[06/17] file: Implement fcheck_task

Submitted by Eric W. Biederman on Aug. 17, 2020, 10:04 p.m.

Details

Message ID 20200817220425.9389-6-ebiederm@xmission.com
State New
Series "Series without cover letter"
Headers show

Commit Message

Eric W. Biederman Aug. 17, 2020, 10:04 p.m.
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@xmission.com>
---
 fs/file.c               | 13 +++++++++++++
 include/linux/fdtable.h |  1 +
 2 files changed, 14 insertions(+)

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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;
+
+	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;
 

Comments

Hillf Danton Aug. 18, 2020, 2:09 a.m.
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@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
Christian Brauner Aug. 18, 2020, 10:37 a.m.
On Mon, Aug 17, 2020 at 05:04:14PM -0500, Eric W. Biederman wrote:
> 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@xmission.com>
> ---

Acked-by: Christian Brauner <christian.brauner@ubuntu.com>