linux-kernel - Re: [PATCH] Fix NULL pointer dereference in bl_free

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Date:	Tue, 19 Jul 2016 11:21:08 -0400
From:	Anna Schumaker <Anna.Schumaker@...app.com>
To:	Artem Savkov <asavkov@...hat.com>, <linux-nfs@...r.kernel.org>
CC:	<linux-kernel@...r.kernel.org>, <trond.myklebust@...marydata.com>,
	<hch@....de>
Subject: Re: [PATCH] Fix NULL pointer dereference in bl_free_device().

Hi Artem,

On 07/19/2016 07:30 AM, Artem Savkov wrote:
> When bl_parse_deviceid() fails in bl_alloc_deviceid_node() on
> blkdev_get_by_*() step we get an pnfs_block_dev struct that is
> uninitialized except for bdev field which is set to whatever error
> blkdev_get_by_*() returns.  bl_free_device() then tries to call
> blkdev_put() if bdev is not 0 resulting in a wrong pointer dereference.
> 
> Fixing this by making sure bdev is not an error code in bl_free_device().
> 
> Signed-off-by: Artem Savkov <asavkov@...hat.com>
> ---
>  fs/nfs/blocklayout/dev.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/nfs/blocklayout/dev.c b/fs/nfs/blocklayout/dev.c
> index 118252f..7db3af0 100644
> --- a/fs/nfs/blocklayout/dev.c
> +++ b/fs/nfs/blocklayout/dev.c
> @@ -33,7 +33,7 @@ bl_free_device(struct pnfs_block_dev *dev)
>  				pr_err("failed to unregister PR key.\n");
>  		}
>  
> -		if (dev->bdev)
> +		if (dev->bdev && !IS_ERR(dev->bdev))

This looks pretty straightforward, but can you use IS_ERR_OR_NULL() instead?  It accomplishes the same check with slightly cleaner code :)

Thanks,
Anna

>  			blkdev_put(dev->bdev, FMODE_READ | FMODE_WRITE);
>  	}
>  }
>