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

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Mar 16, 2015 at 06:40:59PM +0200, Pavel Boldin wrote:
> From: 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.
> ---
>  examples/vhost/eventfd_link/eventfd_link.c | 236 ++++++++++++++++-------------
>  1 file changed, 130 insertions(+), 106 deletions(-)
> 
> diff --git a/examples/vhost/eventfd_link/eventfd_link.c b/examples/vhost/eventfd_link/eventfd_link.c
> index 69470ba..9f1f8fb 100644
> --- a/examples/vhost/eventfd_link/eventfd_link.c
> +++ b/examples/vhost/eventfd_link/eventfd_link.c
> @@ -42,15 +42,15 @@
>   * get_files_struct is copied from fs/file.c
>   */
>  struct files_struct *
> -get_files_struct (struct task_struct *task)
> +get_files_struct(struct task_struct *task)
>  {
>  	struct files_struct *files;
>  
> -	task_lock (task);
> +	task_lock(task);
>  	files = task->files;
>  	if (files)
> -		atomic_inc (&files->count);
> -	task_unlock (task);
> +		atomic_inc(&files->count);
> +	task_unlock(task);
>  
>  	return files;
>  }
> @@ -59,117 +59,142 @@ get_files_struct (struct task_struct *task)
>   * put_files_struct is extracted from fs/file.c
>   */
>  void
> -put_files_struct (struct files_struct *files)
> +put_files_struct(struct files_struct *files)
>  {
> -	if (atomic_dec_and_test (&files->count))
> -	{
> +	if (atomic_dec_and_test(&files->count))
>  		BUG ();
> +}
> +
> +static struct file *
> +fget_from_files(struct files_struct *files, unsigned fd)
> +{
> +	struct file *file;
> +
> +	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)
> +{
> +	struct file *file;
> +	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 (struct file *f, unsigned int ioctl, unsigned long arg)
> +eventfd_link_ioctl_copy(unsigned long arg)
>  {
> -	void __user *argp = (void __user *) arg;
> +	long ret = -EFAULT;
>  	struct task_struct *task_target = NULL;
> -	struct file *file;
> -	struct files_struct *files;
> -	struct fdtable *fdt;
> +	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
> +	 */
> +	pid = find_vpid(eventfd_copy.target_pid);
> +	if (pid == NULL) {
> +		printk(KERN_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) {
> +		printk(KERN_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 = -EFAULT;
> +
> +	/*
> +	 * Find the file struct associated with the target fd.
> +	 */
> +
> +	target_files = get_files_struct(task_target);
> +	if (target_files == NULL) {
> +		printk (KERN_INFO "Failed to get target files struct\n");
> +		goto out_task;
> +	}
> +
> +	target_file = fget_from_files(target_files, eventfd_copy.target_fd);
> +
> +	if (target_file == NULL) {
> +		printk (KERN_INFO "Failed to get file from target pid\n");
> +		goto out_target_files;
> +	}
> +
> +
> +	/*
> +	 * 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:
> -			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)
> -			{
> -				printk (KERN_DEBUG "Failed to get mem ctx for target pid\n");
> -				return -EFAULT;
> -			}
> -
> -			files = get_files_struct (current);
> -			if (files == NULL)
> -			{
> -				printk (KERN_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)
> -			{
> -				printk (KERN_DEBUG "Failed to get file from source pid\n");
> -				return 0;
> -			}
> -
> -			/*
> -			 * Release the existing eventfd in the source process
> -			 */
> -			spin_lock (&files->file_lock);
> -			fput(file);
> -			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)
> -			{
> -				printk (KERN_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)
> -			{
> -				printk (KERN_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;
> -
> +			ret = eventfd_link_ioctl_copy(arg);
> +			break;
>  		default:
> -			return -ENOIOCTLCMD;
> +			ret = -ENOIOCTLCMD;
> +			break;
>  	}
> +
> +	return ret;
>  }
>  
>  static const struct file_operations eventfd_link_fops = {
> @@ -184,21 +209,20 @@ static struct miscdevice eventfd_link_misc = {
>  };
>  
>  static int __init
> -eventfd_link_init (void)
> +eventfd_link_init(void)
>  {
> -	printk(KERN_INFO "eventfd_link is broken, use it at your risk\n");
> -	return misc_register (&eventfd_link_misc);
> +	return misc_register(&eventfd_link_misc);
>  }
>  
> -module_init (eventfd_link_init);
> +module_init(eventfd_link_init);
>  
>  static void __exit
> -eventfd_link_exit (void)
> +eventfd_link_exit(void)
>  {
> -	misc_deregister (&eventfd_link_misc);
> +	misc_deregister(&eventfd_link_misc);
>  }
>  
> -module_exit (eventfd_link_exit);
> +module_exit(eventfd_link_exit);
>  
>  MODULE_VERSION ("0.0.1");
>  MODULE_LICENSE ("GPL v2");
> -- 
> 1.9.1
> 
> 
You need to respin this.  This library has since moved to another location in
the tree
Neil