linux-kernel - Re: [RFC PATCH] ptrace: add PTRACE

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Date:   Fri, 6 Dec 2019 20:05:59 +0100
From:   Jann Horn <jannh@...gle.com>
To:     Sargun Dhillon <sargun@...gun.me>
Cc:     Tycho Andersen <tycho@...ho.ws>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Containers <containers@...ts.linux-foundation.org>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: [RFC PATCH] ptrace: add PTRACE_GETFD request

On Fri, Dec 6, 2019 at 8:05 PM Jann Horn <jannh@...gle.com> wrote:
> On Fri, Dec 6, 2019 at 8:03 PM Sargun Dhillon <sargun@...gun.me> wrote:
> > On Fri, Dec 6, 2019 at 6:10 AM Tycho Andersen <tycho@...ho.ws> wrote:
> > > On Thu, Dec 05, 2019 at 11:44:53PM +0000, Sargun Dhillon wrote:
> > > > take action on an FD on behalf of the tracee. For example, this
> > > > can be combined with seccomp's user notification feature to extract
> > > > a file descriptor and call privileged syscalls, like binding
> > > > a socket to a privileged port.
> > >
> > > This can already be accomplished via injecting parasite code like CRIU
> > > does; adding a ptrace() command like this makes it much nicer to be
> > > sure, but it is redundant.
> > >
> > How can you do this if the tracee doesn't have privilege? For example,
> > if the tracee doesn't have CAP_SYS_BIND_SERVICE, how could you
> > get it to bind to a port that's privileged without taking the file descriptor
> > and doing it in a process that does have CAP_SYS_BIND_SERVICE?
>
> (You can let the parasite send the fd to the tracer via
> SCM_CREDENTIALS if you have previously set up a unix domain socket for
> this.)

Eh, sorry, of course I meant SCM_RIGHTS.