linux-kernel - Re: [PATCH -next] bcache: Fix potential NULL pointer dereference

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Message-ID: <20190130105817.GA12598@kmo-pixel>
Date:   Wed, 30 Jan 2019 05:58:17 -0500
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     YueHaibing <yuehaibing@...wei.com>
Cc:     colyli@...e.de, linux-kernel@...r.kernel.org,
        linux-bcache@...r.kernel.org
Subject: Re: [PATCH -next] bcache: Fix potential NULL pointer dereference

On Wed, Jan 30, 2019 at 06:21:12PM +0800, YueHaibing wrote:
> There is a potential NULL pointer dereference in case
> kzalloc() fails and returns NULL.
> 
> Fixes: bc082a55d25c ("bcache: fix inaccurate io state for detached bcache devices")
> Signed-off-by: YueHaibing <yuehaibing@...wei.com>
> ---
>  drivers/md/bcache/request.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 1507041..a50afa4 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -1094,6 +1094,8 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio)
>  	 * which would call closure_get(&dc->disk.cl)
>  	 */
>  	ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
> +	if (!ddip)
> +		return;
>  	ddip->d = d;
>  	ddip->start_time = jiffies;
>  	ddip->bi_end_io = bio->bi_end_io;

This should be using a mempool/bioset... just returning from a make_request
function is not correct, that's a serious bug - you're just dropping an IO on
the floor, which is going to cause whatever submitted that IO to hang.