Validate CRC of incoming data

The data sent with Set_Report requests contains a CRC which we so far
ignored.  This patch adds a Crc struct that uses the CRC peripheral to
calculate the CRC for some data and uses it to validate the CRC of the
received data.

1 files changed, 13 insertions, 3 deletions

diff --git a/src/device.rs b/src/device.rs
index 0df14ae..fc119d5 100644
--- a/src/device.rs
+++ b/src/device.rs
@@ -7,6 +7,7 @@ use usb_device::bus::{UsbBus, UsbBusAllocator};
 use usb_device::device::{UsbDevice, UsbDeviceBuilder, UsbVidPid};
 
 use crate::commands::{CommandId, COMMAND_LEN};
+use crate::crc::Crc;
 use crate::hid::{HidDevice, Protocol, ReportType, Subclass};
 use crate::util::TryFrom;
 
@@ -85,14 +86,18 @@ impl Response {
 }
 
 pub struct Nitrokey {
+    crc: Crc,
     request: Option<Request>,
+    request_crc: u32,
     buf: [u8; REPORT_LEN],
 }
 
 impl Nitrokey {
-    pub fn new() -> Self {
+    pub fn new(crc: Crc) -> Self {
         Nitrokey {
+            crc,
             request: None,
+            request_crc: 0,
             buf: [0; REPORT_LEN],
         }
     }
@@ -118,12 +123,15 @@ impl HidDevice for Nitrokey {
 
         if let Some(ref request) = self.request {
             let mut response = Response::new(DeviceStatus::Ok, request.command_id, request.crc);
-            response.command_status =
+            response.command_status = if self.request_crc == request.crc {
                 if let Ok(command_id) = CommandId::try_from(request.command_id) {
                     command_id.execute(&request.data, &mut response.data)
                 } else {
                     CommandStatus::UnknownCommand
-                };
+                }
+            } else {
+                CommandStatus::WrongCrc
+            };
             // TODO: calculate actual CRC
             response.crc = 1; // libnitrokey accepts any non-zero value
 
@@ -146,6 +154,8 @@ impl HidDevice for Nitrokey {
         } else {
             let (request, len) = ssmarshal::deserialize(data).map_err(|_| ())?;
             assert!(len == REPORT_LEN);
+            // the last four bytes are ignored as they contain the CRC
+            self.request_crc = self.crc.get(&data[..REPORT_LEN - 4]);
             self.request = Some(request);
             Ok(())
         }