Re: [Intel-wired-lan] [PATCH v3 iwl-next] i40e: Use correct buffer size in i40e_dbg_command_read

[Alexander Lobakin]

From: Kunwu Chan <chen...@kylinos.cn>
Date: Mon, 4 Dec 2023 09:44:55 +0800

> The size of "i40e_dbg_command_buf" is 256, the size of "name"
> depends on "IFNAMSIZ", plus a null character and format size,
> the total size is more than 256.
> 
> Improve readability and maintainability by replacing a hardcoded string
> allocation and formatting by the use of the kasprintf() helper.
> 
> Fixes: 02e9c290814c ("i40e: debugfs interface")
> Signed-off-by: Kunwu Chan <chen...@kylinos.cn>
> Suggested-by: Simon Horman <ho...@kernel.org>
> Suggested-by: Alexander Lobakin <aleksander.loba...@intel.com>
> ---
> v2
>    - Update the size calculation with IFNAMSIZ and 
> sizeof(i40e_dbg_command_buf)
> v3
>    - Use kasprintf to improve readability and maintainability
> ---
>  drivers/net/ethernet/intel/i40e/i40e_debugfs.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c 
> b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
> index 88240571721a..a176de89de9c 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_debugfs.c
> @@ -72,23 +72,22 @@ static ssize_t i40e_dbg_command_read(struct file *filp, 
> char __user *buffer,
>  {
>       struct i40e_pf *pf = filp->private_data;
>       int bytes_not_copied;
> -     int buf_size = 256;
> -     char *buf;
> +     char *buf = NULL;

This is unneeded.

>       int len;
>  
>       /* don't allow partial reads */
>       if (*ppos != 0)
>               return 0;
> -     if (count < buf_size)
> -             return -ENOSPC;
>  
> -     buf = kzalloc(buf_size, GFP_KERNEL);
> +     buf = kasprintf(GFP_KERNEL, "%s: %s\n",
> +                     pf->vsi[pf->lan_vsi]->netdev->name,
> +                     i40e_dbg_command_buf);
>       if (!buf)
>               return -ENOSPC;
>  
> -     len = snprintf(buf, buf_size, "%s: %s\n",
> -                    pf->vsi[pf->lan_vsi]->netdev->name,
> -                    i40e_dbg_command_buf);
> +     len = strlen(buf);

strlen() doesn't include the terminating '\0', but you need to copy it
as well. Hence `strlen(buf) + 1`.

> +     if (count < len)
> +             return -ENOSPC;

Here you have memory leak in case the condition is true.

>  
>       bytes_not_copied = copy_to_user(buffer, buf, len);
>       kfree(buf);

Taking the above two into account, I'd suggest doing something like:

        if (!buf)
                return -ENOSPC;

        len = strlen(buf) + 1;

        if (count < len)
                bytes_not_copied = -ENOSPC;
        elseif (copy_to_user(buffer, buf, len))
                bytes_not_copied = -EFAULT;
        else
                bytes_not_copied = 0;

        kfree(buf);

        if (bytes_not_copied)
                return bytes_not_copied;

        *ppos = len;

        return len;
}

Thanks,
Olek
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