linux-kernel - [PATCH v2 11/24] file: Implement task_lookup_fd

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Message-Id: <20201120231441.29911-11-ebiederm@xmission.com>
Date:   Fri, 20 Nov 2020 17:14:28 -0600
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@...radead.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        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 v2 11/24] file: Implement task_lookup_fd_rcu

As a companion to lookup_fd_rcu implement task_lookup_fd_rcu for
querying an arbitrary process about a specific file.

Acked-by: Christian Brauner <christian.brauner@...ntu.com>
v1: https://lkml.kernel.org/r/20200818103713.aw46m7vprsy4vlve@wittgenstein
Signed-off-by: "Eric W. Biederman" <ebiederm@...ssion.com>
---
 fs/file.c               | 15 +++++++++++++++
 include/linux/fdtable.h |  2 ++
 2 files changed, 17 insertions(+)

diff --git a/fs/file.c b/fs/file.c
index 5861c4f89419..6448523ca29e 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -865,6 +865,21 @@ struct file *fget_task(struct task_struct *task, unsigned int fd)
 	return file;
 }
 
+struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd)
+{
+	/* Must be called with rcu_read_lock held */
+	struct files_struct *files;
+	struct file *file = NULL;
+
+	task_lock(task);
+	files = task->files;
+	if (files)
+		file = files_lookup_fd_rcu(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 2a4a8fed536e..a0558ae9b40c 100644
--- a/include/linux/fdtable.h
+++ b/include/linux/fdtable.h
@@ -110,6 +110,8 @@ static inline struct file *lookup_fd_rcu(unsigned int fd)
 	return files_lookup_fd_rcu(current->files, fd);
 }
 
+struct file *task_lookup_fd_rcu(struct task_struct *task, unsigned int fd);
+
 struct task_struct;
 
 struct files_struct *get_files_struct(struct task_struct *);
-- 
2.25.0