[dpdk-dev] [PATCH v2] Fix `eventfd_link' module leakages and races

[Pavel Boldin <pboldin@mirantis.com>]

The `eventfd_link' module provides an API to "steal" fd from another
process had been written with a bug that leaks `struct file' because
of the extra reference counter increment and missing `fput' call.

The other bug is using another process' `task_struct' without incrementing
a reference counter.

Fix these bugs and refactor the module.
---

Changes since last submission:

* Rebased to the `master' version,
* Corrected error codes returned.

 lib/librte_vhost/eventfd_link/eventfd_link.c | 212 ++++++++++++++++-----------
 1 file changed, 125 insertions(+), 87 deletions(-)

diff --git a/lib/librte_vhost/eventfd_link/eventfd_link.c b/lib/librte_vhost/eventfd_link/eventfd_link.c
index 7755dd6..57b0a8a 100644
--- a/lib/librte_vhost/eventfd_link/eventfd_link.c
+++ b/lib/librte_vhost/eventfd_link/eventfd_link.c
@@ -65,100 +65,138 @@ put_files_struct(struct files_struct *files)
 		BUG();
 }
 
+static struct file *
+fget_from_files(struct files_struct *files, unsigned fd)
+{
+	struct file *file;
 
-static long
-eventfd_link_ioctl(struct file *f, unsigned int ioctl, unsigned long arg)
+	rcu_read_lock();
+	file = fcheck_files(files, fd);
+	if (file)
+	{
+		if (file->f_mode & FMODE_PATH
+			|| !atomic_long_inc_not_zero(&file->f_count))
+		    file = NULL;
+	}
+	rcu_read_unlock();
+
+	return file;
+}
+
+static int
+close_fd(unsigned fd)
 {
-	void __user *argp = (void __user *) arg;
-	struct task_struct *task_target = NULL;
 	struct file *file;
-	struct files_struct *files;
+	struct files_struct *files = current->files;
 	struct fdtable *fdt;
+
+	spin_lock(&files->file_lock);
+	fdt = files_fdtable(files);
+	if (fd >= fdt->max_fds)
+		goto out_unlock;
+	file = fdt->fd[fd];
+	if (!file)
+		goto out_unlock;
+	rcu_assign_pointer(fdt->fd[fd], NULL);
+	__clear_bit(fd, fdt->close_on_exec);
+	spin_unlock(&files->file_lock);
+	return filp_close(file, files);
+
+out_unlock:
+	spin_unlock(&files->file_lock);
+	return -EBADF;
+}
+
+
+static long
+eventfd_link_ioctl_copy(unsigned long arg)
+{
+	long ret = -EFAULT;
+	struct task_struct *task_target = NULL;
+	struct file *target_file = NULL;
+	struct files_struct *target_files = NULL;
 	struct eventfd_copy eventfd_copy;
+	struct pid *pid;
+
+	if (copy_from_user(&eventfd_copy, (void __user*)arg,
+			    sizeof(struct eventfd_copy)))
+		goto out;
+
+	/*
+	 * Find the task struct for the target pid
+	 */
+	ret = -ESRCH;
+
+	pid = find_vpid(eventfd_copy.target_pid);
+	if (pid == NULL) {
+		pr_info("Unable to find pid %d\n", eventfd_copy.target_pid);
+		goto out;
+	}
+
+	task_target = get_pid_task(pid, PIDTYPE_PID);
+	if (task_target == NULL) {
+		pr_info("Failed to get task for pid %d\n",
+			eventfd_copy.target_pid);
+		goto out;
+	}
+
+	ret = close_fd(eventfd_copy.source_fd);
+	if (ret)
+		goto out_task;
+	ret = -ESTALE;
+
+	/*
+	 * Find the file struct associated with the target fd.
+	 */
+
+	target_files = get_files_struct(task_target);
+	if (target_files == NULL) {
+		pr_info("Failed to get target files struct\n");
+		goto out_task;
+	}
+
+	ret = -EBADF;
+	target_file = fget_from_files(target_files, eventfd_copy.target_fd);
+
+	if (target_file == NULL) {
+		pr_info("Failed to get file from target pid\n");
+		goto out_target_files;
+	}
 
-	switch (ioctl) {
-	case EVENTFD_COPY:
-		if (copy_from_user(&eventfd_copy, argp,
-			sizeof(struct eventfd_copy)))
-			return -EFAULT;
-
-		/*
-		 * Find the task struct for the target pid
-		 */
-		task_target =
-			pid_task(find_vpid(eventfd_copy.target_pid), PIDTYPE_PID);
-		if (task_target == NULL) {
-			pr_debug("Failed to get mem ctx for target pid\n");
-			return -EFAULT;
-		}
-
-		files = get_files_struct(current);
-		if (files == NULL) {
-			pr_debug("Failed to get files struct\n");
-			return -EFAULT;
-		}
-
-		rcu_read_lock();
-		file = fcheck_files(files, eventfd_copy.source_fd);
-		if (file) {
-			if (file->f_mode & FMODE_PATH ||
-				!atomic_long_inc_not_zero(&file->f_count))
-				file = NULL;
-		}
-		rcu_read_unlock();
-		put_files_struct(files);
-
-		if (file == NULL) {
-			pr_debug("Failed to get file from source pid\n");
-			return 0;
-		}
-
-		/*
-		 * Release the existing eventfd in the source process
-		 */
-		spin_lock(&files->file_lock);
-		filp_close(file, files);
-		fdt = files_fdtable(files);
-		fdt->fd[eventfd_copy.source_fd] = NULL;
-		spin_unlock(&files->file_lock);
-
-		/*
-		 * Find the file struct associated with the target fd.
-		 */
-
-		files = get_files_struct(task_target);
-		if (files == NULL) {
-			pr_debug("Failed to get files struct\n");
-			return -EFAULT;
-		}
-
-		rcu_read_lock();
-		file = fcheck_files(files, eventfd_copy.target_fd);
-		if (file) {
-			if (file->f_mode & FMODE_PATH ||
-				!atomic_long_inc_not_zero(&file->f_count))
-					file = NULL;
-		}
-		rcu_read_unlock();
-		put_files_struct(files);
-
-		if (file == NULL) {
-			pr_debug("Failed to get file from target pid\n");
-			return 0;
-		}
-
-		/*
-		 * Install the file struct from the target process into the
-		 * file desciptor of the source process,
-		 */
-
-		fd_install(eventfd_copy.source_fd, file);
-
-		return 0;
-
-	default:
-		return -ENOIOCTLCMD;
+
+	/*
+	 * Install the file struct from the target process into the
+	 * file desciptor of the source process,
+	 */
+
+	fd_install(eventfd_copy.source_fd, target_file);
+
+	ret = 0;
+
+out_target_files:
+	put_files_struct(target_files);
+out_task:
+	put_task_struct(task_target);
+out:
+	return ret;
+}
+
+static long
+eventfd_link_ioctl(struct file *f, unsigned int ioctl, unsigned long arg)
+{
+	long ret;
+
+	switch (ioctl)
+	{
+		case EVENTFD_COPY:
+			ret = eventfd_link_ioctl_copy(arg);
+			break;
+		default:
+			ret = -ENOIOCTLCMD;
+			break;
 	}
+
+	return ret;
 }
 
 static const struct file_operations eventfd_link_fops = {
-- 
1.9.1