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Date: Wed, 8 Jan 2020 11:37:41 +0100
From: Alexey Gladkov <gladkov.alexey@...il.com>
To: Alexey Dobriyan <adobriyan@...il.com>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Kernel Hardening <kernel-hardening@...ts.openwall.com>,
	Linux API <linux-api@...r.kernel.org>,
	Linux FS Devel <linux-fsdevel@...r.kernel.org>,
	Linux Security Module <linux-security-module@...r.kernel.org>,
	Akinobu Mita <akinobu.mita@...il.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Daniel Micay <danielmicay@...il.com>,
	Djalal Harouni <tixxdz@...il.com>,
	"Dmitry V . Levin" <ldv@...linux.org>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	"J . Bruce Fields" <bfields@...ldses.org>,
	Jeff Layton <jlayton@...chiereds.net>,
	Jonathan Corbet <corbet@....net>, Kees Cook <keescook@...omium.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Solar Designer <solar@...nwall.com>
Subject: Re: [PATCH v6 00/10] proc: modernize proc to support multiple
 private instances

On Mon, Jan 06, 2020 at 06:15:14PM +0300, Alexey Dobriyan wrote:
> >  	hidepid=	Set /proc/<pid>/ access mode.
> >  	gid=		Set the group authorized to learn processes information.
> > +	pidonly=	Show only task related subset of procfs.
> 
> I'd rather have
> 
> 	mount -t proc -o set=pid

This is a great idea.

> so that is can be naturally extended to 
> 
> 	mount -t proc -o set=pid,sysctl,misc
>
> > +static int proc_dir_open(struct inode *inode, struct file *file)
> > +{
> > +	struct proc_fs_info *fs_info = proc_sb_info(inode->i_sb);
> > +
> > +	if (proc_fs_pidonly(fs_info) == PROC_PIDONLY_ON)
> > +		return -ENOENT;
> > +
> > +	return 0;
> > +}
> > +
> >  /*
> >   * These are the generic /proc directory operations. They
> >   * use the in-memory "struct proc_dir_entry" tree to parse
> > @@ -338,6 +357,7 @@ static const struct file_operations proc_dir_operations = {
> >  	.llseek			= generic_file_llseek,
> >  	.read			= generic_read_dir,
> >  	.iterate_shared		= proc_readdir,
> > +	.open			= proc_dir_open,
> 
> This should not be necessary: if lookup and readdir filters work
> then ->open can't happen.

Yes you are right.

> > --- a/include/linux/proc_fs.h
> > +++ b/include/linux/proc_fs.h
> > +/* definitions for hide_pid field */
> > +enum {
> > +	HIDEPID_OFF	  = 0,
> > +	HIDEPID_NO_ACCESS = 1,
> > +	HIDEPID_INVISIBLE = 2,
> > +	HIDEPID_NOT_PTRACABLE = 3, /* Limit pids to only ptracable pids */
> > +};
> 
> These should live in uapi/ as they _are_ user interface to mount().

OK.

What do you think, maybe it's better to make these values a mask ?

I mean:

#define HIDEPID_OFF 0
#define HIDEPID_NO_ACCESS 1
#define HIDEPID_INVISIBLE 2
#define HIDEPID_NOT_PTRACABLE 4

In this case, if in the future there appear values that can be combined,
then there will be no need to make additional parameters.

-- 
Rgrds, legion

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