mfd: cros_ec: Use a zero-length array for command data

Hello Javier Martinez Canillas,

The patch a841178445bb: "mfd: cros_ec: Use a zero-length array for command data" from Jun 9, 2015, has memory corruption issues.

drivers/platform/chrome/cros_ec_dev.c
130 static long ec_device_ioctl_xcmd(struct cros_ec_dev *ec, void __user *arg) 131 {

   132          long ret;
   133          struct cros_ec_command u_cmd;
   134          struct cros_ec_command *s_cmd;
   135
   136          if (copy_from_user(&u_cmd, arg, sizeof(u_cmd)))
   137                  return -EFAULT;
   138
   139          s_cmd = kmalloc(sizeof(*s_cmd) + max(u_cmd.outsize, u_cmd.insize),
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This can integer overflow on 32 bit systems leading to a smaller s_cmd than intended.

140 GFP_KERNEL);
141 if (!s_cmd)
142 return -ENOMEM;
143

   144          if (copy_from_user(s_cmd, arg, sizeof(*s_cmd) + u_cmd.outsize)) {
                                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Memory corruption.

   145                  ret = -EFAULT;
   146                  goto exit;
   147          }
   148

regards,
dan carpenter