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

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Date:   Fri, 30 Apr 2021 11:34:50 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>
Cc:     Colin King <colin.king@...onical.com>,
        Ryder Lee <ryder.lee@...iatek.com>,
        Jianjun Wang <jianjun.wang@...iatek.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH][next] PCI: mediatek-gen3: Add missing null pointer check

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@...onical.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@...onical.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