really do anything, except for the fact
that you have to do it because you did a usb_get_dev() earlier.  In
reality, no USB driver needs to call get/put on a usb device at all,
that is a bad pattern I made years ago for no good reason, sorry about
that.

I really should just sweep the tree to fix that up one of these days,
odds are a coccinelle script can do that...

> Given we're in NETREG_UNINITIALIZED state, we're likely to be
> immediately freeing netdev there, which includes the netdev_priv data,
> ie., dev.

That's great, but again, the usb device will still be around as the usb
core ensures that for the lifetime of probe/remove, the device will be
there with a reference.  So there's no real reason to put it anywhere in
this list, other than last as that mirrors when this was grabbed, right?

thanks,

greg k-h

Re: [PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Jeremy Kerr]

Hi Greg,

> > > diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
> > > index ef860cfc629f..eef17ae89298 100644
> > > --- a/drivers/net/mctp/mctp-usb.c
> > > +++ b/drivers/net/mctp/mctp-usb.c
> > > @@ -355,6 +355,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
> > >         usb_free_urb(dev->tx_urb);
> > >         usb_free_urb(dev->rx_urb);
> > >         free_netdev(netdev);
> > > +       usb_put_dev(dev->usbdev);
> > >         return rc;
> > >  }
> > 
> > Should we not do the usb_put_dev() before the free_netdev()?
> 
> Why?  The usb_put_dev() doesn't really do anything, except for the fact
> that you have to do it because you did a usb_get_dev() earlier.

More that the dev-> dereference may be invalid at that point, since the
netdev (and hence dev) has been free_netdev()-ed.

Cheers,


Jeremy

Re: [PATCH net] net: mctp: usb: properly drop the usb interface on probe error

[Greg Kroah-Hartman]

On Tue, Feb 24, 2026 at 02:31:03PM +0800, Jeremy Kerr wrote:
> Hi Greg,
> 
> > > > diff --git a/drivers/net/mctp/mctp-usb.c b/drivers/net/mctp/mctp-usb.c
> > > > index ef860cfc629f..eef17ae89298 100644
> > > > --- a/drivers/net/mctp/mctp-usb.c
> > > > +++ b/drivers/net/mctp/mctp-usb.c
> > > > @@ -355,6 +355,7 @@ static int mctp_usb_probe(struct usb_interface *intf,
> > > >         usb_free_urb(dev->tx_urb);
> > > >         usb_free_urb(dev->rx_urb);
> > > >         free_netdev(netdev);
> > > > +       usb_put_dev(dev->usbdev);
> > > >         return rc;
> > > >  }
> > > 
> > > Should we not do the usb_put_dev() before the free_netdev()?
> > 
> > Why?  The usb_put_dev() doesn't really do anything, except for the fact
> > that you have to do it because you did a usb_get_dev() earlier.
> 
> More that the dev-> dereference may be invalid at that point, since the
> netdev (and hence dev) has been free_netdev()-ed.

Argh, I missed that, yes, you are right, let me make a v2 of this,
thanks for the review!

greg k-h