[PATCH] usb: core: Unregister device on component_add() failure

[PATCH] usb: core: Unregister device on component_add() failure

[Fabio M. De Francesco]

Commit 8c67d06f3fd9 ("usb: Link the ports to the connectors they are
attached to") creates a link to the USB Type-C connector for every new
port that is added when possible. If component_add() fails,
usb_hub_create_port_device() prints a warning but does not unregister
the device and does not return errors to the callers.

Syzbot reported a "WARNING in component_del()".

Fix this issue in usb_hub_create_port_device by calling device_unregister()
and returning the errors from component_add().

Reported-by: syzbot+60df062e1c41940cae0f@syzkaller.appspotmail.com
Fixes: 8c67d06f3fd9 ("usb: Link the ports to the connectors they are attached to")
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
---
 drivers/usb/core/port.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index c2bbf97a79be..8455b235976a 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -605,8 +605,11 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
 	find_and_link_peer(hub, port1);
 
 	retval = component_add(&port_dev->dev, &connector_ops);
-	if (retval)
+	if (retval) {
 		dev_warn(&port_dev->dev, "failed to add component\n");
+		device_unregister(&port_dev->dev);
+		return retval;
+	}
 
 	/*
 	 * Enable runtime pm and hold a refernce that hub_configure()
-- 
2.34.1

Re: [PATCH] usb: core: Unregister device on component_add() failure

[Heikki Krogerus]

On Tue, Feb 08, 2022 at 06:00:48PM +0100, Fabio M. De Francesco wrote:
> Commit 8c67d06f3fd9 ("usb: Link the ports to the connectors they are
> attached to") creates a link to the USB Type-C connector for every new
> port that is added when possible. If component_add() fails,
> usb_hub_create_port_device() prints a warning but does not unregister
> the device and does not return errors to the callers.
> 
> Syzbot reported a "WARNING in component_del()".
> 
> Fix this issue in usb_hub_create_port_device by calling device_unregister()
> and returning the errors from component_add().
> 
> Reported-by: syzbot+60df062e1c41940cae0f@syzkaller.appspotmail.com
> Fixes: 8c67d06f3fd9 ("usb: Link the ports to the connectors they are attached to")
> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> ---
>  drivers/usb/core/port.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
> index c2bbf97a79be..8455b235976a 100644
> --- a/drivers/usb/core/port.c
> +++ b/drivers/usb/core/port.c
> @@ -605,8 +605,11 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
>  	find_and_link_peer(hub, port1);
>  
>  	retval = component_add(&port_dev->dev, &connector_ops);
> -	if (retval)
> +	if (retval) {
>  		dev_warn(&port_dev->dev, "failed to add component\n");
> +		device_unregister(&port_dev->dev);
> +		return retval;

You didn't remove the peer links. Either remove them here separately,
or alternatively you can also just shuffle the code so that you only
create those links after the component_add() call:

diff --git a/drivers/usb/core/port.c b/drivers/usb/core/port.c
index c2bbf97a79bec..d5bc36ca5b1f7 100644
--- a/drivers/usb/core/port.c
+++ b/drivers/usb/core/port.c
@@ -602,11 +602,14 @@ int usb_hub_create_port_device(struct usb_hub *hub, int port1)
                return retval;
        }
 
-       find_and_link_peer(hub, port1);
-
        retval = component_add(&port_dev->dev, &connector_ops);
-       if (retval)
+       if (retval) {
                dev_warn(&port_dev->dev, "failed to add component\n");
+               device_unregister(&port_dev->dev);
+               return retval;
+       }
+
+       find_and_link_peer(hub, port1);
 
        /*
         * Enable runtime pm and hold a refernce that hub_configure()

thanks,

-- 
heikki

Re: [PATCH] usb: core: Unregister device on component_add() failure

[Fabio M. De Francesco]

On mercoled? 9 febbraio 2022 15:00:09 CET Heikki Krogerus wrote:
> On Tue, Feb 08, 2022 at 06:00:48PM +0100, Fabio M. De Francesco wrote:
> > Commit 8c67d06f3fd9 ("usb: Link the ports to the connectors they are
> > attached to") creates a link to the USB Type-C connector for every new
> > port that is added when possible. If component_add() fails,
> > usb_hub_create_port_device() prints a warning but does not unregister
> > the device and does not return errors to the callers.
> > 
> > Syzbot reported a "WARNING in component_del()".
> > 
> > Fix this issue in usb_hub_create_port_device by calling device_unregister()
> > and returning the errors from component_add().
> > 
> > Reported-by: syzbot+60df062e1c41940cae0f@syzkaller.appspotmail.com
> > Fixes: 8c67d06f3fd9 ("usb: Link the ports to the connectors they are attached to")
> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com>
> > ---
> >  drivers/usb/core/port.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > [...]
> >
> You didn't remove the peer links. Either remove them here separately,
> or alternatively you can also just shuffle the code so that you only
> create those links after the component_add() call:
>
> [...]
> 

Hello Heikki,

Thanks for your review and suggestion. I think that I'll use the second of the
two possible solutions (shuffle the code).

I had to spend some time to understand the code of usb_hub_create_port_device(),
component_add() and component_del(). Unfortunately, the USB core is very far from
the usual things I look at or care of. Therefore I missed that find_and_link_peer()
does some work that must be either unwound or simply postponed. I agree with you 
that the latter is the best solution.

I need some minutes to submit v2.

Again, thanks,

Fabio

> thanks,
> 
> -- 
> heikki
>