linux-kernel - Re: [PATCH v6 3/5] seccomp: add a way to get a listener fd from ptrace

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Thu, 6 Sep 2018 09:50:08 -0600
From:   Tycho Andersen <tycho@...ho.ws>
To:     Jann Horn <jannh@...gle.com>
Cc:     Kees Cook <keescook@...omium.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        containers@...ts.linux-foundation.org,
        Linux API <linux-api@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>,
        Oleg Nesterov <oleg@...hat.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Tyler Hicks <tyhicks@...onical.com>, suda.akihiro@....ntt.co.jp
Subject: Re: [PATCH v6 3/5] seccomp: add a way to get a listener fd from
 ptrace

On Thu, Sep 06, 2018 at 05:45:25PM +0200, Jann Horn wrote:
> On Thu, Sep 6, 2018 at 5:29 PM Tycho Andersen <tycho@...ho.ws> wrote:
> >
> > As an alternative to SECCOMP_FILTER_FLAG_GET_LISTENER, perhaps a ptrace()
> > version which can acquire filters is useful. There are at least two reasons
> > this is preferable, even though it uses ptrace:
> >
> > 1. You can control tasks that aren't cooperating with you
> > 2. You can control tasks whose filters block sendmsg() and socket(); if the
> >    task installs a filter which blocks these calls, there's no way with
> >    SECCOMP_FILTER_FLAG_GET_LISTENER to get the fd out to the privileged task.
> [...]
> > +long seccomp_new_listener(struct task_struct *task,
> > +                         unsigned long filter_off)
> > +{
> > +       struct seccomp_filter *filter;
> > +       struct file *listener;
> > +       int fd;
> > +
> > +       if (!capable(CAP_SYS_ADMIN))
> > +               return -EACCES;
> > +
> > +       filter = get_nth_filter(task, filter_off);
> > +       if (IS_ERR(filter))
> > +               return PTR_ERR(filter);
> > +
> > +       fd = get_unused_fd_flags(0);
> > +       if (fd < 0) {
> > +               __put_seccomp_filter(filter);
> > +               return fd;
> > +       }
> > +
> > +       listener = init_listener(task, task->seccomp.filter);
> 
> Did you mean to write something like `init_listener(task, filter)` here?

Yes, yes I did. Thanks, Jann.

Tycho