linux-kernel - Re: [PATCH 1/4] crypto: s5p-sss: Fix race in error handling

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Date:   Mon, 17 Sep 2018 14:59:52 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     c.manszewski@...sung.com
Cc:     linux-crypto@...r.kernel.org, vz@...ia.com,
        k.konieczny@...tner.samsung.com, herbert@...dor.apana.org.au,
        davem@...emloft.net,
        "linux-samsung-soc@...r.kernel.org" 
        <linux-samsung-soc@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] crypto: s5p-sss: Fix race in error handling

On Thu, 13 Sep 2018 at 09:59, Christoph Manszewski
<c.manszewski@...sung.com> wrote:
>
> Remove a race condition introduced by error path in functions:
> s5p_aes_interrupt and s5p_aes_crypt_start. Setting the busy field of
> struct s5p_aes_dev to false made it possible for s5p_tasklet_cb to
> change the req field, before s5p_aes_complete was called.

Nice catch. Indeed the code looks racy.

>
> Change the first parameter of s5p_aes_complete to struct
> ablkcipher_request. Before spin_unlock, make a copy of the currently
> handled request, to ensure s5p_aes_complete function call with the
> correct request.
>
> Signed-off-by: Christoph Manszewski <c.manszewski@...sung.com>
> ---
>  drivers/crypto/s5p-sss.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/crypto/s5p-sss.c b/drivers/crypto/s5p-sss.c
> index faa282074e5a..0cf3f12d8f74 100644
> --- a/drivers/crypto/s5p-sss.c
> +++ b/drivers/crypto/s5p-sss.c
> @@ -475,9 +475,9 @@ static void s5p_sg_done(struct s5p_aes_dev *dev)
>  }
>
>  /* Calls the completion. Cannot be called with dev->lock hold. */
> -static void s5p_aes_complete(struct s5p_aes_dev *dev, int err)
> +static void s5p_aes_complete(struct ablkcipher_request *req, int err)
>  {
> -       dev->req->base.complete(&dev->req->base, err);
> +       req->base.complete(&req->base, err);
>  }
>
>  static void s5p_unset_outdata(struct s5p_aes_dev *dev)
> @@ -655,6 +655,7 @@ static irqreturn_t s5p_aes_interrupt(int irq, void *dev_id)
>  {
>         struct platform_device *pdev = dev_id;
>         struct s5p_aes_dev *dev = platform_get_drvdata(pdev);
> +       struct ablkcipher_request *req;
>         int err_dma_tx = 0;
>         int err_dma_rx = 0;
>         int err_dma_hx = 0;
> @@ -725,9 +726,10 @@ static irqreturn_t s5p_aes_interrupt(int irq, void *dev_id)
>                 if (err_dma_hx == 1)
>                         s5p_set_dma_hashdata(dev, dev->hash_sg_iter);
>
> +               req = dev->req;

In this path it should not be needed, so just
s5p_aes_complete(dev->req)? At this point dev->busy is true so
s5p_aes_handle_req() will exit before starting new tasklet. Also the
interrupt is an effect of finishing work by device scheduled in last
tasklet... so obviously no tasklet should be running.

>                 spin_unlock_irqrestore(&dev->lock, flags);
>
> -               s5p_aes_complete(dev, 0);
> +               s5p_aes_complete(req, 0);
>                 /* Device is still busy */
>                 tasklet_schedule(&dev->tasklet);
>         } else {
> @@ -755,8 +757,9 @@ static irqreturn_t s5p_aes_interrupt(int irq, void *dev_id)
>         if (err_dma_hx == 1)
>                 s5p_set_dma_hashdata(dev, dev->hash_sg_iter);
>
> +       req = dev->req;

Please put it before new line (so there will be new line before
unlock). Logically it should not be separated from other commands in
error path.

Best regards,
Krzysztof