fix: respect fd_prestat_dir_name path_max_len argument (#6444)

prtest:full

Signed-off-by: Roman Volosatovs <[email protected]>

crates/test-programs/wasi-tests/src/bin/dir_fd_op_failures.rs

@@ -5,6 +5,22 @@ unsafe fn test_fd_dir_ops(dir_fd: wasi::Fd) {
     let stat = wasi::fd_filestat_get(dir_fd).expect("failed to fdstat");
     assert_eq!(stat.filetype, wasi::FILETYPE_DIRECTORY);
 
+    let (pr_fd, pr_name_len) = (3..)
+        .map_while(|fd| wasi::fd_prestat_get(fd).ok().map(|stat| (fd, stat)))
+        .find_map(|(fd, wasi::Prestat { tag, u })| {
+            (tag == wasi::PREOPENTYPE_DIR.raw()).then_some((fd, u.dir.pr_name_len))
+        })
+        .expect("failed to find preopen directory");
+
+    let mut pr_name = vec![];
+    let r = wasi::fd_prestat_dir_name(pr_fd, pr_name.as_mut_ptr(), 0);
+    assert_eq!(r, Err(wasi::ERRNO_NAMETOOLONG));
+
+    // Test that passing a larger than necessary buffer works correctly
+    let mut pr_name = vec![0; pr_name_len + 1];
+    let r = wasi::fd_prestat_dir_name(pr_fd, pr_name.as_mut_ptr(), pr_name_len + 1);
+    assert_eq!(r, Ok(()));
+
     let mut read_buf = vec![0; 128].into_boxed_slice();
     let iovec = wasi::Iovec {
         buf: read_buf.as_mut_ptr(),

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

@@ -509,7 +509,7 @@ impl wasi_snapshot_preview1::WasiSnapshotPreview1 for WasiCtx {
                 .ok_or_else(|| Error::not_supported())?
                 .as_bytes();
             let path_len = path_bytes.len();
-            if path_len < path_max_len as usize {
+            if path_len > path_max_len as usize {
                 return Err(Error::name_too_long());
             }
             path.as_array(path_len as u32).copy_from_slice(path_bytes)?;

crates/wasi-preview1-component-adapter/src/lib.rs

@@ -743,10 +743,10 @@ pub unsafe extern "C" fn fd_prestat_get(fd: Fd, buf: *mut Prestat) -> Errno {
 
 /// Return a description of the given preopened file descriptor.
 #[no_mangle]
-pub unsafe extern "C" fn fd_prestat_dir_name(fd: Fd, path: *mut u8, path_len: Size) -> Errno {
+pub unsafe extern "C" fn fd_prestat_dir_name(fd: Fd, path: *mut u8, path_max_len: Size) -> Errno {
     State::with(|state| {
         if let Some(preopen) = state.descriptors().get_preopen(fd) {
-            if preopen.path.len < path_len as usize {
+            if preopen.path.len > path_max_len as usize {
                 Err(ERRNO_NAMETOOLONG)
             } else {
                 ptr::copy_nonoverlapping(preopen.path.ptr, path, preopen.path.len);