From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Brauner Subject: [PATCH v1 1/2] proc: get process file descriptor from /proc/ Date: Mon, 19 Nov 2018 11:32:38 +0100 Message-ID: <20181119103241.5229-2-christian@brauner.io> References: <20181119103241.5229-1-christian@brauner.io> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20181119103241.5229-1-christian@brauner.io> Sender: linux-kernel-owner@vger.kernel.org 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 , Kees Cook List-Id: linux-api@vger.kernel.org With this patch an open() call on /proc/ will give userspace a handle to struct pid of the process associated with /proc/. 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" Cc: Serge Hallyn Cc: Jann Horn Cc: Kees Cook Cc: Andy Lutomirsky Cc: Andrew Morton Cc: Oleg Nesterov Cc: Aleksa Sarai Cc: Al Viro Signed-off-by: Christian Brauner --- 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