linux-kernel - Re: [PATCH] seccomp: fix the usage of get/put_seccomp_filter() in seccomp_get

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Message-ID: <20170922152229.GA19152@redhat.com>
Date:   Fri, 22 Sep 2017 17:22:29 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Chris Salls <chrissalls5@...il.com>,
        Andy Lutomirski <luto@...capital.net>,
        Will Drewry <wad@...omium.org>,
        "security@...nel.org" <security@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Tycho Andersen <tycho@...ker.com>
Subject: Re: [PATCH] seccomp: fix the usage of get/put_seccomp_filter() in
 seccomp_get_filter()

On 09/21, Kees Cook wrote:
>
> On Thu, Sep 21, 2017 at 3:57 AM, Oleg Nesterov <oleg@...hat.com> wrote:
> > On 09/20, Kees Cook wrote:
> >>
> >> Given how reference counting is done for filters, I'd be happier with
> >> leaving the get_seccomp_filter() as-is,
> >
> > No, please note that filter != tsk->seccomp.filter, get_seccomp_filter()
> > won't work.
>
> Ah yes, sorry, you're right.
>
> >> (i.e. don't open-code
> >> the refcount_inc()).
> >
> > agreed, probably another __get_seccomp_filter(filter) makes sense, especially
> > if we do other changes like get_nth().
> >
> > But imo not in this fix.
>
> Regardless, whatever lands will need backport adjustment for
> refcount_*/atomic_* in -stable.

yes, but this adjustment is trivial, and we will need it whatever we do
in this fix,

> Can you resend the two patches; I can send the backport to -stable manually...

Not sure I understand... Do you mean this fix + untested "introduce get_nth_filter()" ?

Can't we push this simple fix first? Then we can discuss the cleanups. Besides,
the 2nd patch connects to Tycho's "[PATCH] ptrace, seccomp: add support for
retrieving seccomp flags", otherwise it could be more simple.

Oleg.