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BTree: fix untrue safety #82439

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Mar 3, 2021
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BTree: fix untrue safety #82439

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31 changes: 15 additions & 16 deletions library/alloc/src/collections/btree/node.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -78,9 +78,8 @@ impl<K, V> LeafNode<K, V> {
}
}

/// Creates a new boxed `LeafNode`. Unsafe because all nodes should really be hidden behind
/// `BoxedNode`, preventing accidental dropping of uninitialized keys and values.
unsafe fn new() -> Box<Self> {
/// Creates a new boxed `LeafNode`.
fn new() -> Box<Self> {
unsafe {
let mut leaf = Box::new_uninit();
LeafNode::init(leaf.as_mut_ptr());
Expand Down Expand Up @@ -108,10 +107,9 @@ struct InternalNode<K, V> {
impl<K, V> InternalNode<K, V> {
/// Creates a new boxed `InternalNode`.
///
/// This is unsafe for two reasons. First, it returns an owned `InternalNode` in a box, risking
/// dropping of uninitialized fields. Second, an invariant of internal nodes is that `len + 1`
/// edges are initialized and valid, meaning that even when the node is empty (having a
/// `len` of 0), there must be one initialized and valid edge. This function does not set up
/// # Safety
/// An invariant of internal nodes is that they have at least one
/// initialized and valid edge. This function does not set up
/// such an edge.
unsafe fn new() -> Box<Self> {
unsafe {
Expand Down Expand Up @@ -145,7 +143,7 @@ impl<K, V> Root<K, V> {

impl<K, V> NodeRef<marker::Owned, K, V, marker::Leaf> {
fn new_leaf() -> Self {
Self::from_new_leaf(unsafe { LeafNode::new() })
Self::from_new_leaf(LeafNode::new())
}

fn from_new_leaf(leaf: Box<LeafNode<K, V>>) -> Self {
Expand All @@ -157,10 +155,13 @@ impl<K, V> NodeRef<marker::Owned, K, V, marker::Internal> {
fn new_internal(child: Root<K, V>) -> Self {
let mut new_node = unsafe { InternalNode::new() };
new_node.edges[0].write(child.node);
NodeRef::from_new_internal(new_node, child.height + 1)
unsafe { NodeRef::from_new_internal(new_node, child.height + 1) }
}

fn from_new_internal(internal: Box<InternalNode<K, V>>, height: usize) -> Self {
/// # Safety
/// `height` must not be zero.
unsafe fn from_new_internal(internal: Box<InternalNode<K, V>>, height: usize) -> Self {
debug_assert!(height > 0);
let node = NonNull::from(Box::leak(internal)).cast();
let mut this = NodeRef { height, node, _marker: PhantomData };
this.borrow_mut().correct_all_childrens_parent_links();
Expand Down Expand Up @@ -1086,14 +1087,12 @@ impl<'a, K: 'a, V: 'a> Handle<NodeRef<marker::Mut<'a>, K, V, marker::Leaf>, mark
/// - All the key-value pairs to the right of this handle are put into a newly
/// allocated node.
pub fn split(mut self) -> SplitResult<'a, K, V, marker::Leaf> {
unsafe {
let mut new_node = LeafNode::new();
let mut new_node = LeafNode::new();

let kv = self.split_leaf_data(&mut new_node);
let kv = self.split_leaf_data(&mut new_node);

let right = NodeRef::from_new_leaf(new_node);
SplitResult { left: self.node, kv, right }
}
let right = NodeRef::from_new_leaf(new_node);
SplitResult { left: self.node, kv, right }
}

/// Removes the key-value pair pointed to by this handle and returns it, along with the edge
Expand Down