sound: Don't assume i2c device probing always succeeds

At Wed, 30 Sep 2009 17:00:06 +0200,
Jean Delvare wrote:
> 
> Hi Takashi,
> 
> Thanks for the swift reply.
> 
> On Wed, 30 Sep 2009 16:13:49 +0200, Takashi Iwai wrote:
> > At Wed, 30 Sep 2009 15:25:42 +0200,
> > Jean Delvare wrote:
> > > 
> > > If i2c device probing fails, then there is no driver to dereference
> > > after calling i2c_new_device(). Stop assuming that probing will always
> > > succeed, to avoid NULL pointer dereferences. We have an easier access
> > > to the driver anyway.
> > > 
> > > Reported-by: Tim Shepard <shep@alum.mit.edu>
> > > Signed-off-by: Jean Delvare <khali@linux-fr.org>
> > > Cc: Johannes Berg <johannes@sipsolutions.net>
> > > ---
> > > The code is similar to the one in therm_adt746x, for which Tim reported
> > > a real-world oops, so it should be fixed ASAP.
> > 
> > Jean, thanks for the patch.
> > 
> > I'm just wondering whether the additional NULL check of client->driver
> > would be enough?  If yes, sound/aoa/onyx.c has it, at least, and we
> > can add the similar checks to the rest, too.
> 
> The NULL check of client->driver, if followed by a call to
> i2c_unregister_device(), would indeed be enough. But unlike the onyx
> driver which we know we sometimes load erroneously, the other drivers
> should never fail. I am reluctant to add code to handle error cases
> which are not supposed to happen, which is why I prefer my proposed
> fix: it does not add code.
> 
> That being said, I will be happy with any solution that fixes the
> problem, so if you prefer client->driver NULL checks, I can send a
> patch doing this.

Yes, indeed I prefer NULL check because the user can know the error
at the right place.  I share your concern about the code addition,
though :)

I already made a patch below, but it's totally untested.
It'd be helpful if someone can do review and build-test it.


thanks,

Takashi

---

On Wed, 30 Sep 2009 17:15:49 +0200, Takashi Iwai wrote:
> Yes, indeed I prefer NULL check because the user can know the error
> at the right place.  I share your concern about the code addition,
> though :)
> 
> I already made a patch below, but it's totally untested.
> It'd be helpful if someone can do review and build-test it.
> 
> 
> thanks,
> 
> Takashi
> 
> ---
> diff --git a/sound/aoa/codecs/tas.c b/sound/aoa/codecs/tas.c
> index f0ebc97..0f810c8 100644
> --- a/sound/aoa/codecs/tas.c
> +++ b/sound/aoa/codecs/tas.c
> @@ -897,6 +897,10 @@ static int tas_create(struct i2c_adapter *adapter,
>  	client = i2c_new_device(adapter, &info);
>  	if (!client)
>  		return -ENODEV;
> +	if (!client->driver) {
> +		i2c_unregister_device(client);
> +		return -ENODEV;
> +	}
>  
>  	/*
>  	 * Let i2c-core delete that device on driver removal.
> diff --git a/sound/ppc/keywest.c b/sound/ppc/keywest.c
> index 835fa19..473c5a6 100644
> --- a/sound/ppc/keywest.c
> +++ b/sound/ppc/keywest.c
> @@ -59,6 +59,13 @@ static int keywest_attach_adapter(struct i2c_adapter *adapter)
>  	strlcpy(info.type, "keywest", I2C_NAME_SIZE);
>  	info.addr = keywest_ctx->addr;
>  	keywest_ctx->client = i2c_new_device(adapter, &info);
> +	if (!keywest_ctx->client)
> +		return -ENODEV;
> +	if (!keywest_ctx->client->driver) {
> +		i2c_unregister_device(keywest_ctx->client);
> +		keywest_ctx->client = NULL;
> +		return -ENODEV;
> +	}
>  	
>  	/*
>  	 * Let i2c-core delete that device on driver removal.

This looks good to me. Please add the following comment before the
client->driver check in both drivers:

	/*
	 * We know the driver is already loaded, so the device should be
	 * already bound. If not it means binding failed, and then there
	 * is no point in keeping the device instantiated.
	 */

Otherwise it's a little difficult to understand why the check is there.

At Wed, 30 Sep 2009 18:55:05 +0200,
Jean Delvare wrote:
> 
> On Wed, 30 Sep 2009 17:15:49 +0200, Takashi Iwai wrote:
> > Yes, indeed I prefer NULL check because the user can know the error
> > at the right place.  I share your concern about the code addition,
> > though :)
> > 
> > I already made a patch below, but it's totally untested.
> > It'd be helpful if someone can do review and build-test it.
> > 
> > 
> > thanks,
> > 
> > Takashi
> > 
> > ---
> > diff --git a/sound/aoa/codecs/tas.c b/sound/aoa/codecs/tas.c
> > index f0ebc97..0f810c8 100644
> > --- a/sound/aoa/codecs/tas.c
> > +++ b/sound/aoa/codecs/tas.c
> > @@ -897,6 +897,10 @@ static int tas_create(struct i2c_adapter *adapter,
> >  	client = i2c_new_device(adapter, &info);
> >  	if (!client)
> >  		return -ENODEV;
> > +	if (!client->driver) {
> > +		i2c_unregister_device(client);
> > +		return -ENODEV;
> > +	}
> >  
> >  	/*
> >  	 * Let i2c-core delete that device on driver removal.
> > diff --git a/sound/ppc/keywest.c b/sound/ppc/keywest.c
> > index 835fa19..473c5a6 100644
> > --- a/sound/ppc/keywest.c
> > +++ b/sound/ppc/keywest.c
> > @@ -59,6 +59,13 @@ static int keywest_attach_adapter(struct i2c_adapter *adapter)
> >  	strlcpy(info.type, "keywest", I2C_NAME_SIZE);
> >  	info.addr = keywest_ctx->addr;
> >  	keywest_ctx->client = i2c_new_device(adapter, &info);
> > +	if (!keywest_ctx->client)
> > +		return -ENODEV;
> > +	if (!keywest_ctx->client->driver) {
> > +		i2c_unregister_device(keywest_ctx->client);
> > +		keywest_ctx->client = NULL;
> > +		return -ENODEV;
> > +	}
> >  	
> >  	/*
> >  	 * Let i2c-core delete that device on driver removal.
> 
> This looks good to me. Please add the following comment before the
> client->driver check in both drivers:
> 
> 	/*
> 	 * We know the driver is already loaded, so the device should be
> 	 * already bound. If not it means binding failed, and then there
> 	 * is no point in keeping the device instantiated.
> 	 */
> 
> Otherwise it's a little difficult to understand why the check is there.

Fair enough.  I applied the patch with the comment now.
Thanks!


Takashi

Hi Takashi,

On Thu, 01 Oct 2009 08:52:59 +0200, Takashi Iwai wrote:
> At Wed, 30 Sep 2009 18:55:05 +0200,
> Jean Delvare wrote:
> > 
> > On Wed, 30 Sep 2009 17:15:49 +0200, Takashi Iwai wrote:
> > > Yes, indeed I prefer NULL check because the user can know the error
> > > at the right place.  I share your concern about the code addition,
> > > though :)
> > > 
> > > I already made a patch below, but it's totally untested.
> > > It'd be helpful if someone can do review and build-test it.
> > > 
> > > 
> > > thanks,
> > > 
> > > Takashi
> > > 
> > > ---
> > > diff --git a/sound/aoa/codecs/tas.c b/sound/aoa/codecs/tas.c
> > > index f0ebc97..0f810c8 100644
> > > --- a/sound/aoa/codecs/tas.c
> > > +++ b/sound/aoa/codecs/tas.c
> > > @@ -897,6 +897,10 @@ static int tas_create(struct i2c_adapter *adapter,
> > >  	client = i2c_new_device(adapter, &info);
> > >  	if (!client)
> > >  		return -ENODEV;
> > > +	if (!client->driver) {
> > > +		i2c_unregister_device(client);
> > > +		return -ENODEV;
> > > +	}
> > >  
> > >  	/*
> > >  	 * Let i2c-core delete that device on driver removal.
> > > diff --git a/sound/ppc/keywest.c b/sound/ppc/keywest.c
> > > index 835fa19..473c5a6 100644
> > > --- a/sound/ppc/keywest.c
> > > +++ b/sound/ppc/keywest.c
> > > @@ -59,6 +59,13 @@ static int keywest_attach_adapter(struct i2c_adapter *adapter)
> > >  	strlcpy(info.type, "keywest", I2C_NAME_SIZE);
> > >  	info.addr = keywest_ctx->addr;
> > >  	keywest_ctx->client = i2c_new_device(adapter, &info);
> > > +	if (!keywest_ctx->client)
> > > +		return -ENODEV;
> > > +	if (!keywest_ctx->client->driver) {
> > > +		i2c_unregister_device(keywest_ctx->client);
> > > +		keywest_ctx->client = NULL;
> > > +		return -ENODEV;
> > > +	}
> > >  	
> > >  	/*
> > >  	 * Let i2c-core delete that device on driver removal.
> > 
> > This looks good to me. Please add the following comment before the
> > client->driver check in both drivers:
> > 
> > 	/*
> > 	 * We know the driver is already loaded, so the device should be
> > 	 * already bound. If not it means binding failed, and then there
> > 	 * is no point in keeping the device instantiated.
> > 	 */
> > 
> > Otherwise it's a little difficult to understand why the check is there.
> 
> Fair enough.  I applied the patch with the comment now.
> Thanks!

I see this is upstream now. While the keywest fix was essentially
theoretical, the tas one addresses a crash which really could happen,
so I think it would be worth sending to stable for 2.6.31. What do you
think? Will you take care, or do you want me to?

Thanks,

At Sun, 4 Oct 2009 11:35:21 +0200,
Jean Delvare wrote:
> 
> Hi Takashi,
> 
> On Thu, 01 Oct 2009 08:52:59 +0200, Takashi Iwai wrote:
> > At Wed, 30 Sep 2009 18:55:05 +0200,
> > Jean Delvare wrote:
> > > 
> > > On Wed, 30 Sep 2009 17:15:49 +0200, Takashi Iwai wrote:
> > > > Yes, indeed I prefer NULL check because the user can know the error
> > > > at the right place.  I share your concern about the code addition,
> > > > though :)
> > > > 
> > > > I already made a patch below, but it's totally untested.
> > > > It'd be helpful if someone can do review and build-test it.
> > > > 
> > > > 
> > > > thanks,
> > > > 
> > > > Takashi
> > > > 
> > > > ---
> > > > diff --git a/sound/aoa/codecs/tas.c b/sound/aoa/codecs/tas.c
> > > > index f0ebc97..0f810c8 100644
> > > > --- a/sound/aoa/codecs/tas.c
> > > > +++ b/sound/aoa/codecs/tas.c
> > > > @@ -897,6 +897,10 @@ static int tas_create(struct i2c_adapter *adapter,
> > > >  	client = i2c_new_device(adapter, &info);
> > > >  	if (!client)
> > > >  		return -ENODEV;
> > > > +	if (!client->driver) {
> > > > +		i2c_unregister_device(client);
> > > > +		return -ENODEV;
> > > > +	}
> > > >  
> > > >  	/*
> > > >  	 * Let i2c-core delete that device on driver removal.
> > > > diff --git a/sound/ppc/keywest.c b/sound/ppc/keywest.c
> > > > index 835fa19..473c5a6 100644
> > > > --- a/sound/ppc/keywest.c
> > > > +++ b/sound/ppc/keywest.c
> > > > @@ -59,6 +59,13 @@ static int keywest_attach_adapter(struct i2c_adapter *adapter)
> > > >  	strlcpy(info.type, "keywest", I2C_NAME_SIZE);
> > > >  	info.addr = keywest_ctx->addr;
> > > >  	keywest_ctx->client = i2c_new_device(adapter, &info);
> > > > +	if (!keywest_ctx->client)
> > > > +		return -ENODEV;
> > > > +	if (!keywest_ctx->client->driver) {
> > > > +		i2c_unregister_device(keywest_ctx->client);
> > > > +		keywest_ctx->client = NULL;
> > > > +		return -ENODEV;
> > > > +	}
> > > >  	
> > > >  	/*
> > > >  	 * Let i2c-core delete that device on driver removal.
> > > 
> > > This looks good to me. Please add the following comment before the
> > > client->driver check in both drivers:
> > > 
> > > 	/*
> > > 	 * We know the driver is already loaded, so the device should be
> > > 	 * already bound. If not it means binding failed, and then there
> > > 	 * is no point in keeping the device instantiated.
> > > 	 */
> > > 
> > > Otherwise it's a little difficult to understand why the check is there.
> > 
> > Fair enough.  I applied the patch with the comment now.
> > Thanks!
> 
> I see this is upstream now. While the keywest fix was essentially
> theoretical, the tas one addresses a crash which really could happen,
> so I think it would be worth sending to stable for 2.6.31. What do you
> think? Will you take care, or do you want me to?

Agreed, it's safer to send the patch to stable tree.
I'm going to submit it.


thanks,

Takashi