linux-kernel - Re: [PATCH] use after free bug in __blkdev

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Message-ID: <20091026072607.GZ10727@kernel.dk>
Date:	Mon, 26 Oct 2009 08:26:07 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Neil Brown <neilb@...e.de>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] use after free bug in __blkdev_get

On Mon, Oct 26 2009, Neil Brown wrote:
> 
> 
> commit 0762b8bde9729f10f8e6249809660ff2ec3ad735
> (from 14 months ago) introduced a use-after-free bug which has just
> recently started manifesting in my md testing.
> I tried git bisect to find out what caused the bug to start
> manifesting, and it could have been the recent change to
> blk_unregister_queue (48c0d4d4c04) but the results were inconclusive.
> 
> This patch certainly fixes my symptoms and looks correct as the two
> calls are now in the same order as elsewhere in that function.
> 
> Signed-off-by: NeilBrown <neilb@...e.de>
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 9cf4b92..8bed055 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -1248,8 +1248,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
>  			bd_set_size(bdev, (loff_t)bdev->bd_part->nr_sects << 9);
>  		}
>  	} else {
> -		put_disk(disk);
>  		module_put(disk->fops->owner);
> +		put_disk(disk);
>  		disk = NULL;
>  		if (bdev->bd_contains == bdev) {
>  			if (bdev->bd_disk->fops->open) {

Thanks Neil, good catch! Applied.

-- 
Jens Axboe

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