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From: Christian Brauner <christian@brauner.io>
To: ebiederm@xmission.com, linux-kernel@vger.kernel.org
Cc: serge@hallyn.com, jannh@google.com, luto@kernel.org,
	akpm@linux-foundation.org, oleg@redhat.com, cyphar@cyphar.com,
	viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org,
	linux-api@vger.kernel.org, dancol@google.com,
	timmurray@google.com, linux-man@vger.kernel.org,
	Christian Brauner <christian@brauner.io>,
	Kees Cook <keescook@chromium.org>
Subject: [PATCH v1 1/2] proc: get process file descriptor from /proc/<pid>
Date: Mon, 19 Nov 2018 11:32:38 +0100
Message-ID: <20181119103241.5229-2-christian@brauner.io> (raw)
In-Reply-To: <20181119103241.5229-1-christian@brauner.io>

With this patch an open() call on /proc/<pid> will give userspace a handle
to struct pid of the process associated with /proc/<pid>. This allows to
maintain a stable handle on a process.
I have been discussing various approaches extensively during technical
conferences this year culminating in a long argument with Eric at Linux
Plumbers. The general consensus was that having a handle on a process
should be something that is very simple and easy to maintain with the
option of being extensible via a more advanced api if the need arises. I
believe that this patch is the most simple, dumb, and therefore
maintainable solution.

[1]: https://lkml.org/lkml/2018/10/30/118

Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Serge Hallyn <serge@hallyn.com>
Cc: Jann Horn <jannh@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Andy Lutomirsky <luto@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Christian Brauner <christian@brauner.io>
---
Changelog:
v1:
- remove ioctl() to signal processes and replace with a dedicated syscall
  in the next patch
---
 fs/proc/base.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ce3465479447..6365a4fea314 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3032,10 +3032,27 @@ static int proc_tgid_base_readdir(struct file *file, struct dir_context *ctx)
 				   tgid_base_stuff, ARRAY_SIZE(tgid_base_stuff));
 }
 
+static int proc_tgid_open(struct inode *inode, struct file *file)
+{
+	/* grab reference to struct pid and stash the pointer away */
+	file->private_data = get_pid(proc_pid(inode));
+	return 0;
+}
+
+static int proc_tgid_release(struct inode *inode, struct file *file)
+{
+	struct pid *pid = file->private_data;
+	/* drop reference to struct pid */
+	put_pid(pid);
+	return 0;
+}
+
 static const struct file_operations proc_tgid_base_operations = {
+	.open		= proc_tgid_open,
 	.read		= generic_read_dir,
 	.iterate_shared	= proc_tgid_base_readdir,
 	.llseek		= generic_file_llseek,
+	.release	= proc_tgid_release,
 };
 
 static struct dentry *proc_tgid_base_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
-- 
2.19.1


  reply index

Thread overview: 50+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 10:32 [PATCH v1 0/2] proc: allow signaling processes via file descriptors Christian Brauner
2018-11-19 10:32 ` Christian Brauner [this message]
2018-11-19 15:32   ` [PATCH v1 1/2] proc: get process file descriptor from /proc/<pid> Andy Lutomirski
2018-11-19 18:20     ` Christian Brauner
2018-11-19 10:32 ` [PATCH v1 2/2] signal: add procfd_signal() syscall Christian Brauner
2018-11-19 15:45   ` Andy Lutomirski
2018-11-19 15:57     ` Daniel Colascione
2018-11-19 18:39     ` Christian Brauner
2018-11-19 15:59   ` Daniel Colascione
2018-11-19 18:29     ` Christian Brauner
2018-11-19 19:02       ` Eric W. Biederman
2018-11-19 19:31         ` Christian Brauner
2018-11-19 19:39           ` Daniel Colascione
2018-11-19 17:10   ` Eugene Syromiatnikov
2018-11-19 18:23     ` Christian Brauner
2018-11-19 17:14   ` Eugene Syromiatnikov
2018-11-19 20:28   ` Aleksa Sarai
2018-11-19 20:55     ` Christian Brauner
2018-11-19 21:13       ` Christian Brauner
2018-11-19 21:18       ` Aleksa Sarai
2018-11-19 21:20         ` Christian Brauner
2018-11-19 21:21         ` Christian Brauner
2018-11-19 21:25           ` Aleksa Sarai
2018-11-19 21:26           ` Daniel Colascione
2018-11-19 21:36             ` Aleksa Sarai
2018-11-19 21:37             ` Christian Brauner
2018-11-19 21:41               ` Daniel Colascione
2018-11-20  4:59                 ` Eric W. Biederman
2018-11-20 10:31                   ` Christian Brauner
2018-11-21 21:39                     ` Serge E. Hallyn
2018-11-19 21:23         ` Aleksa Sarai
2018-11-22  7:41           ` Serge E. Hallyn
2018-11-19 22:39   ` Tycho Andersen
2018-11-19 22:49     ` Daniel Colascione
2018-11-19 23:07       ` Tycho Andersen
2018-11-20  0:27         ` Andy Lutomirski
2018-11-20  0:32           ` Christian Brauner
2018-11-20  0:34             ` Andy Lutomirski
2018-11-20  0:49           ` Daniel Colascione
2018-11-22  7:48     ` Serge E. Hallyn
2018-11-19 23:35   ` kbuild test robot
2018-11-19 23:37   ` kbuild test robot
2018-11-19 23:45     ` Christian Brauner
2018-11-28 21:45   ` Joey Pabalinas
2018-11-28 22:05     ` Christian Brauner
2018-11-28 23:02       ` Joey Pabalinas
2018-11-19 10:32 ` [PATCH] procfd_signal.2: document procfd_signal syscall Christian Brauner
2018-11-20 13:29   ` Michael Kerrisk (man-pages)
2018-11-28 20:59   ` Florian Weimer
2018-11-28 21:12     ` Christian Brauner

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