xhci: tegra: Prevent error pointer dereference

[Thierry Reding <thierry.reding@gmail.com>]

On Wed, Feb 20, 2019 at 05:16:12PM +0100, Greg Kroah-Hartman wrote:
> On Wed, Feb 20, 2019 at 02:48:41PM +0100, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > During initialization, the host and super-speed power domains will
> > contain an ERR_PTR() encoded error code rather than being NULL. To
> > avoid a crash, use a !IS_ERR_OR_NULL() condition during cleanup.
> > 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> >  drivers/usb/host/xhci-tegra.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/usb/host/xhci-tegra.c b/drivers/usb/host/xhci-tegra.c
> > index 938ff06c0349..efb0cad8710e 100644
> > --- a/drivers/usb/host/xhci-tegra.c
> > +++ b/drivers/usb/host/xhci-tegra.c
> > @@ -941,9 +941,9 @@ static void tegra_xusb_powerdomain_remove(struct device *dev,
> >  		device_link_del(tegra->genpd_dl_ss);
> >  	if (tegra->genpd_dl_host)
> >  		device_link_del(tegra->genpd_dl_host);
> > -	if (tegra->genpd_dev_ss)
> > +	if (!IS_ERR_OR_NULL(tegra->genpd_dev_ss))
> >  		dev_pm_domain_detach(tegra->genpd_dev_ss, true);
> > -	if (tegra->genpd_dev_host)
> > +	if (!IS_ERR_OR_NULL(tegra->genpd_dev_host))
> >  		dev_pm_domain_detach(tegra->genpd_dev_host, true);
> >  }
> 
> Should this go to older kernels?  If so, any hint as to what commit this
> "fixes:"?

Technically this:

Fixes: 6494a9ad86de ("usb: xhci: tegra: Add genpd support")

which was merged into v4.20.

However, I have never seen this actually crash on current kernels and
only came across it while working on a change to reset controls which
can cause dev_pm_domain_attach_by_name() to fail. That function can't
fail in current kernels, so I don't think we need to fix this in old
kernels. So if we can get this into v5.0, that'd be good enough for
me.

Thierry