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From: Andy Lutomirski <luto@kernel.org>
To: Christian Brauner <christian@brauner.io>
Cc: ksummit <ksummit-discuss@lists.linuxfoundation.org>
Subject: Re: [Ksummit-discuss] [TECH TOPIC] seccomp
Date: Fri, 19 Jul 2019 05:32:59 -0700
Message-ID: <CALCETrVpbSDraiwJRmOj28wepTjEPiSDQz=DUuSig_P1rSGZ6Q@mail.gmail.com> (raw)
In-Reply-To: <20190719093538.dhyopljyr5ns33qx@brauner.io>

On Fri, Jul 19, 2019 at 2:35 AM Christian Brauner <christian@brauner.io> wrote:
>
> In light of all this, I would argue that we should seriously look into
> extending seccomp to allow filtering on pointer arguments.

I won't be at LPC this year, but I was thinking about this anyway.  I
have the following suggestion that might be a bit unorthodox: have
syscalls opt into this filtering.  Specifically, a syscall that
supports pointer filtering would be refactored the way a bunch of our
syscalls are already refactored.  The baseline situation is:

SYSCALL_DEFINE1(syscallname, struct foo __user *, buf) { ... }

Instead, we would do:

SYSCALL_FILTERABLE(syscallname, struct foo __user *, buf)
{
  int ret;
  struct foo kbuf;
  ret = copy_from_user(&kbuf, buf, sizeof(buf));
  if (ret)
    return ret;

  ret = seccomp_deep_filter(syscallname, 0, &kbuf);
  if (ret)
    return ret;

  return do_syscallname(&kbuf);
}

In principle, if we know we're doing a FILTERABLE syscall, we could
skip the initial seccomp invocation and just defer it until
seccomp_deep_filter(), although this might interact badly with any
SECCOMP_RET_PTRACE handles that change nr.

To make this robust, it might help a lot if the generation of these
stubs was mostly automated.

  reply index

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-19  9:35 Christian Brauner
2019-07-19 12:32 ` Andy Lutomirski [this message]
2019-07-20  3:18   ` Kees Cook
2019-08-14 17:54     ` Andy Lutomirski
2019-08-15 17:48       ` Kees Cook
2019-08-15 18:26         ` Andy Lutomirski
2019-08-15 18:31           ` Christian Brauner
2019-08-15 19:21             ` Andy Lutomirski
2019-07-20  7:23 ` James Morris
2019-07-20  7:41   ` Christian Brauner
2019-07-25 14:18     ` Serge E. Hallyn

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