From: Aleksa Sarai <cyphar@cyphar.com>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Cc: Adrian Reber <areber@redhat.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Eric Biederman <ebiederm@xmission.com>,
Pavel Emelyanov <ovzxemul@gmail.com>,
Oleg Nesterov <oleg@redhat.com>,
Dmitry Safonov <0x7f454c46@gmail.com>,
Andrei Vagin <avagin@gmail.com>,
lkml <linux-kernel@vger.kernel.org>,
Mike Rapoport <rppt@linux.ibm.com>,
Radostin Stoyanov <rstoyanov1@gmail.com>,
Arnd Bergmann <arnd@arndb.de>,
Cyrill Gorcunov <gorcunov@openvz.org>,
Thomas Gleixner <tglx@linutronix.de>,
Linux API <linux-api@vger.kernel.org>
Subject: Re: clone3: allow creation of time namespace with offset
Date: Wed, 18 Mar 2020 01:23:50 +1100 [thread overview]
Message-ID: <20200317142350.ssraami3a4vnk5po@yavin> (raw)
In-Reply-To: <CAKgNAkh7=2Noyn0o3880xbbi4w5oiwqs9ibTYLtheqzxne3mbQ@mail.gmail.com>
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On 2020-03-17, Michael Kerrisk (man-pages) <mtk.manpages@gmail.com> wrote:
> [CC += linux-api; please CC on future versions]
>
> On Tue, 17 Mar 2020 at 09:32, Adrian Reber <areber@redhat.com> wrote:
> > Requiring nanoseconds as well as seconds for two clocks during clone3()
> > means that it would require 4 additional members to 'struct clone_args':
> >
> > __aligned_u64 tls;
> > __aligned_u64 set_tid;
> > __aligned_u64 set_tid_size;
> > + __aligned_u64 boottime_offset_seconds;
> > + __aligned_u64 boottime_offset_nanoseconds;
> > + __aligned_u64 monotonic_offset_seconds;
> > + __aligned_u64 monotonic_offset_nanoseconds;
> > };
> >
> > To avoid four additional members to 'struct clone_args' this patchset
> > uses another approach:
> >
> > __aligned_u64 tls;
> > __aligned_u64 set_tid;
> > __aligned_u64 set_tid_size;
> > + __aligned_u64 timens_offset;
> > + __aligned_u64 timens_offset_size;
> > };
> >
> > timens_offset is a pointer to an array just as previously done with
> > set_tid and timens_offset_size is the size of the array.
> >
> > The timens_offset array is expected to contain a struct like this:
> >
> > struct set_timens_offset {
> > int clockid;
> > struct timespec val;
> > };
> >
> > This way it is possible to pass the information of multiple clocks with
> > seconds and nanonseconds to clone3().
> >
> > To me this seems the better approach, but I am not totally convinced
> > that it is the right thing. If there are other ideas how to pass two
> > clock offsets with seconds and nanonseconds to clone3() I would be happy
> > to hear other ideas.
While I agree this does make the API cleaner, I am a little worried that
it risks killing some of the ideas we discussed for seccomp deep
inspection. In particular, having a pointer to variable-sized data
inside the struct means that now the cBPF program can't just be given a
copy of the struct data from userspace to check.
I'm sure it's a solveable problem (and it was one we were bound to run
into at some point), it'll just mean we'll need a more complicated way
of filtering such syscalls.
--
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>
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next prev parent reply other threads:[~2020-03-19 8:11 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200317083043.226593-1-areber@redhat.com>
2020-03-17 9:40 ` clone3: allow creation of time namespace with offset Michael Kerrisk (man-pages)
2020-03-17 14:23 ` Aleksa Sarai [this message]
2020-03-17 16:09 ` Christian Brauner
[not found] ` <CAK8P3a2-qQhpRdF0+iVrpp=vEvgwtndQL89CUm_QzoW2QYX1Jw@mail.gmail.com>
2020-03-19 8:11 ` Adrian Reber
2020-03-19 8:16 ` Arnd Bergmann
2020-03-19 10:29 ` Christian Brauner
2020-03-20 18:33 ` Andrei Vagin
2020-03-24 16:09 ` Christian Brauner
2020-03-24 16:25 ` Adrian Reber
2020-03-24 17:56 ` Christian Brauner
2020-03-25 7:58 ` Adrian Reber
2020-03-25 11:26 ` Christian Brauner
2020-04-01 11:40 ` Michael Kerrisk (man-pages)
2020-04-01 11:46 ` Christian Brauner
2020-04-01 12:15 ` Michael Kerrisk (man-pages)
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