linux-kernel - [PATCH 06/17] file: Implement fcheck

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Date:   Mon, 17 Aug 2020 17:04:14 -0500
From:   "Eric W. Biederman" <ebiederm@...ssion.com>
To:     linux-kernel@...r.kernel.org
Cc:     linux-fsdevel@...r.kernel.org, criu@...nvz.org,
        bpf@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Jann Horn <jann@...jh.net>, Kees Cook <keescook@...omium.org>,
        Daniel P. Berrangé <berrange@...hat.com>,
        Jeff Layton <jlayton@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Matthew Wilcox <willy@...ian.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Matthew Wilcox <matthew@....cx>,
        Trond Myklebust <trond.myklebust@....uio.no>,
        Chris Wright <chrisw@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>
Subject: [PATCH 06/17] file: Implement fcheck_task

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@...ssion.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;
+
+	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