linux-kernel - Re: [PATCH v2] ASoC: fsl_easrc: Check for null pointer before dereferencing "ctx" in fsl_easrc_hw

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Date:   Sat, 25 Apr 2020 15:49:16 +0800
From:   Shengjiu Wang <shengjiu.wang@...il.com>
To:     Shengjiu Wang <shengjiu.wang@....com>
Cc:     Timur Tabi <timur@...nel.org>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Liam Girdwood <lgirdwood@...il.com>, perex@...ex.cz,
        Takashi Iwai <tiwai@...e.com>, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] ASoC: fsl_easrc: Check for null pointer before
 dereferencing "ctx" in fsl_easrc_hw_free()

On Sat, Apr 25, 2020 at 3:30 PM Shengjiu Wang <shengjiu.wang@....com> wrote:
>
> The patch 955ac624058f: "ASoC: fsl_easrc: Add EASRC ASoC CPU DAI
> drivers" from Apr 16, 2020, leads to the following Smatch complaint:
>
> sound/soc/fsl/fsl_easrc.c:1529 fsl_easrc_hw_free()
> warn: variable dereferenced before check 'ctx' (see line 1527)
>
> sound/soc/fsl/fsl_easrc.c
>   1526          struct fsl_asrc_pair *ctx = runtime->private_data;
>   1527          struct fsl_easrc_ctx_priv *ctx_priv = ctx->private;
>                                                       ^^^^^
> Dereference
>
>   1528
>   1529          if (ctx && (ctx_priv->ctx_streams & BIT(substream->stream))) {
>                     ^^^
> This check is too late, to prevent a NULL dereference.
>
>   1530                  ctx_priv->ctx_streams &= ~BIT(substream->stream);
>   1531                  fsl_easrc_release_context(ctx);
>
> Fixes: 955ac624058f ("ASoC: fsl_easrc: Add EASRC ASoC CPU DAI drivers")
> Reported-by: Dan Carpenter <dan.carpenter@...cle.com>
> Signed-off-by: Shengjiu Wang <shengjiu.wang@....com>
> ---

Sorry，I forgot the changes:
changes in v2:
- refine the commit subject.

best regards
Wang shengjiu

>  sound/soc/fsl/fsl_easrc.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/sound/soc/fsl/fsl_easrc.c b/sound/soc/fsl/fsl_easrc.c
> index 97658e1f4989..20326bffab64 100644
> --- a/sound/soc/fsl/fsl_easrc.c
> +++ b/sound/soc/fsl/fsl_easrc.c
> @@ -1524,9 +1524,14 @@ static int fsl_easrc_hw_free(struct snd_pcm_substream *substream,
>  {
>         struct snd_pcm_runtime *runtime = substream->runtime;
>         struct fsl_asrc_pair *ctx = runtime->private_data;
> -       struct fsl_easrc_ctx_priv *ctx_priv = ctx->private;
> +       struct fsl_easrc_ctx_priv *ctx_priv;
>
> -       if (ctx && (ctx_priv->ctx_streams & BIT(substream->stream))) {
> +       if (!ctx)
> +               return -EINVAL;
> +
> +       ctx_priv = ctx->private;
> +
> +       if (ctx_priv->ctx_streams & BIT(substream->stream)) {
>                 ctx_priv->ctx_streams &= ~BIT(substream->stream);
>                 fsl_easrc_release_context(ctx);
>         }
> --
> 2.21.0
>