fix(clipboard): unix, check file transfer permission on incoming file… (#16333)

* fix(clipboard): unix, check file transfer permission on incoming file clipboard

The Cliprdr arm served incoming file clipboard messages on Linux/macOS
without checking the file transfer permission, which the controlled
side can turn off mid-session. can_sub_file_clipboard_service() only
gates the outgoing service, so a peer could keep pushing files in and
keep requesting the host's copied file list and contents.

Check file_transfer_enabled() on every message. It is the same
permission the client and the Windows cm use for file copy-paste.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* fix(clipboard): honor one-way file transfer on incoming file requests

One-way file transfer was only enforced on the outgoing side: the host
never announces its clipboard files. A controller could still send
FormatDataRequest / FileContentsRequest directly, and the host answered
them, from the live clipboard on Windows and from serv_files on
Linux/macOS.

Drop those two requests when one-way file transfer is on, before any
platform handling. The messages that carry the peer's own files to
this side are untouched.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

* style: drop redundant doc comment

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/clipboard_file.rs

@@ -224,6 +224,13 @@ pub fn msg_2_clip(msg: Cliprdr) -> Option<ClipboardFile> {
     }
 }
 
+pub fn is_file_data_request(msg: &Cliprdr) -> bool {
+    matches!(
+        msg.union,
+        Some(cliprdr::Union::FormatDataRequest(_)) | Some(cliprdr::Union::FileContentsRequest(_))
+    )
+}
+
 #[cfg(feature = "unix-file-copy-paste")]
 pub mod unix_file_clip {
     use super::*;
@@ -433,3 +440,52 @@ pub mod unix_file_clip {
         vec![]
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn is_request(clip: ClipboardFile) -> bool {
+        match clip_2_msg(clip).union {
+            Some(message::Union::Cliprdr(msg)) => is_file_data_request(&msg),
+            _ => false,
+        }
+    }
+
+    #[test]
+    fn test_is_file_data_request() {
+        assert!(is_request(ClipboardFile::FormatDataRequest {
+            requested_format_id: 0,
+        }));
+        assert!(is_request(ClipboardFile::FileContentsRequest {
+            stream_id: 0,
+            list_index: 0,
+            dw_flags: 0,
+            n_position_low: 0,
+            n_position_high: 0,
+            cb_requested: 0,
+            have_clip_data_id: false,
+            clip_data_id: 0,
+        }));
+
+        // Messages that carry the peer's own clipboard files must stay allowed.
+        assert!(!is_request(ClipboardFile::MonitorReady));
+        assert!(!is_request(ClipboardFile::FormatList {
+            format_list: vec![],
+        }));
+        assert!(!is_request(ClipboardFile::FormatListResponse {
+            msg_flags: 0
+        }));
+        assert!(!is_request(ClipboardFile::FormatDataResponse {
+            msg_flags: 0,
+            format_data: vec![],
+        }));
+        assert!(!is_request(ClipboardFile::FileContentsResponse {
+            msg_flags: 0,
+            stream_id: 0,
+            requested_data: vec![],
+        }));
+        assert!(!is_request(ClipboardFile::TryEmpty));
+        assert!(!is_request(ClipboardFile::Files { files: vec![] }));
+    }
+}

src/server/connection.rs

@@ -3387,13 +3387,19 @@ impl Connection {
                                 .collect::<Vec<(String, i64)>>(),
                             json!({}),
                         );
+                    } else if is_file_data_request(&clip)
+                        && crate::get_builtin_option(keys::OPTION_ONE_WAY_FILE_TRANSFER) == "Y"
+                    {
+                        // One-way file transfer: never serve this side's clipboard files to the peer.
                     } else if let Some(clip) = msg_2_clip(clip) {
                         #[cfg(target_os = "windows")]
                         {
                             self.send_to_cm(ipc::Data::ClipboardFile(clip));
                         }
                         #[cfg(feature = "unix-file-copy-paste")]
-                        if crate::is_support_file_copy_paste(&self.lr.version) {
+                        if crate::is_support_file_copy_paste(&self.lr.version)
+                            && self.file_transfer_enabled()
+                        {
                             let mut out_msgs = vec![];
 
                             #[cfg(target_os = "macos")]