linux-kernel - Re: pidfd design

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]

Message-ID: <CALCETrV-52TXKbAim06Fr7vvFeOvk0SczneeV_Rtqr6-LN7-GQ@mail.gmail.com>
Date:   Mon, 25 Mar 2019 16:42:14 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     Daniel Colascione <dancol@...gle.com>
Cc:     Jann Horn <jannh@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        Christian Brauner <christian@...uner.io>,
        Joel Fernandes <joel@...lfernandes.org>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sultan Alsawaf <sultan@...neltoast.com>,
        Tim Murray <timmurray@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        kernel-team <kernel-team@...roid.com>,
        Oleg Nesterov <oleg@...hat.com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Kees Cook <keescook@...omium.org>,
        Jonathan Kowalski <bl0pbl33p@...il.com>,
        Linux API <linux-api@...r.kernel.org>
Subject: Re: pidfd design

On Mon, Mar 25, 2019 at 1:23 PM Daniel Colascione <dancol@...gle.com> wrote:
>
> On Mon, Mar 25, 2019 at 1:14 PM Jann Horn <jannh@...gle.com> wrote:
> >
> > On Mon, Mar 25, 2019 at 8:44 PM Andy Lutomirski <luto@...nel.org> wrote:

> > One ioctl on procfs roots to translate pidfds into that procfs,
> > subject to both the normal lookup permission checks and only working
> > if the pidfd has a translation into the procfs:
> >
> > int proc_root_fd = open("/proc", O_RDONLY);
> > int proc_dir_fd = ioctl(proc_root_fd, PROC_PIDFD_TO_PROCFSFD, pidfd);
> >
> > And one ioctl on procfs directories to translate from PGIDs and PIDs to pidfds:
> >
> > int proc_pgid_fd = open("/proc/self", O_RDONLY);
> > int self_pg_pidfd = ioctl(proc_pgid_fd, PROC_PROCFSFD_TO_PIDFD, 0);
> > int proc_pid_fd = open("/proc/thread-self", O_RDONLY);
> > int self_p_pidfd = ioctl(proc_pid_fd, PROC_PROCFSFD_TO_PIDFD, 0);
> >

This sounds okay to me.  Or we could make it so that a procfs
directory fd also works as a pidfd, but that seems more likely to be
problematic than just allowing two-way translation like this

> >
> > And then, as you proposed, the new sys_clone() can just return a
> > pidfd, and you can convert it into a procfs fd yourself if you want.
>
> I think that's the consensus we reached on the other thread. The
> O_DIRECTORY open on /proc/self/fd/mypidfd seems like it'd work well
> enough.

I must have missed this particular email.

IMO, if /proc/self/fd/mypidfd allows O_DIRECTORY open to work, then it
really ought to do function just like /proc/self/fd/mypidfd/. and
/proc/self/fd/mypidfd/status should work.  And these latter two
options seem nutty.

Also, this O_DIRECTORY thing is missing the entire point of the ioctl
interface -- it doesn't require procfs access.

--Andy