Re: [RESEND PATCH 4/8] mfd: cros_ec: Use a zero-length array for command data

[Javier Martinez Canillas <javier.martinez@collabora.co.uk>]

Hello Gwendal,

On 04/24/2015 10:29 PM, Gwendal Grignou wrote:
> On Mon, Apr 6, 2015 at 9:15 AM, Javier Martinez Canillas
> <javier.martinez@collabora.co.uk> wrote:

[snip]

>>
>> @@ -110,17 +115,25 @@ static ssize_t ec_device_read(struct file *filp, char __user *buffer,
>>  static long ec_device_ioctl_xcmd(struct cros_ec_device *ec, void __user *arg)
>>  {
>>         long ret;
>> -       struct cros_ec_command s_cmd = { };
>> +       int len;
>> +       struct cros_ec_command *u_cmd = arg;
>> +       struct cros_ec_command *s_cmd;
>> +
>> +       len = max(u_cmd->outsize, u_cmd->insize);
> It does not work, u_cmd is not accessible yet. You should do:
> struct cros_ec_command u_cmd;
> if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
>   return -EFAULT;
> len = max(u_cmd.outsize, u_cmd.insize);
> 
>

Right, I'll change that.
 
>> +
>> +       s_cmd = kzalloc(sizeof(*s_cmd) + len, GFP_KERNEL);
>> +       if (!s_cmd)
>> +               return -ENOMEM;
>>
>> -       if (copy_from_user(&s_cmd, arg, sizeof(s_cmd)))
>> +       if (copy_from_user(s_cmd, arg, sizeof(*s_cmd) + len))
> sizeof(*s_cmd) + u_cmd.outsize is good enough.

Ok.

>>                 return -EFAULT;
>>
>> -       ret = cros_ec_cmd_xfer(ec, &s_cmd);
>> +       ret = cros_ec_cmd_xfer(ec, s_cmd);
>>         /* Only copy data to userland if data was received. */
>>         if (ret < 0)
>>                 return ret;
>>
>> -       if (copy_to_user(arg, &s_cmd, sizeof(s_cmd)))
>> +       if (copy_to_user(arg, s_cmd, sizeof(*s_cmd) + len))
> sizeof(*s_cmd) + min(ret, u_cmd.insize) is safer

Sure.

>>                 return -EFAULT;
>>
>>         return 0;
> I missed this one earlier. Tools expect the number of byte read, so it should be
> return ret;
> 

Ok, I'll change that as well.

Thanks a lot for your feedback!

Best regards,
Javier