linux-kernel - Re: [PATCH] xen/pciback: Prevent NULL pointer dereference in quirks

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Date:   Fri, 6 Dec 2019 10:11:09 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Stefan Nuernberger <snu@...zon.com>, linux-kernel@...r.kernel.org
Cc:     Juergen Gross <jgross@...e.com>,
        Ross Lagerwall <ross.lagerwall@...rix.com>,
        Uwe Dannowski <uwed@...zon.de>,
        Conny Seidel <consei@...zon.de>,
        xen-devel@...ts.xenproject.org, stable@...r.kernel.org
Subject: Re: [PATCH] xen/pciback: Prevent NULL pointer dereference in
 quirks_show

On 12/6/19 8:48 AM, Stefan Nuernberger wrote:
> From: Uwe Dannowski <uwed@...zon.de>
>
> Reading /sys/bus/pci/drivers/pciback/quirks while unbinding can result
> in dereferencing a NULL pointer. Instead, skip printing information
> about the dangling quirk.
>
> Reported-by: Conny Seidel <consei@...zon.de>
> Signed-off-by: Uwe Dannowski <uwed@...zon.de>
> Signed-off-by: Stefan Nuernberger <snu@...zon.com>
>
> Cc: xen-devel@...ts.xenproject.org
> Cc: stable@...r.kernel.org
> ---
>  drivers/xen/xen-pciback/pci_stub.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/xen/xen-pciback/pci_stub.c b/drivers/xen/xen-pciback/pci_stub.c
> index 097410a7cdb7..da725e474294 100644
> --- a/drivers/xen/xen-pciback/pci_stub.c
> +++ b/drivers/xen/xen-pciback/pci_stub.c
> @@ -1346,6 +1346,8 @@ static ssize_t quirks_show(struct device_driver *drv, char *buf)
>  				   quirk->devid.subdevice);
>  
>  		dev_data = pci_get_drvdata(quirk->pdev);
> +		if (!dev_data)
> +			continue;
>  
>  		list_for_each_entry(cfg_entry, &dev_data->config_fields, list) {

Couldn't you have the same race here?

-boris

>  			field = cfg_entry->field;