Bug 1400513 - u2f-hid-rs: fuzzers should use a deterministic cmd byte r=jcj

Summary: We're currently using the thread_rng to derive a cmd byte for the U2F protocol fuzzers. That of course should rather be derived deterministically from the input handed to the fuzzing target.

Bug #: 1400513

Differential Revision: https://phabricator.services.mozilla.com/D61

dom/webauthn/u2f-hid-rs/fuzz/fuzz_targets/u2f_read.rs

@@ -4,10 +4,8 @@
 
 #![no_main]
 #[macro_use] extern crate libfuzzer_sys;
-extern crate rand;
 extern crate u2fhid;
 
-use rand::{thread_rng, Rng};
 use std::{cmp, io};
 
 use u2fhid::{CID_BROADCAST, HID_RPT_SIZE};
@@ -59,7 +57,10 @@ impl<'a> U2FDevice for TestDevice<'a> {
 }
 
 fuzz_target!(|data: &[u8]| {
-    let mut dev = TestDevice::new(data);
-    let cmd = thread_rng().gen::<u8>();
-    let _ = sendrecv(&mut dev, cmd, data);
+    if data.len() > 0 {
+        let cmd = data[0];
+        let data = &data[1..];
+        let mut dev = TestDevice::new(data);
+        let _ = sendrecv(&mut dev, cmd, data);
+    }
 });

dom/webauthn/u2f-hid-rs/fuzz/fuzz_targets/u2f_read_write.rs

@@ -4,10 +4,8 @@
 
 #![no_main]
 #[macro_use] extern crate libfuzzer_sys;
-extern crate rand;
 extern crate u2fhid;
 
-use rand::{thread_rng, Rng};
 use std::{cmp, io};
 
 use u2fhid::{CID_BROADCAST, HID_RPT_SIZE};
@@ -60,8 +58,11 @@ impl U2FDevice for TestDevice {
 }
 
 fuzz_target!(|data: &[u8]| {
-    let mut dev = TestDevice::new();
-    let cmd = thread_rng().gen::<u8>();
-    let res = sendrecv(&mut dev, cmd, data);
-    assert_eq!(data, &res.unwrap()[..]);
+    if data.len() > 0 {
+        let cmd = data[0];
+        let data = &data[1..];
+        let mut dev = TestDevice::new();
+        let res = sendrecv(&mut dev, cmd, data);
+        assert_eq!(data, &res.unwrap()[..]);
+    }
 });