Re: [RFC PATCH] ptrace: add PTRACE_GETFD request

On Thu, Dec 05, 2019 at 11:44:53PM +0000, Sargun Dhillon wrote:

quoted

+static int ptrace_getfd(struct task_struct *child, unsigned long fd)
+{
+	struct files_struct *files;
+	struct file *file;
+	int ret = 0;
+
+	files = get_files_struct(child);
+	if (!files)
+		return -ENOENT;
+
+	spin_lock(&files->file_lock);
+	file = fcheck_files(files, fd);
+	if (!file)
+		ret = -EBADF;
+	else
+		get_file(file);
+	spin_unlock(&files->file_lock);
+	put_files_struct(files);

may be someone can finally create a helper for this, it can have more users.
say,
	struct file *get_task_file(task, fd)
	{
		struct file *file = NULL;

		task_lock(task);
		rcu_read_lock();
		if (task->files) {
			file = fcheck_files(task->files, fd);
			if (file)
				get_file(file);
		}
		rcu_read_unlock();
		task_unlock(task);

		return file;
	}


no need to get/put files_struct, no need to take ->file_lock.

quoted

+
+	if (ret)
+		goto out;
+
+	ret = get_unused_fd_flags(0);
+	if (ret >= 0)
+		fd_install(ret, file);
+
+	fput(file);

this looks wrong or I am totally confused...

	if (ret >= 0)
		fd_install(file);
	else
		fput(file);

?

quoted

@@ -1265,7 +1299,8 @@ SYSCALL_DEFINE4(ptrace, long, request, long, pid, unsigned long, addr,
 	}
 
 	ret = ptrace_check_attach(child, request == PTRACE_KILL ||
-				  request == PTRACE_INTERRUPT);
+				  request == PTRACE_INTERRUPT ||
+				  request == PTRACE_GETFD);

Hmm. not sure why do you want this... But OK, we do not need to stop the tracee.

Oleg.