Re: [PATCH -next] PCI: dra7xx: Fix potential NULL dereference

From: Bjorn Helgaas <helgaas@kernel.org>
To: Wei Yongjun <weiyongjun1@huawei.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	linux-omap@vger.kernel.org, linux-pci@vger.kernel.org,
	kernel-janitors@vger.kernel.org
Subject: Re: [PATCH -next] PCI: dra7xx: Fix potential NULL dereference
Date: Thu, 18 Jan 2018 14:42:24 +0000	[thread overview]
Message-ID: <20180118144224.GF53542@bhelgaas-glaptop.roam.corp.google.com> (raw)
In-Reply-To: <1516284037-81537-1-git-send-email-weiyongjun1@huawei.com>

On Thu, Jan 18, 2018 at 02:00:37PM +0000, Wei Yongjun wrote:
> platform_get_resource_byname() may fail and return NULL, so we should
> better check it's return value to avoid a NULL pointer dereference a
> bit later in the code.
> 
> This is detected by Coccinelle semantic patch.
> 
> @@
> expression pdev, res, n, t, e, e1, e2;
> @@
> 
> res = platform_get_resource_byname(pdev, t, n);
> + if (!res)
> +   return -EINVAL;
> ... when != res = NULL
> e = devm_ioremap(e1, res->start, e2);

This pattern of:

  platform_get_resource_byname
  devm_ioremap

is extremely common and could perhaps be factored out.  There are
already a few private versions, e.g., request_and_map(),
msm_ioremap(), ssi_get_iomem().

request_and_map() also includes devm_request_mem_region(), which
probably *should* be included but usually seems to be omitted.

> Fixes: 608793e27b33 ("PCI: dwc: dra7xx: Add EP mode support")
> Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
> ---
>  drivers/pci/dwc/pci-dra7xx.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/pci/dwc/pci-dra7xx.c b/drivers/pci/dwc/pci-dra7xx.c
> index 8bf7c27..aafded8 100644
> --- a/drivers/pci/dwc/pci-dra7xx.c
> +++ b/drivers/pci/dwc/pci-dra7xx.c
> @@ -409,11 +409,15 @@ static int __init dra7xx_add_pcie_ep(struct dra7xx_pcie *dra7xx,
>  	ep->ops = &pcie_ep_ops;
>  
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "ep_dbics");
> +	if (!res)
> +		return -EINVAL;
>  	pci->dbi_base = devm_ioremap(dev, res->start, resource_size(res));
>  	if (!pci->dbi_base)
>  		return -ENOMEM;
>  
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "ep_dbics2");
> +	if (!res)
> +		return -EINVAL;
>  	pci->dbi_base2 = devm_ioremap(dev, res->start, resource_size(res));
>  	if (!pci->dbi_base2)
>  		return -ENOMEM;
> @@ -462,6 +466,8 @@ static int __init dra7xx_add_pcie_port(struct dra7xx_pcie *dra7xx,
>  		return ret;
>  
>  	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "rc_dbics");
> +	if (!res)
> +		return -EINVAL;
>  	pci->dbi_base = devm_ioremap(dev, res->start, resource_size(res));
>  	if (!pci->dbi_base)
>  		return -ENOMEM;
> 