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SubjectRe: [PATCH v2] ppdev: fix double-free of pp->pdev->name
On Thu, Nov 10, 2016 at 02:18:12PM +0100, Arnd Bergmann wrote:
> On Sunday, October 30, 2016 11:19:24 PM CET Jann Horn wrote:
> > diff --git a/drivers/char/ppdev.c b/drivers/char/ppdev.c
> > index d23368874710..6af1ce04b3da 100644
> > --- a/drivers/char/ppdev.c
> > +++ b/drivers/char/ppdev.c
> > @@ -748,10 +748,7 @@ static int pp_release(struct inode *inode, struct file *file)
> > }
> >
> > if (pp->pdev) {
> > - const char *name = pp->pdev->name;
> > -
> > parport_unregister_device(pp->pdev);
> > - kfree(name);
> > pp->pdev = NULL;
> > pr_debug(CHRDEV "%x: unregistered pardevice\n", minor);
> > }
> >
>
> I took a closer look at this and found that we also leak the name
> that is passed in register_device() in the same file:
>
> name = kasprintf(GFP_KERNEL, CHRDEV "%x", minor);
> ...
> pdev = parport_register_dev_model(port, name, &ppdev_cb, minor);
>
> parport_register_dev_model() copies the name using kstrdup() and
> we should really free it after parport_register_dev_model().

yes. I missed that while converting the driver to use device model.
Thanks. I will send a patch to fix this tonight.

>
> It's not a huge problem, just leaking a few bytes of memory, but
> the extra kfree() probably came from this confusion.

No, it was the old code which was not in the device-model. The old code
uses parport_register_device() which just uses the same string that is
passed to it and so it was freed while releasing the device.

Regards
Sudip

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