From 4d293c33be8ac6d56bf14a2dba2235602d310336 Mon Sep 17 00:00:00 2001
From: NathanW <nathansward@comcast.net>
Date: Mon, 19 Apr 2021 14:29:57 -0600
Subject: [PATCH] [bevy_core/bytes] Fix UB with accessing memory with incorrect
 alignment

---
 crates/bevy_core/src/bytes.rs | 34 ++++++++++++++++++++++------------
 1 file changed, 22 insertions(+), 12 deletions(-)

diff --git a/crates/bevy_core/src/bytes.rs b/crates/bevy_core/src/bytes.rs
index f5846c67bce56..b18ee94d72275 100644
--- a/crates/bevy_core/src/bytes.rs
+++ b/crates/bevy_core/src/bytes.rs
@@ -46,14 +46,16 @@ pub trait FromBytes {
 
 impl<T> FromBytes for T
 where
-    T: Byteable + Clone,
+    T: Byteable + Copy,
 {
     fn from_bytes(bytes: &[u8]) -> Self {
-        unsafe {
-            let byte_ptr = bytes.as_ptr();
-            let ptr = byte_ptr as *const Self;
-            (*ptr).clone()
-        }
+        assert_eq!(
+            bytes.len(),
+            std::mem::size_of::<T>(),
+            "Cannot convert byte slice `&[u8]` to type `{}`. They are not the same size.",
+            std::any::type_name::<T>()
+        );
+        unsafe { bytes.as_ptr().cast::<T>().read_unaligned() }
     }
 }
 
@@ -62,7 +64,7 @@ where
     T: Byteable,
 {
     fn as_bytes(&self) -> &[u8] {
-        let len = std::mem::size_of_val(self);
+        let len = std::mem::size_of::<T>();
         unsafe { core::slice::from_raw_parts(self as *const Self as *const u8, len) }
     }
 }
@@ -166,15 +168,23 @@ where
 
 impl<T> FromBytes for Vec<T>
 where
-    T: Sized + Clone + Byteable,
+    T: Sized + Copy + Byteable,
 {
     fn from_bytes(bytes: &[u8]) -> Self {
+        assert_eq!(
+            bytes.len() % std::mem::size_of::<T>(),
+            0,
+            "Cannot convert byte slice `&[u8]` to type `Vec<{0}>`. Slice length is not a multiple of std::mem::size_of::<{0}>.",
+            std::any::type_name::<T>(),
+        );
+
+        let len = bytes.len() / std::mem::size_of::<T>();
+        let mut vec = Vec::<T>::with_capacity(len);
         unsafe {
-            let byte_ptr = bytes.as_ptr() as *const T;
-            let len = bytes.len() / std::mem::size_of::<T>();
-            let slice = core::slice::from_raw_parts::<T>(byte_ptr, len);
-            slice.to_vec()
+            std::ptr::copy_nonoverlapping(bytes.as_ptr(), vec.as_mut_ptr() as *mut u8, bytes.len());
+            vec.set_len(len);
         }
+        vec
     }
 }