ROX-33199: unlink inode tracking

fact-ebpf/src/bpf/main.c

@@ -94,6 +94,9 @@ int BPF_PROG(trace_path_unlink, struct path* dir, struct dentry* dentry) {
     return 0;
   }
 
+  // We only support files with one link for now
+  inode_remove(&inode_key);
+
   submit_unlink_event(&m->path_unlink,
                       path->path,
                       inode_to_submit,

fact/src/event/mod.rs

@@ -130,6 +130,10 @@ impl Event {
         matches!(self.file, FileData::Creation(_))
     }
 
+    pub fn is_unlink(&self) -> bool {
+        matches!(self.file, FileData::Unlink(_))
+    }
+
     /// Unwrap the inner FileData and return the inode that triggered
     /// the event.
     ///

fact/src/host_scanner.rs

@@ -220,6 +220,18 @@ impl HostScanner {
         Ok(())
     }
 
+    /// Special handling for unlink events.
+    ///
+    /// This method removes the inode from the userland inode->path map.
+    /// The probe already cleared the kernel inode map.
+    fn handle_unlink_event(&self, event: &Event) {
+        let inode = event.get_inode();
+
+        if self.inode_map.borrow_mut().remove(inode).is_some() {
+            self.metrics.scan_inc(ScanLabels::InodeRemoved);
+        }
+    }
+
     /// Periodically notify the host scanner main task that a scan needs
     /// to happen.
     ///
@@ -277,6 +289,11 @@ impl HostScanner {
                             event.set_old_host_path(host_path);
                         }
 
+                        // Special handling for unlink events
+                        if event.is_unlink() {
+                            self.handle_unlink_event(&event);
+                        }
+
                         let event = Arc::new(event);
                         if let Err(e) = self.tx.send(event) {
                             self.metrics.events.dropped();

tests/test_path_unlink.py

@@ -227,3 +227,55 @@ def test_unmonitored_mounted_dir(test_container, test_file, server):
                   file=fut, host_path=test_file)
 
     server.wait_events([event])
+
+
+def test_probe_inode_map(monitored_dir, ignored_dir, server):
+    """
+    TODO[ROX-33222]: This test won't work when hardlinks are handled properly.
+
+    This test demonstrates that the current implementation removes the inode
+    from the kernel map correctly, as a second unmonitored hardlink deletion
+    is not noticed.
+
+    Args:
+        monitored_dir: Temporary directory path that is monitored by fact.
+        ignored_dir: Temporary directory path that is NOT monitored by fact.
+        server: The server instance to communicate with.
+    """
+    process = Process.from_proc()
+
+    # File Under Test - original file in monitored directory
+    original_file = os.path.join(monitored_dir, 'original.txt')
+
+    # Create the original file
+    with open(original_file, 'w') as f:
+        f.write('This is a test')
+
+    # Create two hardlinks in the unmonitored directory
+    hardlink_file1 = os.path.join(ignored_dir, 'hardlink1.txt')
+    os.link(original_file, hardlink_file1)
+
+    hardlink_file2 = os.path.join(ignored_dir, 'hardlink2.txt')
+    os.link(original_file, hardlink_file2)
+
+    e = Event(process=process, event_type=EventType.CREATION,
+              file=original_file, host_path=original_file)
+
+    server.wait_events([e])
+
+    os.remove(hardlink_file1)
+    os.remove(hardlink_file2)
+
+    # Create a guard file to ensure all events have been processed
+    guard_file = os.path.join(monitored_dir, 'guard.txt')
+    with open(guard_file, 'w') as f:
+        f.write('guard')
+
+    events = [
+        Event(process=process, event_type=EventType.UNLINK,
+              file=hardlink_file1, host_path=original_file),
+        Event(process=process, event_type=EventType.CREATION,
+              file=guard_file, host_path=guard_file),
+    ]
+
+    server.wait_events(events)