Use Box<[T]> instead of Vec<T> to initialize and drop ArrayQueue

Previously, the queue buffer was initialized using Vec::with_capacity.
Note the with_capacity does not guarantee that precise capacity;
the actual layout of the allocated memory could have a greater size.

The drop code assumed the buffer has a size
equal to the queue's capacity. This is undefined
behavior when the buffer actually has a greater size.

Using Box<[T]> instead guarantees an exact capacity, resolving the UB.

crossbeam-channel/src/flavors/array.rs

@@ -115,7 +115,7 @@ impl<T> Channel<T> {
         // Allocate a buffer of `cap` slots initialized
         // with stamps.
         let buffer = {
-            let mut v: Vec<Slot<T>> = (0..cap)
+            let mut boxed: Box<[Slot<T>]> = (0..cap)
                 .map(|i| {
                     // Set the stamp to `{ lap: 0, mark: 0, index: i }`.
                     Slot {
@@ -124,8 +124,8 @@ impl<T> Channel<T> {
                     }
                 })
                 .collect();
-            let ptr = v.as_mut_ptr();
-            mem::forget(v);
+            let ptr = boxed.as_mut_ptr();
+            mem::forget(boxed);
             ptr
         };
 
@@ -553,7 +553,11 @@ impl<T> Drop for Channel<T> {
 
         // Finally, deallocate the buffer, but don't run any destructors.
         unsafe {
-            Vec::from_raw_parts(self.buffer, 0, self.cap);
+            // Create a slice from the buffer to make
+            // a fat pointer. Then, use Box::from_raw
+            // to deallocate it.
+            let ptr = std::slice::from_raw_parts_mut(self.buffer, self.cap) as *mut [Slot<T>];
+            Box::from_raw(ptr);
         }
     }
 }

crossbeam-queue/src/array_queue.rs

@@ -8,7 +8,7 @@
 //!   - Simplified BSD License and Apache License, Version 2.0
 //!   - http://www.1024cores.net/home/code-license
 
-use alloc::vec::Vec;
+use alloc::boxed::Box;
 use core::cell::UnsafeCell;
 use core::fmt;
 use core::marker::PhantomData;
@@ -110,7 +110,7 @@ impl<T> ArrayQueue<T> {
         // Allocate a buffer of `cap` slots initialized
         // with stamps.
         let buffer = {
-            let mut v: Vec<Slot<T>> = (0..cap)
+            let mut boxed: Box<[Slot<T>]> = (0..cap)
                 .map(|i| {
                     // Set the stamp to `{ lap: 0, index: i }`.
                     Slot {
@@ -119,8 +119,8 @@ impl<T> ArrayQueue<T> {
                     }
                 })
                 .collect();
-            let ptr = v.as_mut_ptr();
-            mem::forget(v);
+            let ptr = boxed.as_mut_ptr();
+            mem::forget(boxed);
             ptr
         };
 
@@ -425,7 +425,11 @@ impl<T> Drop for ArrayQueue<T> {
 
         // Finally, deallocate the buffer, but don't run any destructors.
         unsafe {
-            Vec::from_raw_parts(self.buffer, 0, self.cap);
+            // Create a slice from the buffer to make
+            // a fat pointer. Then, use Box::from_raw
+            // to deallocate it.
+            let ptr = std::slice::from_raw_parts_mut(self.buffer, self.cap) as *mut [Slot<T>];
+            Box::from_raw(ptr);
         }
     }
 }