Re: [PATCH] memory: brcmstb_dpfe: fix array index out of bounds

[Krzysztof Kozlowski]

On Thu, Aug 20, 2020 at 06:03:33PM -0700, Markus Mayer wrote:
> We would overrun the error_text array if we hit a TIMEOUT condition,
> because we were using the error code "ETIMEDOUT" (which is 110) as an
> array index.
> 
> We fix the problem by correcting the array index and by providing a
> function to retrieve error messages rather than accessing the array
> directly. The function includes a bounds check that prevents the array
> from being overrun.
> 
> Signed-off-by: Markus Mayer <mmayer@xxxxxxxxxxxx>
> ---
> 
> This patch was prepared in response to https://lkml.org/lkml/2020/8/18/505.
> 
>  drivers/memory/brcmstb_dpfe.c | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
> index 81abc4a98a27..a986a849f58e 100644
> --- a/drivers/memory/brcmstb_dpfe.c
> +++ b/drivers/memory/brcmstb_dpfe.c
> @@ -190,11 +190,6 @@ struct brcmstb_dpfe_priv {
>  	struct mutex lock;
>  };
>  
> -static const char * const error_text[] = {
> -	"Success", "Header code incorrect", "Unknown command or argument",
> -	"Incorrect checksum", "Malformed command", "Timed out",
> -};
> -
>  /*
>   * Forward declaration of our sysfs attribute functions, so we can declare the
>   * attribute data structures early.
> @@ -307,6 +302,20 @@ static const struct dpfe_api dpfe_api_v3 = {
>  	},
>  };
>  
> +static const char * const get_error_text(unsigned int i)

The pointer itself is returned by value and you cannot return a const
value. I mean, you can but it does not have an effect. Only pointed
memory should be const (const const char*).

Best regards,
Krzysztof


> +{
> +	static const char * const error_text[] = {
> +		"Success", "Header code incorrect",
> +		"Unknown command or argument", "Incorrect checksum",
> +		"Malformed command", "Timed out", "Unknown error",
> +	};
> +
> +	if (unlikely(i >= ARRAY_SIZE(error_text)))
> +		i = ARRAY_SIZE(error_text) - 1;
> +
> +	return error_text[i];
> +}
> +
>  static bool is_dcpu_enabled(struct brcmstb_dpfe_priv *priv)
>  {
>  	u32 val;
> @@ -446,7 +455,7 @@ static int __send_command(struct brcmstb_dpfe_priv *priv, unsigned int cmd,
>  	}
>  	if (resp != 0) {
>  		mutex_unlock(&priv->lock);
> -		return -ETIMEDOUT;
> +		return -ffs(DCPU_RET_ERR_TIMEDOUT);
>  	}
>  
>  	/* Compute checksum over the message */
> @@ -695,7 +704,7 @@ static ssize_t generic_show(unsigned int command, u32 response[],
>  
>  	ret = __send_command(priv, command, response);
>  	if (ret < 0)
> -		return sprintf(buf, "ERROR: %s\n", error_text[-ret]);
> +		return sprintf(buf, "ERROR: %s\n", get_error_text(-ret));
>  
>  	return 0;
>  }
> -- 
> 2.17.1
>