Re: [PATCH] usb: core: Fix possible memleak in usb_add_gadget

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Sep 05, 2021 at 05:16:36PM +0200, Florian Faber wrote:
> Greg,
> 
> On 9/5/21 4:56 PM, Greg KH wrote:
> > On Sat, Sep 04, 2021 at 05:34:29PM +0200, Florian Faber wrote:
> > > The memory for the udc structure allocated via kzalloc in line 1295 is not
> > > freed in the error handling code, leading to a memory leak in case of an
> > > error.
> > > 
> > > Singed-off-by: Florian Faber <faber@faberman.de>
> > > 
> > > ---
> > >   drivers/usb/gadget/udc/core.c | 2 ++
> > >   1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/usb/gadget/udc/core.c b/drivers/usb/gadget/udc/core.c
> > > index 14fdf918ecfe..a1270a44855a 100644
> > > --- a/drivers/usb/gadget/udc/core.c
> > > +++ b/drivers/usb/gadget/udc/core.c
> > > @@ -1346,6 +1346,8 @@ int usb_add_gadget(struct usb_gadget *gadget)
> > > 
> > >    err_put_udc:
> > >   	put_device(&udc->dev);
> > > +	kfree(udc);
> > > +	gadget->udc = NULL;
> > > 
> > >    error:
> > >   	return ret;
> > > -- 
> > > 2.33.0
> > > 
> > > Flo
> > > -- 
> > > Machines can do the work, so people have time to think.
> > 
> > Did you test this?  I think you will find that you just caused a
> > use-after-free :(
> 
> Correct, please forget about this patch.
> 
> This 'leak' was found by Klocwork and seemed plausible at first oversight.
> Sorry for wasting your time and not checking it further.

What is "Klockwork"?  How can it miss the reference counted logic that
all drivers use in the kernel?

> > Please read the documentation for device_initialize() for why this is
> > not the correct thing to do here.
> 
> I know now :) It was a bit counter intuitive that two different methods are
> used for memory allocation and freeing.

The joy of reference counted stuff, sorry.

thanks,

greg k-h