linux-kernel - Re: [Xen-devel] [PATCH 7/9] xen/xenbus: Check before dereferencing it.

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Message-ID: <1317369681.26672.218.camel@zakaz.uk.xensource.com>
Date:	Fri, 30 Sep 2011 09:01:21 +0100
From:	Ian Campbell <Ian.Campbell@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Dan Carpenter <error27@...il.com>
Subject: Re: [Xen-devel] [PATCH 7/9] xen/xenbus: Check before dereferencing
 it.

On Thu, 2011-09-29 at 20:52 +0100, Konrad Rzeszutek Wilk wrote:
> . we do the check whether 'xdev' is NULL - but after we have
> dereferenced it.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  drivers/xen/xenbus/xenbus_probe_backend.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
> index 60adf91..331589a 100644
> --- a/drivers/xen/xenbus/xenbus_probe_backend.c
> +++ b/drivers/xen/xenbus/xenbus_probe_backend.c
> @@ -103,10 +103,11 @@ static int xenbus_uevent_backend(struct device *dev,
>  		return -ENODEV;
>  
>  	xdev = to_xenbus_device(dev);

to_xenbus_device is just container_of. The only way it would return NULL
is if dev == offsetof(struct xenbus_device, dev), which isn't terribly
likely. A more likely error would be dev == NULL and we just checked
above.

> -	bus = container_of(xdev->dev.bus, struct xen_bus_type, bus);
>  	if (xdev == NULL)
>  		return -ENODEV;
>  
> +	bus = container_of(xdev->dev.bus, struct xen_bus_type, bus);
> +
>  	if (add_uevent_var(env, "MODALIAS=xen-backend:%s", xdev->devicetype))
>  		return -ENOMEM;
>  


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