filesystem: ErrorCode::IsDirectory when opening directory with WRITE (#12136)

* filesystem: ErrorCode::IsDirectory when opening director w/o READ

On Windows, it was possible to return a directory descriptor if READ
wasn't in the permissions.  Fixes wasmtime for
WebAssembly/wasi-testsuite#176.

* Fix unused-variable error

* Fix the sense of the EISDIR compatibility hack

I had misremembered the nature of this incompatibility.
Fixed (hopefully) with a reference to POSIX.

prtest:full

* Update test expectations

prtest:full

* Update expectations for wasi-testsuite tests

path_open_preopen is now working on Windows.

* Possible fix for wasip1 file_open test

prtest:full

Author: wingo

crates/test-programs/src/bin/p1_path_open_preopen.rs

@@ -66,37 +66,23 @@ unsafe fn path_open_preopen() {
     )
     .expect("open with O_DIRECTORY and read right");
 
-    if !test_programs::preview1::config().errno_expect_windows() {
-        // Open OFLAGS_DIRECTORY and read/write rights should fail with isdir:
-        let err = wasip1::path_open(
-            FIRST_PREOPEN,
-            0,
-            ".",
-            wasip1::OFLAGS_DIRECTORY,
-            wasip1::RIGHTS_FD_READ | wasip1::RIGHTS_FD_WRITE,
-            0,
-            0,
-        )
-        .err()
-        .expect("open with O_DIRECTORY and read/write should fail");
-        assert_eq!(
-            err,
-            wasip1::ERRNO_ISDIR,
-            "opening directory read/write should fail with ISDIR"
-        );
-    } else {
-        // Open OFLAGS_DIRECTORY and read/write rights will succeed, only on windows:
-        let _ = wasip1::path_open(
-            FIRST_PREOPEN,
-            0,
-            ".",
-            wasip1::OFLAGS_DIRECTORY,
-            wasip1::RIGHTS_FD_READ | wasip1::RIGHTS_FD_WRITE,
-            0,
-            0,
-        )
-        .expect("open with O_DIRECTORY and read/write should succeed on windows");
-    }
+    // Open OFLAGS_DIRECTORY and read/write rights should fail with isdir:
+    let err = wasip1::path_open(
+        FIRST_PREOPEN,
+        0,
+        ".",
+        wasip1::OFLAGS_DIRECTORY,
+        wasip1::RIGHTS_FD_READ | wasip1::RIGHTS_FD_WRITE,
+        0,
+        0,
+    )
+    .err()
+    .expect("open with O_DIRECTORY and read/write should fail");
+    assert_eq!(
+        err,
+        wasip1::ERRNO_ISDIR,
+        "opening directory read/write should fail with ISDIR"
+    );
 }
 
 fn main() {

crates/wasi-common/src/snapshots/preview_1.rs

@@ -814,6 +814,13 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
         drop(dir_entry);
 
         let fd = match file {
+            // Paper over a divergence between Windows and POSIX, where
+            // POSIX returns EISDIR if you open a directory with the
+            // WRITE flag: https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html#:~:text=EISDIR
+            #[cfg(windows)]
+            OpenResult::Dir(_) if write => {
+                return Err(types::Errno::Isdir.into());
+            }
             OpenResult::File(file) => table.push(Arc::new(FileEntry::new(file, access_mode)))?,
             OpenResult::Dir(child_dir) => table.push(Arc::new(DirEntry::new(None, child_dir)))?,
         };

crates/wasi/src/filesystem.rs

@@ -1045,6 +1045,14 @@ impl Dir {
             .await?;
 
         match opened {
+            // Paper over a divergence between Windows and POSIX, where
+            // POSIX returns EISDIR if you open a directory with the
+            // WRITE flag: https://pubs.opengroup.org/onlinepubs/9699919799/functions/open.html#:~:text=EISDIR
+            #[cfg(windows)]
+            OpenResult::Dir(_) if flags.contains(DescriptorFlags::WRITE) => {
+                Err(ErrorCode::IsDirectory)
+            }
+
             OpenResult::Dir(dir) => Ok(Descriptor::Dir(Dir::new(
                 dir,
                 self.perms,

tests/wasi.rs

@@ -64,8 +64,6 @@ const KNOWN_FAILURES: &[&str] = &[
     #[cfg(windows)]
     "path_open_missing",
     #[cfg(windows)]
-    "path_open_preopen",
-    #[cfg(windows)]
     "path_open_read_write",
     #[cfg(windows)]
     "path_rename",