linux-kernel - Re: [PATCH v5 5/7] proc: instantiate only pids that we can ptrace on 'limit

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Message-ID: <20180514082908.GA28179@comp-core-i7-2640m-0182e6>
Date:   Mon, 14 May 2018 10:29:08 +0200
From:   Alexey Gladkov <gladkov.alexey@...il.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Andrew Lutomirski <luto@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Kernel Hardening <kernel-hardening@...ts.openwall.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Akinobu Mita <akinobu.mita@...il.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        Ingo Molnar <mingo@...nel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Daniel Micay <danielmicay@...il.com>,
        Jonathan Corbet <corbet@....net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Solar Designer <solar@...nwall.com>,
        "Dmitry V. Levin" <ldv@...linux.org>,
        Djalal Harouni <tixxdz@...il.com>
Subject: Re: [PATCH v5 5/7] proc: instantiate only pids that we can ptrace on
 'limit_pids=1' mount option

On Fri, May 11, 2018 at 09:45:33AM -0700, Linus Torvalds wrote:
> On Fri, May 11, 2018 at 2:46 AM Alexey Gladkov <gladkov.alexey@...il.com>
> wrote:
> 
> > +       /* Limit procfs to only ptracable tasks */
> > +       if (limit_pids == PROC_LIMIT_PIDS_PTRACE) {
> > +               cond_resched();
> > +               if (!has_pid_permissions(fs_info, task,
> HIDEPID_NO_ACCESS))
> > +                       goto out_put_task;
> > +       }
> 
> Where did that "cond_resched()" come from? That doesn't seem to make a lot
> of sense.

This call came along with has_pid_permissions from proc_pid_readdir [1]. It
seems to me that proc_pid_readdir and proc_pid_lookup should act in a
similar way in this case.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3ba4bceef23206349d4130ddf140819b365de7c8

-- 
Rgrds, legion