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Date: Thu, 25 Aug 2016 09:38:26 +0200
From: Christoph Hellwig <hch@lst.de>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Jens Axboe <axboe@fb.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        linux-fsdevel@vger.kernel.org,
        Maxim Patlasov <mpatlasov@virtuozzo.com>,
        Christoph Hellwig <hch@lst.de>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs/block_dev: fix potential NULL ptr deref in
        freeze_bdev()
Message-ID: <20160825073826.GB18622@lst.de>
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On Tue, Aug 23, 2016 at 06:55:31PM +0300, Andrey Ryabinin wrote:
> Calling freeze_bdev() twice on the same block device without mounted
> filesystem get_super() will return NULL, which will lead to NULL-ptr
> dereference later in drop_super().
> 
> Check get_super() result to fix that.
> 
> Note, that this is a purely theoretical issue. We have only 3
> freeze_bdev() callers. 2 of them are in filesystem code and used on a
> device with mounted fs. The third one in lock_fs() has protection in
> upper-layer code against freezing block device the second time without
> thawing it first.
> 
> Signed-off-by: Andrey Ryabinin <aryabinin@virtuozzo.com>

Looks fine,

Reviewed-by: Christoph Hellwig <hch@lst.de>