Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 40 insertions, 0 deletions

diff --git a/third_party/rust/constant_time_eq/src/lib.rs b/third_party/rust/constant_time_eq/src/lib.rs
new file mode 100644
index 0000000000..27a2d27a1a
--- /dev/null
+++ b/third_party/rust/constant_time_eq/src/lib.rs
@@ -0,0 +1,40 @@
+#![no_std]
+
+// This function is non-inline to prevent the optimizer from looking inside it.
+#[inline(never)]
+fn constant_time_ne(a: &[u8], b: &[u8]) -> u8 {
+    assert!(a.len() == b.len());
+
+    // These useless slices make the optimizer elide the bounds checks.
+    // See the comment in clone_from_slice() added on Rust commit 6a7bc47.
+    let len = a.len();
+    let a = &a[..len];
+    let b = &b[..len];
+
+    let mut tmp = 0;
+    for i in 0..len {
+        tmp |= a[i] ^ b[i];
+    }
+    tmp // The compare with 0 must happen outside this function.
+}
+
+/// Compares two equal-sized byte strings in constant time.
+///
+/// # Examples
+///
+/// ```
+/// use constant_time_eq::constant_time_eq;
+///
+/// assert!(constant_time_eq(b"foo", b"foo"));
+/// assert!(!constant_time_eq(b"foo", b"bar"));
+/// assert!(!constant_time_eq(b"bar", b"baz"));
+/// # assert!(constant_time_eq(b"", b""));
+///
+/// // Not equal-sized, so won't take constant time.
+/// assert!(!constant_time_eq(b"foo", b""));
+/// assert!(!constant_time_eq(b"foo", b"quux"));
+/// ```
+#[inline]
+pub fn constant_time_eq(a: &[u8], b: &[u8]) -> bool {
+    a.len() == b.len() && constant_time_ne(a, b) == 0
+}