linux-kernel - Re: [Xen-devel] [PATCH] block: xen-blkfront: Fix possible NULL ptr dereference

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Date:	Mon, 11 Nov 2013 10:48:00 +0100
From:	Roger Pau Monné <roger.pau@...rix.com>
To:	Felipe Pena <felipensp@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH] block: xen-blkfront: Fix possible NULL ptr
 dereference

On 09/11/13 16:36, Felipe Pena wrote:
> In the blkif_release function the bdget_disk() call might returns
> a NULL ptr which might be dereferenced on bdev->bd_openers checking
> 
> Signed-off-by: Felipe Pena <felipensp@...il.com>
> ---
>  drivers/block/xen-blkfront.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index a4660bb..7bb1552 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -1959,6 +1959,9 @@ static void blkif_release(struct gendisk *disk, fmode_t mode)
>  
>  	bdev = bdget_disk(disk, 0);
>  
> +	if (!bdev)
> +		goto out_mutex;

Is this actually possible? By looking at blkfront code, it seems like we
don't remove the device if it is still open, so maybe this should be a
BUG_ON instead of failing silently.

Roger.
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