Re: [PATCH] I2c: busses - Fix possible NULL derefrence.

From: Thierry Reding
Date: Mon Jan 30 2017 - 03:55:10 EST

On Mon, Jan 30, 2017 at 09:07:15AM +0100, Uwe Kleine-KÃnig wrote:
> Hello,
> On Mon, Jan 30, 2017 at 08:12:17AM +0100, Thierry Reding wrote:
> > On Mon, Jan 30, 2017 at 10:33:07AM +0530, Shailendra Verma wrote:
> > > of_device_get_match_data could return NULL, and so can cause
> > > a NULL pointer dereference later.
> > >
> > > Signed-off-by: Shailendra Verma <shailendra.v@xxxxxxxxxxx>
> > > ---
> > > drivers/i2c/busses/i2c-tegra.c | 4 ++++
> > > 1 file changed, 4 insertions(+)
> >
> > This will never happen. Any match in the OF table that would cause the
> > ->probe() to occur has a valid .data pointer associated with it.
> Theoretically you could (I think) bind that driver to a node with
> compatible = "tegra-i2c";

That's not a valid compatible string and I don't think this could end up
anywhere that would make the driver bind. Even if it did I think it'd be
good to crash rather than error out to make it very obvious that you've
made a mistake that needs to be immediately fixed.

If you error out it's much more likely that people won't notice.

> Anyhow, even if today there was no possibility this could happen, that's
> something that might easily be changed by a future change. So I doubt
> "this will never happen" stays true for sure and being defensive is a
> good idea.

Let's revisit this again *if* this ever becomes a real issue. There's no
use in adding dead code to the kernel to handle hypothetical use-cases.

> And even a BUG would be better than a silent NULL pointer dereference.

I've never encountered a NULL pointer dereference that was silent. =)


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