2014-01-02 13:53:13

by David Vrabel

Subject: Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device call

On 19/12/13 15:03, Levente Kurusa wrote:
> This is required so that we give up the last reference to the device.
>
> Signed-off-by: Levente Kurusa <[email protected]>
> ---
> drivers/xen/xenbus/xenbus_probe.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> index 3c0a74b..4abb9ee 100644
> --- a/drivers/xen/xenbus/xenbus_probe.c
> +++ b/drivers/xen/xenbus/xenbus_probe.c
> @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
>
> /* Register with generic device framework. */
> err = device_register(&xendev->dev);
> - if (err)
> + if (err) {
> + put_device(&xendev->dev);
> goto fail;
> + }
>
> return 0;
> fail:

There is a kfree(xendev) here so this introduces a double-free.

David

2014-01-06 10:00:50

by Ian Campbell

Subject: Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device call

On Thu, 2014-01-02 at 13:53 +0000, David Vrabel wrote:
> On 19/12/13 15:03, Levente Kurusa wrote:
> > This is required so that we give up the last reference to the device.
> >
> > Signed-off-by: Levente Kurusa <[email protected]>
> > ---
> > drivers/xen/xenbus/xenbus_probe.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> > index 3c0a74b..4abb9ee 100644
> > --- a/drivers/xen/xenbus/xenbus_probe.c
> > +++ b/drivers/xen/xenbus/xenbus_probe.c
> > @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
> >
> > /* Register with generic device framework. */
> > err = device_register(&xendev->dev);
> > - if (err)
> > + if (err) {
> > + put_device(&xendev->dev);
> > goto fail;
> > + }
> >
> > return 0;
> > fail:
>
> There is a kfree(xendev) here so this introduces a double-free.

How? put_device doesn't touch xendev itself, does it? It just drops the
ref on the dev member which is not separately dynamically allocated and
so not freed either.

Ian.

2014-01-06 11:00:39

by David Vrabel

Subject: Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device call

On 06/01/14 10:00, Ian Campbell wrote:
> On Thu, 2014-01-02 at 13:53 +0000, David Vrabel wrote:
>> On 19/12/13 15:03, Levente Kurusa wrote:
>>> This is required so that we give up the last reference to the device.
>>>
>>> Signed-off-by: Levente Kurusa <[email protected]>
>>> ---
>>> drivers/xen/xenbus/xenbus_probe.c | 4 +++-
>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
>>> index 3c0a74b..4abb9ee 100644
>>> --- a/drivers/xen/xenbus/xenbus_probe.c
>>> +++ b/drivers/xen/xenbus/xenbus_probe.c
>>> @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
>>>
>>> /* Register with generic device framework. */
>>> err = device_register(&xendev->dev);
>>> - if (err)
>>> + if (err) {
>>> + put_device(&xendev->dev);
>>> goto fail;
>>> + }
>>>
>>> return 0;
>>> fail:
>>
>> There is a kfree(xendev) here so this introduces a double-free.
>
> How? put_device doesn't touch xendev itself, does it? It just drops the
> ref on the dev member which is not separately dynamically allocated and
> so not freed either.

Releasing all references to the struct device frees the containing
structure via xenbus->dev.release. i.e., xenbus_dev_release() which does
kfree(xendev).

David

2014-01-06 11:10:04

by Ian Campbell

Subject: Re: [Xen-devel] [PATCH 26/38] xen: xenbus: add missing put_device call

On Mon, 2014-01-06 at 11:00 +0000, David Vrabel wrote:
> On 06/01/14 10:00, Ian Campbell wrote:
> > On Thu, 2014-01-02 at 13:53 +0000, David Vrabel wrote:
> >> On 19/12/13 15:03, Levente Kurusa wrote:
> >>> This is required so that we give up the last reference to the device.
> >>>
> >>> Signed-off-by: Levente Kurusa <[email protected]>
> >>> ---
> >>> drivers/xen/xenbus/xenbus_probe.c | 4 +++-
> >>> 1 file changed, 3 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> >>> index 3c0a74b..4abb9ee 100644
> >>> --- a/drivers/xen/xenbus/xenbus_probe.c
> >>> +++ b/drivers/xen/xenbus/xenbus_probe.c
> >>> @@ -465,8 +465,10 @@ int xenbus_probe_node(struct xen_bus_type *bus,
> >>>
> >>> /* Register with generic device framework. */
> >>> err = device_register(&xendev->dev);
> >>> - if (err)
> >>> + if (err) {
> >>> + put_device(&xendev->dev);
> >>> goto fail;
> >>> + }
> >>>
> >>> return 0;
> >>> fail:
> >>
> >> There is a kfree(xendev) here so this introduces a double-free.
> >
> > How? put_device doesn't touch xendev itself, does it? It just drops the
> > ref on the dev member which is not separately dynamically allocated and
> > so not freed either.
>
> Releasing all references to the struct device frees the containing
> structure via xenbus->dev.release. i.e., xenbus_dev_release() which does
> kfree(xendev).

Ooh, twisty, well spotted ;-)

Ian.