From c1be41bfbf01c7e427840e90f68c93f6adcfdd09 Mon Sep 17 00:00:00 2001
From: Rob Bradford <robert.bradford@intel.com>
Date: Mon, 22 Feb 2021 15:02:19 +0000
Subject: [PATCH] net_util: Replace use of rand crate with libc::getrandom()
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The rand crate provides a full cross platform true cryptographic random
number implementation. As such it brings it lots of othe dependencies
and increases our binary size and compile time. This is excessive for
generating a MAC address.

From the cargo tree output:

│   │   ├── rand v0.8.3
│   │   │   ├── libc v0.2.86
│   │   │   ├── rand_chacha v0.3.0
│   │   │   │   ├── ppv-lite86 v0.2.10
│   │   │   │   └── rand_core v0.6.0
│   │   │   │       └── getrandom v0.2.0
│   │   │   │           ├── cfg-if v0.1.10
│   │   │   │           └── libc v0.2.86
│   │   │   └── rand_core v0.6.0 (*)

And cargo bloat:

 0.0%   0.4% 40.4KiB rand_chacha rand_chacha::guts::refill_wide::impl_sse2
 0.0%   0.4% 40.0KiB rand_chacha rand_chacha::guts::refill_wide::impl_ssse3
 0.0%   0.3% 37.6KiB rand_chacha rand_chacha::guts::refill_wide::impl_avx
 0.0%   0.3% 37.2KiB rand_chacha rand_chacha::guts::refill_wide::impl_sse41
 0.0%   0.2% 26.1KiB rand_chacha rand_chacha::guts::refill_wide::impl_avx2

Signed-off-by: Rob Bradford <robert.bradford@intel.com>
---
 Cargo.lock          |  1 -
 net_util/Cargo.toml |  1 -
 net_util/src/lib.rs |  1 -
 net_util/src/mac.rs | 18 ++++++++++++++++--
 4 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index ffb11769e..55a36f3e2 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -702,7 +702,6 @@ dependencies = [
  "log 0.4.14",
  "net_gen",
  "pnet",
- "rand 0.8.3",
  "serde",
  "serde_json",
  "virtio-bindings",
diff --git a/net_util/Cargo.toml b/net_util/Cargo.toml
index 042515dc5..5b2721dbb 100644
--- a/net_util/Cargo.toml
+++ b/net_util/Cargo.toml
@@ -8,7 +8,6 @@ epoll = ">=4.0.1"
 libc = "0.2.86"
 log = "0.4.14"
 net_gen = { path = "../net_gen" }
-rand = "0.8.3"
 serde = "1.0.123"
 virtio-bindings = "0.1.0"
 vm-memory = { version = "0.5.0", features = ["backend-mmap", "backend-atomic"] }
diff --git a/net_util/src/lib.rs b/net_util/src/lib.rs
index 7d1320c4a..a226a4f64 100644
--- a/net_util/src/lib.rs
+++ b/net_util/src/lib.rs
@@ -14,7 +14,6 @@ extern crate libc;
 #[macro_use]
 extern crate log;
 extern crate net_gen;
-extern crate rand;
 extern crate serde;
 extern crate virtio_bindings;
 extern crate vm_memory;
diff --git a/net_util/src/mac.rs b/net_util/src/mac.rs
index ebf246d6b..548829a48 100644
--- a/net_util/src/mac.rs
+++ b/net_util/src/mac.rs
@@ -5,7 +5,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the THIRD-PARTY file.
 
-use rand::Rng;
 use std::fmt;
 use std::io;
 use std::result::Result;
@@ -82,7 +81,22 @@ impl MacAddr {
 
     pub fn local_random() -> MacAddr {
         // Generate a fully random MAC
-        let mut random_bytes = rand::thread_rng().gen::<[u8; MAC_ADDR_LEN]>();
+        let mut random_bytes = [0u8; MAC_ADDR_LEN];
+        unsafe {
+            // Man page says this function will not be interrupted by a signal
+            // for requests less than 256 bytes
+            if libc::getrandom(
+                random_bytes.as_mut_ptr() as *mut _ as *mut libc::c_void,
+                MAC_ADDR_LEN,
+                0,
+            ) < 0
+            {
+                error!(
+                    "Error populating MAC address with random data: {}",
+                    std::io::Error::last_os_error()
+                )
+            }
+        };
 
         // Set the first byte to make the OUI a locally administered OUI
         random_bytes[0] = 0x2e;