linux-kernel - Re: [PATCH] syscalls: Document OCI seccomp filter interactions & workaround

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:   Tue, 24 Nov 2020 19:02:53 +0100
From:   Florian Weimer <fweimer@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Kees Cook <keescook@...omium.org>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>, Mark Wielaard <mark@...mp.org>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Linux API <linux-api@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        kernel list <linux-kernel@...r.kernel.org>,
        dev@...ncontainers.org, Jonathan Corbet <corbet@....net>,
        "Carlos O'Donell" <carlos@...hat.com>
Subject: Re: [PATCH] syscalls: Document OCI seccomp filter interactions &
 workaround

* Jann Horn:

> +seccomp maintainers/reviewers
> [thread context is at
> https://lore.kernel.org/linux-api/87lfer2c0b.fsf@oldenburg2.str.redhat.com/
> ]
>
> On Tue, Nov 24, 2020 at 5:49 PM Christoph Hellwig <hch@...radead.org> wrote:
>> On Tue, Nov 24, 2020 at 03:08:05PM +0100, Mark Wielaard wrote:
>> > For valgrind the issue is statx which we try to use before falling back
>> > to stat64, fstatat or stat (depending on architecture, not all define
>> > all of these). The problem with these fallbacks is that under some
>> > containers (libseccomp versions) they might return EPERM instead of
>> > ENOSYS. This causes really obscure errors that are really hard to
>> > diagnose.
>>
>> So find a way to detect these completely broken container run times
>> and refuse to run under them at all.  After all they've decided to
>> deliberately break the syscall ABI.  (and yes, we gave the the rope
>> to do that with seccomp :().
>
> FWIW, if the consensus is that seccomp filters that return -EPERM by
> default are categorically wrong, I think it should be fairly easy to
> add a check to the seccomp core that detects whether the installed
> filter returns EPERM for some fixed unused syscall number and, if so,
> prints a warning to dmesg or something along those lines...

But that's playing Core Wars, right?  Someone will write a seccomp
filter trying to game that kernel check.  I don't really think it solves
anything until there is consensus what a system call filter should do
with system calls not on the permitted list.

Thanks,
Florian
-- 
Red Hat GmbH, https://de.redhat.com/ , Registered seat: Grasbrunn,
Commercial register: Amtsgericht Muenchen, HRB 153243,
Managing Directors: Charles Cachera, Brian Klemm, Laurie Krebs, Michael O'Neill