Hi Chi Yuan,
On Fri, May 17, 2024 at 02:31:50PM +0800, ChiYuan Huang wrote:
> Hi, Sakari:
>
> Thanks for your reply.
> If any misunderstanding, please correct me.
>
> On Thu, May 16, 2024 at 10:42:05AM +0000, Sakari Ailus wrote:
> > Hi Chi Yuan,
> >
> > On Wed, May 08, 2024 at 10:51:49AM +0800, cy_huang@xxxxxxxxxxx wrote:
> > > From: ChiYuan Huang <cy_huang@xxxxxxxxxxx>
> > >
> > > In v4l2_async_create_ancillary_links(), if v4l2 async notifier is
> > > created from v4l2 device, the v4l2 flash subdev async binding will enter
> > > the logic to create media link. Due to the subdev of notifier is NULL,
> > > this will cause NULL pointer to access the subdev entity. Therefore, add
> > > the check to bypass it.
> > >
> > > Fixes: aa4faf6eb271 ("media: v4l2-async: Create links during v4l2_async_match_notify()")
> > > Signed-off-by: ChiYuan Huang <cy_huang@xxxxxxxxxxx>
> > > ---
> > > Hi,
> > >
> > > I'm trying to bind the v4l2 subdev for flashlight testing. It seems
> > > some logic in v4l2 asynd binding is incorrect.
> > >
> > > From the change, I modified vim2m as the test driver to bind mt6370 flashlight.
> > >
> > > Here's the backtrace log.
> > >
> > > vim2m soc:vim2m: bound [white:flash-2]
> > > Unable to handle kernel NULL pointer dereference at virtual address 0000000000000058
> > > ......skipping
> > > Call trace:
> > > media_create_ancillary_link+0x48/0xd8 [mc]
> > > v4l2_async_match_notify+0x17c/0x208 [v4l2_async]
> > > v4l2_async_register_subdev+0xb8/0x1d0 [v4l2_async]
> >
> > There's something wrong obviously somewhere but wherea?
> >
> In vim2m driver, I added v4l2_async_nf_init -> v4l2_async_nf_add_fwnode_remote ->
> v4l2_async_nf_register.
>
> From the async flow, in notifier complete ops to create v4l-subdevX node for the
> specified subdev.
> > A sub-notifier does have a sub-device after the notifier initialisation.
>
> Why? Are you saying to the notifier can only be used for subdev and subdev binding,
> not v4l2 and subdev binding?
>
> But to create v4l-subdevX, the key is only v4l2 device and its needed subdev.
>
> > Maybe the initialisation does not happen in the right order?
> AFAIK, Async flow can solve the probe order and makes the user no need to care
> the probe order.
>
> From the stacktrace, I'm pretty sure it's not the probe order issue.
> >
> > > __v4l2_flash_init.part.0+0x3b4/0x4b0 [v4l2_flash_led_class]
> > > v4l2_flash_init+0x28/0x48 [v4l2_flash_led_class]
> > > mt6370_led_probe+0x348/0x690 [leds_mt6370_flash]
> > >
> > > After tracing the code, it will let the subdev labeled as F_LENS or
> > > F_FLASH function to create media link. To prevent the NULL pointer
> > > issue, the simplest way is add a check when 'n->sd' is NULL and bypass
> > > the later media link creataion.
> > > ---
> > > drivers/media/v4l2-core/v4l2-async.c | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/drivers/media/v4l2-core/v4l2-async.c b/drivers/media/v4l2-core/v4l2-async.c
> > > index 3ec323bd528b..9d3161c51954 100644
> > > --- a/drivers/media/v4l2-core/v4l2-async.c
> > > +++ b/drivers/media/v4l2-core/v4l2-async.c
> > > @@ -324,6 +324,9 @@ static int v4l2_async_create_ancillary_links(struct v4l2_async_notifier *n,
> > > sd->entity.function != MEDIA_ENT_F_FLASH)
> > > return 0;
> > >
> > > + if (!n->sd)
> > > + return 0;
> >
> > This isn't the right fix: the ancillary link won't be created as a result.
> >
> Due to the notifier is created by v4l2 device not subdev, this 'n->sd' is NULL.
> The NULL 'n->sd' will be referenced by the next flow 'media_create_ancillary_link'.
Ah, right. I took a new look into the code and agree this is a problem.
This probably hasn't been hit previously as the root notifier driver tends
not to have any lens or flash devices.
I'd change the commit message slightly:
--------8<-------------
In v4l2_async_create_ancillary_links(), ancillary links are created for
lens and flash sub-devices. These are sub-device to sub-device links and if
the async notifier is related to a V4L2 device, the source sub-device of
the ancillary link is NULL, leading to a NULL pointer dereference. Check
the notifier's sd field is non-NULL in v4l2_async_create_ancillary_links().
--------8<-------------
>
> Or is it caused by the wrong usage?
>
> > > +
> > > link = media_create_ancillary_link(&n->sd->entity, &sd->entity);
> > >
> > > #endif
> >
--
Kind regards,
Sakari Ailus
