linux-kernel - Re: [GIT PULL] block fixes for 2.6.32-rc

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Date:	Wed, 28 Oct 2009 12:00:08 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Jens Axboe <jens.axboe@...cle.com>
cc:	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] block fixes for 2.6.32-rc



On Wed, 28 Oct 2009, Jens Axboe wrote:
> 
> Neil Brown (1):
>       block: use after free bug in __blkdev_get
>
> 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) {

Is this really right? You do the module-put while the disk is still 
available..

I get the feeling that it might have been better to do

	struct module *mod = disk->fops->owner;
	put_disk(disk);
	module_put(mod);

instead, which tries to make sure that the module is put only after we've 
gotten rid of the disk entirely.

But I dunno. Maybe there is some reason why it's safe either way. You're 
sure the kobject_put() in put_disk will never call to the module?

		Linus
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