Added an API for contributing randomness to the kernel (#224)

build.rs

@@ -24,6 +24,7 @@ const INCLUDED_FUNCTIONS: &[&str] = &[
     "wait_for_random_bytes",
     "get_random_bytes",
     "rng_is_initialized",
+    "add_device_randomness",
 ];
 const INCLUDED_VARS: &[&str] = &[
     "EINVAL",

src/random.rs

@@ -30,3 +30,14 @@ pub fn getrandom_nonblock(dest: &mut [u8]) -> error::KernelResult<()> {
     }
     getrandom(dest)
 }
+
+/// Contributes the contents of `data` to the kernel's entropy pool. Does _not_
+/// credit the kernel entropy counter though.
+pub fn add_randomness(data: &[u8]) {
+    unsafe {
+        bindings::add_device_randomness(
+            data.as_ptr() as *const c_types::c_void,
+            data.len().try_into().unwrap(),
+        );
+    }
+}

tests/random/src/lib.rs

@@ -8,8 +8,9 @@ use linux_kernel_module::{self, cstr, random, Mode};
 struct EntropySource;
 
 impl SysctlStorage for EntropySource {
-    fn store_value(&self, _data: &[u8]) -> (usize, linux_kernel_module::KernelResult<()>) {
-        (0, Err(linux_kernel_module::Error::EINVAL))
+    fn store_value(&self, data: &[u8]) -> (usize, linux_kernel_module::KernelResult<()>) {
+        random::add_randomness(data);
+        (data.len(), Ok(()))
     }
 
     fn read_value(
@@ -35,7 +36,7 @@ impl linux_kernel_module::KernelModule for RandomTestModule {
                 cstr!("rust/random-tests"),
                 cstr!("entropy"),
                 EntropySource,
-                Mode::from_int(0o444),
+                Mode::from_int(0o666),
             )?,
         })
     }

tests/random/tests/tests.rs

@@ -5,7 +5,7 @@ use std::io::Read;
 use kernel_module_testlib::with_kernel_module;
 
 #[test]
-fn test_random_entropy() {
+fn test_random_entropy_read() {
     with_kernel_module(|| {
         let mut keys = HashSet::new();
         for _ in 0..1024 {
@@ -17,3 +17,10 @@ fn test_random_entropy() {
         assert_eq!(keys.len(), 1024);
     });
 }
+
+#[test]
+fn test_random_entropy_write() {
+    with_kernel_module(|| {
+        fs::write("/proc/sys/rust/random-tests/entropy", b"1234567890").unwrap();
+    });
+}