linux-kernel - Re: [PATCH v2] block: Fix use-after-free in blkdev

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Message-ID: <20200605180845.GU30374@kadam>
Date:   Fri, 5 Jun 2020 21:08:45 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Jason Yan <yanaijie@...wei.com>,
        Markus Elfring <Markus.Elfring@....de>,
        linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        hulkci@...wei.com, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH v2] block: Fix use-after-free in blkdev_get()

On Fri, Jun 05, 2020 at 04:42:36PM +0200, Jan Kara wrote:
> On Fri 05-06-20 12:43:54, Dan Carpenter wrote:
> > I wonder if maybe the best fix is to re-add the "if (!res) " check back
> > to blkdev_get().
> 
> Well, it won't be that simple since we need to call bd_abort_claiming()
> under bdev->bd_mutex. And the fact that __blkdev_get() frees the reference
> you pass to it is somewhat subtle and surprising so I think we are better
> off getting rid of that.

Fair enough.

Jason Yan sent a v3 of this patch that frees "whole".  I've looked it
over pretty close and I think it's probably correct.

(not that my opinion should count for much because I don't know this
code very well at all).

regards,
dan carpenter