Re: [PATCH v4] um: vector: Fix exception handling in vector_eth_configure()

[Anton Ivanov]

On 19/08/2023 22:01, Richard Weinberger wrote:
> ----- Ursprüngliche Mail -----
> > The resource cleanup was incomplete in the implementation
> > of the function "vector_eth_configure".
> > Thus replace the jump target
> > "out_undo_user_init" by "out_free_netdev".
> > Delate the orphan function "out_undo_user_init"
> >
> > PATCH v1-v3: Modify the patch format.
> >
> > Signed-off-by: Minjie Du <duminjie@xxxxxxxx>
> > ---
> > arch/um/drivers/vector_kern.c | 4 +---
> > 1 file changed, 1 insertion(+), 3 deletions(-)
> >
> > diff --git a/arch/um/drivers/vector_kern.c b/arch/um/drivers/vector_kern.c
> > index 131b7cb29..7ae6ab8df 100644
> > --- a/arch/um/drivers/vector_kern.c
> > +++ b/arch/um/drivers/vector_kern.c
> > @@ -1646,7 +1646,7 @@ static void vector_eth_configure(
> > 	err = register_netdevice(dev);
> > 	rtnl_unlock();
> > 	if (err)
> > -		goto out_undo_user_init;
> > +		goto out_free_netdev;
> >
> > 	spin_lock(&vector_devices_lock);
> > 	list_add(&device->list, &vector_devices);
> > @@ -1654,8 +1654,6 @@ static void vector_eth_configure(
> >
> > 	return;
> >
> > -out_undo_user_init:
> > -	return;
>
> I don't think this is correct.
> vector_eth_configure() cannot communicate the failure since it is of type void.
> So, vector_remove() will run and will call unregister_netdev(). That can cause a double-free.

vector_remove() will be called only once per device. It checks if the 
device is in the device list and if it is not - bails. If it is in the 
list it removes it from there and calls unregister_netdev() after that.

So, unless I am missing something, there is no harm here - unregister 
will not be called for a device that failed to register, because the 
list is updated only if the device has registered successfully.

However, on second read - if register fails, the current code leaks a 
*device which was alloc-ed in the beginning of configure. So even if we 
skip free_netdev, which invokes remove we still need to free that *device.

> Thanks,
> //richard

--
Anton R. Ivanov
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