linux-kernel - Re: [PATCH] scsi: ufs: ufshcd: Remove VLA usage

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Date:   Wed, 16 May 2018 13:54:50 -0700
From:   Subhash Jadavani <subhashj@...eaurora.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        Vinayak Holikatti <vinholikatti@...il.com>,
        "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi-owner@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: ufshcd: Remove VLA usage

On 2018-05-02 16:58, Kees Cook wrote:
> On the quest to remove all VLAs from the kernel[1] this moves buffers
> off the stack. In the second instance, this collapses two separately
> allocated buffers into a single buffer, since they are used 
> consecutively,
> which saves 256 bytes (QUERY_DESC_MAX_SIZE + 1) of stack space.
> 
> [1]
> https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 34 ++++++++++++++++++++++++++--------
>  1 file changed, 26 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 00e79057f870..a271534362f6 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -5958,14 +5958,18 @@ static void ufshcd_init_icc_levels(struct 
> ufs_hba *hba)
>  {
>  	int ret;
>  	int buff_len = hba->desc_size.pwr_desc;
> -	u8 desc_buf[hba->desc_size.pwr_desc];
> +	u8 *desc_buf;
> +
> +	desc_buf = kmalloc(buff_len, GFP_KERNEL);
> +	if (!desc_buf)
> +		return;
> 
>  	ret = ufshcd_read_power_desc(hba, desc_buf, buff_len);
>  	if (ret) {
>  		dev_err(hba->dev,
>  			"%s: Failed reading power descriptor.len = %d ret = %d",
>  			__func__, buff_len, ret);
> -		return;
> +		goto out;
>  	}
> 
>  	hba->init_prefetch_data.icc_level =
> @@ -5983,6 +5987,8 @@ static void ufshcd_init_icc_levels(struct ufs_hba 
> *hba)
>  			"%s: Failed configuring bActiveICCLevel = %d ret = %d",
>  			__func__, hba->init_prefetch_data.icc_level , ret);
> 
> +out:
> +	kfree(desc_buf);
>  }
> 
>  /**
> @@ -6052,9 +6058,17 @@ static int ufs_get_device_desc(struct ufs_hba 
> *hba,
>  			       struct ufs_dev_desc *dev_desc)
>  {
>  	int err;
> +	size_t buff_len;
>  	u8 model_index;
> -	u8 str_desc_buf[QUERY_DESC_MAX_SIZE + 1] = {0};
> -	u8 desc_buf[hba->desc_size.dev_desc];
> +	u8 *desc_buf;
> +
> +	buff_len = max_t(size_t, hba->desc_size.dev_desc,
> +			 QUERY_DESC_MAX_SIZE + 1);
> +	desc_buf = kmalloc(buff_len, GFP_KERNEL);
> +	if (!desc_buf) {
> +		err = -ENOMEM;
> +		goto out;
> +	}
> 
>  	err = ufshcd_read_device_desc(hba, desc_buf, 
> hba->desc_size.dev_desc);
>  	if (err) {
> @@ -6072,7 +6086,10 @@ static int ufs_get_device_desc(struct ufs_hba 
> *hba,
> 
>  	model_index = desc_buf[DEVICE_DESC_PARAM_PRDCT_NAME];
> 
> -	err = ufshcd_read_string_desc(hba, model_index, str_desc_buf,
> +	/* Zero-pad entire buffer for string termination. */
> +	memset(desc_buf, 0, buff_len);
> +
> +	err = ufshcd_read_string_desc(hba, model_index, desc_buf,
>  				      QUERY_DESC_MAX_SIZE, true/*ASCII*/);
>  	if (err) {
>  		dev_err(hba->dev, "%s: Failed reading Product Name. err = %d\n",
> @@ -6080,15 +6097,16 @@ static int ufs_get_device_desc(struct ufs_hba 
> *hba,
>  		goto out;
>  	}
> 
> -	str_desc_buf[QUERY_DESC_MAX_SIZE] = '\0';
> -	strlcpy(dev_desc->model, (str_desc_buf + QUERY_DESC_HDR_SIZE),
> -		min_t(u8, str_desc_buf[QUERY_DESC_LENGTH_OFFSET],
> +	desc_buf[QUERY_DESC_MAX_SIZE] = '\0';
> +	strlcpy(dev_desc->model, (desc_buf + QUERY_DESC_HDR_SIZE),
> +		min_t(u8, desc_buf[QUERY_DESC_LENGTH_OFFSET],
>  		      MAX_MODEL_LEN));
> 
>  	/* Null terminate the model string */
>  	dev_desc->model[MAX_MODEL_LEN] = '\0';
> 
>  out:
> +	kfree(desc_buf);
>  	return err;
>  }
> 
> --
> 2.17.0


Looks good to me.
Reviewed-by: Subhash Jadavani <subhashj@...eaurora.org>

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