[CRIU] [PATCH 06/17] file: Implement fcheck_task

[Hillf Danton]

On Mon, 17 Aug 2020 17:04:14 -0500
> As a companion to fget_task implement fcheck_task for use for querying
> a process about a specific file.
> 
> Signed-off-by: "Eric W. Biederman" <ebiederm at xmission.com>
> ---
>  fs/file.c               | 13 +++++++++++++
>  include/linux/fdtable.h |  1 +
>  2 files changed, 14 insertions(+)
> 
> diff --git a/fs/file.c b/fs/file.c
> index c585dbaf31a3..8d4b385055e9 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -863,6 +863,19 @@ struct file *fget_task(struct task_struct *task, unsigned int fd)
>  	return file;
>  }
>  
> +struct file *fcheck_task(struct task_struct *task, unsigned int fd)
> +{
> +	/* Must be called with rcu_read_lock held */
> +	struct file *file = NULL;

It seems something like lockdep_assert_rcu_read_lock() can do
more for syzbot than a-line comment would.

> +
> +	task_lock(task);
> +	if (task->files)
> +		file = fcheck_files(task->files, fd);
> +	task_unlock(task);
> +
> +	return file;
> +}
> +
>  /*
>   * Lightweight file lookup - no refcnt increment if fd table isn't shared.
>   *
> diff --git a/include/linux/fdtable.h b/include/linux/fdtable.h
> index 7cc9885044d9..def9debd2ce2 100644
> --- a/include/linux/fdtable.h
> +++ b/include/linux/fdtable.h
> @@ -103,6 +103,7 @@ static inline struct file *fcheck_files(struct files_struct *files, unsigned int
>   * Check whether the specified fd has an open file.
>   */
>  #define fcheck(fd)	fcheck_files(current->files, fd)
> +struct file *fcheck_task(struct task_struct *task, unsigned int fd);
>  
>  struct task_struct;
>  
> -- 
> 2.25.0