From fff15380539c659ccdb03fcc192eb95578b1feb5 Mon Sep 17 00:00:00 2001
From: Jeff Vander Stoep <jeffv@google.com>
Date: Thu, 1 Dec 2022 11:29:41 +0100
Subject: [PATCH] Use /dev/urandom instead of getrandom()

To generate the ahash crate's default hash keys, use /dev/urandom
instead of getrandom() to avoid blocking boot on systems where the
entropy pool isn't initialized in time and where the use case of this
crate doesn't actually require cryptographic randomness.

If opening or reading from /dev/urandom fails, fall back to getrandom().

Note that std::collections::HashMap doesn't block for randomness either,
for the same reason.  So this change just makes ahash work like HashMap.

Bug: 185934601
Change-Id: Ieaf4bcfde5664d0b5d845234d0c2139d89c4153c
---
 src/random_state.rs | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/random_state.rs b/src/random_state.rs
index e885fa4..5b85726 100644
--- a/src/random_state.rs
+++ b/src/random_state.rs
@@ -48,6 +48,15 @@ pub(crate) const PI2: [u64; 4] = [
     0x3f84_d5b5_b547_0917,
 ];
 
+#[cfg(all(feature = "runtime-rng", not(all(feature = "compile-time-rng", test))))]
+fn read_urandom(dest: &mut [u8]) -> Result<(), std::io::Error> {
+    use std::fs::File;
+    use std::io::Read;
+
+    let mut f = File::open("/dev/urandom")?;
+    f.read_exact(dest)
+}
+
 cfg_if::cfg_if! {
     if #[cfg(all(feature = "compile-time-rng", any(test, fuzzing)))] {
         #[inline]
@@ -78,7 +87,9 @@ cfg_if::cfg_if! {
 
             SEEDS.get_or_init(|| {
                 let mut result: [u8; 64] = [0; 64];
-                getrandom::getrandom(&mut result).expect("getrandom::getrandom() failed.");
+                if read_urandom(&mut result).is_err() {
+                    getrandom::getrandom(&mut result).expect("getrandom::getrandom() failed.");
+                }
                 Box::new(result.convert())
             })
         }
-- 
2.38.1.584.g0f3c55d4c2-goog