Disallow opening directory with rights::fd_write

This commit changes `path_open` such that opening an existing directory
with the `rights::fd_write` flag set returns an error `isdir`.  This
behavior is consistent with other runtimes.

fixes #4766

lib/wasix/src/syscalls/wasi/path_open.rs

@@ -273,8 +273,12 @@ pub(crate) fn path_open_internal(
                     return Ok(Err(Errno::Notcapable));
                 }
             }
-            Kind::Dir { .. }
-            | Kind::Socket { .. }
+            Kind::Dir { .. } => {
+                if fs_rights_base.contains(Rights::FD_WRITE) {
+                    return Ok(Err(Errno::Isdir));
+                }
+            }
+            Kind::Socket { .. }
             | Kind::Pipe { .. }
             | Kind::EventNotifications { .. }
             | Kind::Epoll { .. } => {}

tests/wasi-fyi/fs_open_dir_write.rs

@@ -0,0 +1,39 @@
+#[link(wasm_import_module = "wasi_snapshot_preview1")]
+extern "C" {
+    pub fn path_open(
+        fd: i32,
+        dirflags: i32,
+        path: i32,
+        path_len: i32,
+        oflags: i32,
+        fs_rights_base: i64,
+        fs_rights_inheriting: i64,
+        fdflags: i32,
+        result_fd: i32,
+    ) -> i32;
+}
+
+const ERRNO_ISDIR: i32 = 31;
+const RIGHTS_FD_WRITE: i64 = 64;
+
+fn main() {
+    unsafe {
+        let base_fd = 5;
+        let path = "fyi/fs_open_dir_write.dir";
+        let errno = path_open(
+            base_fd,
+            0,
+            path.as_ptr() as i32,
+            path.as_bytes().len() as i32,
+            0,
+            RIGHTS_FD_WRITE,
+            0,
+            0,
+            1024,
+        );
+        assert_eq!(
+            errno, ERRNO_ISDIR,
+            "opening a dir with rights::fd_write should fail"
+        );
+    }
+}