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

Javier Martinez Canillas
2015-05-05T16:11:34Z

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