linux-kernel - Re: [PATCH RFC v2 5/6] proc: instantiate only pids that we can ptrace on 'limit

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Date:   Wed, 26 Apr 2017 15:09:09 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Djalal Harouni <tixxdz@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Dongsu Park <dpark@...teo.net>,
        Casey Schaufler <casey@...aufler-ca.com>,
        James Morris <james.l.morris@...cle.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Jeff Layton <jlayton@...chiereds.net>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Ingo Molnar <mingo@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>,
        Michal Hocko <mhocko@...e.com>,
        Jonathan Corbet <corbet@....net>
Subject: Re: [PATCH RFC v2 5/6] proc: instantiate only pids that we can ptrace
 on 'limit_pids=1' mount option

On Tue, Apr 25, 2017 at 5:23 AM, Djalal Harouni <tixxdz@...il.com> wrote:
> If "limit_pids=1" mount option is set then do not instantiate pids that
> we can not ptrace. "limit_pids=1" means that procfs should only contain
> pids that the caller can ptrace.
>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Andy Lutomirski <luto@...nel.org>
> Signed-off-by: Djalal Harouni <tixxdz@...il.com>
> ---
>  fs/proc/base.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 2e0f661..a663284 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -3149,6 +3149,7 @@ struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, unsign
>         unsigned tgid;
>         struct proc_fs_info *fs_info = proc_sb(dir->i_sb);
>         struct pid_namespace *ns = fs_info->pid_ns;
> +       int limit_pids = proc_fs_limit_pids(fs_info);

Shouldn't the addition of proc_fs_limit_pids() be in this patch?

Also, can we name it something self-documented?
"ptraceable_pids_only=1", perhaps?  Or even pids=ptraceable (as
opposed to pids=all or maybe other choices in the future)?

--Andy