Backport rust-lang/git2-rs#1213 to git2 0.20.x

CHANGELOG.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 0.20.4 - 2026-02-02
+[0.20.3...0.20.4](https://github.com/rust-lang/git2-rs/compare/git2-0.20.3...git2-0.20.4)
+
+### Fixed
+
+- Fix undefined behavior when dereferencing empty `Buf`.
+  [#1213](https://github.com/rust-lang/git2-rs/pull/1213)
+
 ## 0.20.3 - 2025-12-06
 [0.20.2...0.20.3](https://github.com/rust-lang/git2-rs/compare/git2-0.20.2...git2-0.20.3)
 

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "git2"
-version = "0.20.3"
+version = "0.20.4"
 authors = ["Josh Triplett <josh@joshtriplett.org>", "Alex Crichton <alex@alexcrichton.com>"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"

src/buf.rs

@@ -44,12 +44,18 @@ impl Buf {
 impl Deref for Buf {
     type Target = [u8];
     fn deref(&self) -> &[u8] {
+        if self.raw.ptr.is_null() {
+            return &[];
+        }
         unsafe { slice::from_raw_parts(self.raw.ptr as *const u8, self.raw.size as usize) }
     }
 }
 
 impl DerefMut for Buf {
     fn deref_mut(&mut self) -> &mut [u8] {
+        if self.raw.ptr.is_null() {
+            return &mut [];
+        }
         unsafe { slice::from_raw_parts_mut(self.raw.ptr as *mut u8, self.raw.size as usize) }
     }
 }
@@ -69,3 +75,12 @@ impl Drop for Buf {
         unsafe { raw::git_buf_dispose(&mut self.raw) }
     }
 }
+
+#[test]
+fn empty_buf() {
+    let mut buf = Buf::new();
+    let x: &[u8] = &*buf;
+    assert_eq!(x.len(), 0);
+    let x: &mut [u8] = &mut *buf;
+    assert_eq!(x.len(), 0);
+}