Unsound sending of non-Send types in threadalone, patched (#1858)

* Add advisory for threadalone

* Fix filename

crates/threadalone/RUSTSEC-0000-0000.md

@@ -0,0 +1,28 @@
+```toml
+[advisory]
+id = "RUSTSEC-0000-0000"
+package = "threadalone"
+date = "2024-01-07"
+url = "https://github.com/cr0sh/threadalone/issues/1"
+informational = "unsound"
+
+[versions]
+patched = [">= 0.2.1"]
+```
+
+# Unsound sending of non-Send types across threads
+
+Affected versions can run the `Drop` impl of a non-Send type on a different
+thread than it was created on.
+
+The flaw occurs when a stderr write performed by the `threadalone` crate fails,
+for example because stderr is redirected to a location on a filesystem that is
+full, or because stderr is a pipe that has been closed by the reader.
+
+Dropping a non-Send type on the wrong thread is unsound. If used with a type
+such as a pthread-based `MutexGuard`, [the consequence is undefined
+behavior][mutexguard]. If used with `Rc`, there would be a data race on the
+reference count, which is likewise undefined behavior.
+
+[mutexguard]: https://github.com/rust-lang/rust/issues/23465#issuecomment-82730326
+