Replace AHash (DoS-resistant) by FxHash (simpler dependency)

In the datetime module, we hash a set of keys known at compile time and hence
are not subject to DoS issues.

In the borrow module, the keys include pointer addresses which means that even
if a program exposes its usage of NumPy arrays to remote user control, a DoS
attack would also need detailed control over the placement of memory allocations
in which case outright memory exhaustion seems to be a simpler avenue of attack.

Author: adamreichold

Cargo.toml

@@ -15,7 +15,6 @@ keywords = ["python", "numpy", "ffi", "pyo3"]
 license = "BSD-2-Clause"
 
 [dependencies]
-ahash = "0.7"
 half = { version = "2.0", default-features = false, optional = true }
 libc = "0.2"
 nalgebra = { version = "0.31", default-features = false, optional = true }
@@ -24,6 +23,7 @@ num-integer = "0.1"
 num-traits = "0.2"
 ndarray = ">= 0.13, < 0.16"
 pyo3 = { version = "0.17", default-features = false, features = ["macros"] }
+rustc-hash = "1.1"
 
 [dev-dependencies]
 pyo3 = { version = "0.17", default-features = false, features = ["auto-initialize"] }

src/borrow.rs

@@ -167,12 +167,12 @@ use std::fmt;
 use std::mem::size_of;
 use std::ops::Deref;
 
-use ahash::AHashMap;
 use ndarray::{
     ArrayView, ArrayViewMut, Dimension, IntoDimension, Ix1, Ix2, Ix3, Ix4, Ix5, Ix6, IxDyn,
 };
 use num_integer::gcd;
 use pyo3::{FromPyObject, PyAny, PyResult, Python};
+use rustc_hash::FxHashMap;
 
 use crate::array::PyArray;
 use crate::cold;
@@ -237,7 +237,7 @@ impl BorrowKey {
     }
 }
 
-type BorrowFlagsInner = AHashMap<*mut u8, AHashMap<BorrowKey, isize>>;
+type BorrowFlagsInner = FxHashMap<*mut u8, FxHashMap<BorrowKey, isize>>;
 
 struct BorrowFlags(UnsafeCell<Option<BorrowFlagsInner>>);
 
@@ -250,7 +250,7 @@ impl BorrowFlags {
 
     #[allow(clippy::mut_from_ref)]
     unsafe fn get(&self) -> &mut BorrowFlagsInner {
-        (*self.0.get()).get_or_insert_with(AHashMap::new)
+        (*self.0.get()).get_or_insert_with(Default::default)
     }
 
     fn acquire(&self, _py: Python, address: *mut u8, key: BorrowKey) -> Result<(), BorrowError> {
@@ -287,7 +287,8 @@ impl BorrowFlags {
                 }
             }
             Entry::Vacant(entry) => {
-                let mut same_base_arrays = AHashMap::with_capacity(1);
+                let mut same_base_arrays =
+                    FxHashMap::with_capacity_and_hasher(1, Default::default());
                 same_base_arrays.insert(key, 1);
                 entry.insert(same_base_arrays);
             }
@@ -349,7 +350,8 @@ impl BorrowFlags {
                 }
             }
             Entry::Vacant(entry) => {
-                let mut same_base_arrays = AHashMap::with_capacity(1);
+                let mut same_base_arrays =
+                    FxHashMap::with_capacity_and_hasher(1, Default::default());
                 same_base_arrays.insert(key, -1);
                 entry.insert(same_base_arrays);
             }

src/datetime.rs

@@ -63,8 +63,8 @@ use std::fmt;
 use std::hash::Hash;
 use std::marker::PhantomData;
 
-use ahash::AHashMap;
 use pyo3::{Py, Python};
+use rustc_hash::FxHashMap;
 
 use crate::dtype::{Element, PyArrayDescr};
 use crate::npyffi::{PyArray_DatetimeDTypeMetaData, NPY_DATETIMEUNIT, NPY_TYPES};
@@ -206,7 +206,7 @@ impl<U: Unit> fmt::Debug for Timedelta<U> {
 
 struct TypeDescriptors {
     npy_type: NPY_TYPES,
-    dtypes: UnsafeCell<Option<AHashMap<NPY_DATETIMEUNIT, Py<PyArrayDescr>>>>,
+    dtypes: UnsafeCell<Option<FxHashMap<NPY_DATETIMEUNIT, Py<PyArrayDescr>>>>,
 }
 
 unsafe impl Sync for TypeDescriptors {}
@@ -221,8 +221,8 @@ impl TypeDescriptors {
     }
 
     #[allow(clippy::mut_from_ref)]
-    unsafe fn get(&self) -> &mut AHashMap<NPY_DATETIMEUNIT, Py<PyArrayDescr>> {
-        (*self.dtypes.get()).get_or_insert_with(AHashMap::new)
+    unsafe fn get(&self) -> &mut FxHashMap<NPY_DATETIMEUNIT, Py<PyArrayDescr>> {
+        (*self.dtypes.get()).get_or_insert_with(Default::default)
     }
 
     #[allow(clippy::wrong_self_convention)]