Re: [PATCH][next] PCI: mediatek-gen3: Add missing null pointer check

Bjorn Helgaas
2021-04-30T16:35:22Z

On Fri, Apr 30, 2021 at 09:47:06AM +0200, Christophe JAILLET wrote:
> Le 29/04/2021 à 13:00, Colin King a écrit :
> > From: Colin Ian King <colin.king@canonical.com>
> >
> > The call to platform_get_resource_byname can potentially return null, so
> > add a null pointer check to avoid a null pointer dereference issue.
> >
> > Addresses-Coverity: ("Dereference null return")
> > Fixes: 441903d9e8f0 ("PCI: mediatek-gen3: Add MediaTek Gen3 driver for MT8192")
> > Signed-off-by: Colin Ian King <colin.king@canonical.com>
> > ---
> > drivers/pci/controller/pcie-mediatek-gen3.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/pci/controller/pcie-mediatek-gen3.c b/drivers/pci/controller/pcie-mediatek-gen3.c
> > index 20165e4a75b2..3c5b97716d40 100644
> > --- a/drivers/pci/controller/pcie-mediatek-gen3.c
> > +++ b/drivers/pci/controller/pcie-mediatek-gen3.c
> > @@ -721,6 +721,8 @@ static int mtk_pcie_parse_port(struct mtk_pcie_port *port)
> > int ret;
> > regs = platform_get_resource_byname(pdev, IORESOURCE_MEM, "pcie-mac");
> > + if (!regs)
> > + return -EINVAL;
> > port->base = devm_ioremap_resource(dev, regs);
> > if (IS_ERR(port->base)) {
> > dev_err(dev, "failed to map register base\n");
> >
>
> Nitpick:
> Using 'devm_platform_ioremap_resource_byname' is slightly less verbose
> and should please Coverity.

Not a nitpick at all. Jianjun is correct that devm_ioremap_resource()
does check "regs" for NULL and it fails gracefully before trying to
dereference it, so the extra check shouldn't be needed. And most
cases in drivers/pci/ look like this, without the extra check:

res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "app");
base = devm_ioremap_resource(dev, res);
if (IS_ERR(base))
...

If devm_platform_ioremap_resource_byname() keeps Coverity happy, I
think that's what we should be doing across drivers/pci/. Coverity
false positives are a hassle.

Seems like something for next cycle since we're in the middle of the
merge window.

> Also, which git repo are you using? On linux-next ([1)], your proposed patch
> is already part of "PCI: mediatek-gen3: Add MediaTek Gen3 driver for
> MT8192".
>
> [1]: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/drivers/pci/controller/pcie-mediatek-gen3.c

I think this is because Lorenzo already squashed Colin's change in.

Bjorn