From: Oleg Nesterov <oleg@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Alexei Starovoitov <ast@plumgrid.com>,
Andrew Morton <akpm@linux-foundation.org>,
Daniel Borkmann <dborkman@redhat.com>,
Will Drewry <wad@chromium.org>, Julien Tinnes <jln@chromium.org>,
David Drysdale <drysdale@google.com>,
Linux API <linux-api@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
linux-mips@linux-mips.org,
linux-arch <linux-arch@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v9 09/11] seccomp: introduce writer locking
Date: Thu, 10 Jul 2014 17:24:18 +0200 [thread overview]
Message-ID: <20140710152418.GB20861@redhat.com> (raw)
In-Reply-To: <CAGXu5jL6q1d16uA1Yu+QO4eV7zWwcWEWgkZrwmsfymbMvEr6+Q@mail.gmail.com>
On 07/10, Kees Cook wrote:
>
> On Wed, Jul 9, 2014 at 11:55 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > On 07/09, Oleg Nesterov wrote:
> >>
> >> On 06/27, Kees Cook wrote:
> >> >
> >> > static u32 seccomp_run_filters(int syscall)
> >> > {
> >> > - struct seccomp_filter *f;
> >> > + struct seccomp_filter *f = ACCESS_ONCE(current->seccomp.filter);
> >>
> >> I am not sure...
> >>
> >> This is fine if this ->filter is the 1st (and only) one, in this case
> >> we can rely on rmb() in the caller.
> >>
> >> But the new filter can be installed at any moment. Say, right after that
> >> rmb() although this doesn't matter. Either we need smp_read_barrier_depends()
> >> after that, or smp_load_acquire() like the previous version did?
> >
> > Wait... and it seems that seccomp_sync_threads() needs smp_store_release()
> > when it sets thread->filter = current->filter by the same reason?
> >
> > OTOH. smp_store_release() in seccomp_attach_filter() can die, "current"
> > doesn't need a barrier to serialize with itself.
>
> I have lost track of what you're suggesting to change. :)
Perhaps I am just trying to confuse you and myself ;)
But,
> Since rmb() happens before run_filters, isn't the ACCESS_ONCE
> sufficient?
Yes. But see above. ACCESS_ONCE is sufficient if we read the first filter
installed by another thread, in this case rmb() pairs with mb_before_atomic()
before set_bit(TIF_SECCOMP).
IOW, if this threads sees TIF_SECCOMP, it should also see all modifications
which were done before set_bit, including the data in ->filter points to.
> We only care that TIF_SECCOMP, mode, and some filter is
> valid. In a tsync thread race, it's okay to use not use the deepest
> filter node in the list,
Yes, it is fine if we miss yet another filter which was just installed by
another thread.
But, unless I missed something, the problem is that we can get this new
filter.
Just to simplify. Suppose TIF_SECCOMP was set a long ago. This thread
has a single filter F1 and it enters seccomp_run_filters().
Right before it does ACCESS_ONCE() to read the pointer, another thread
does seccomp_sync_threads() and sets .filter = F2.
If ACCESS_ONCE() returns F1 - everything is fine. But it can see the new
pointer F2, and in this case we need a barrier to ensure that, say,
LOAD(F2->prog) will see all the preceding changes in this memory.
Oleg.
next prev parent reply other threads:[~2014-07-10 15:24 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-27 23:22 [PATCH v9 0/11] seccomp: add thread sync ability Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 01/11] seccomp: create internal mode-setting function Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 02/11] seccomp: extract check/assign mode helpers Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 03/11] seccomp: split mode setting routines Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 04/11] seccomp: add "seccomp" syscall Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 05/11] ARM: add seccomp syscall Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 06/11] MIPS: " Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 07/11] sched: move no_new_privs into new atomic flags Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 08/11] seccomp: split filter prep from check and apply Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:22 ` [PATCH v9 09/11] seccomp: introduce writer locking Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-07-09 18:42 ` Oleg Nesterov
2014-07-09 18:42 ` Oleg Nesterov
2014-07-09 18:55 ` Oleg Nesterov
2014-07-09 18:55 ` Oleg Nesterov
2014-07-10 9:25 ` Kees Cook
2014-07-10 15:24 ` Oleg Nesterov [this message]
2014-07-10 15:24 ` Oleg Nesterov
2014-07-10 16:54 ` Kees Cook
2014-07-10 16:54 ` Kees Cook
2014-07-10 17:35 ` Oleg Nesterov
2014-07-10 17:35 ` Oleg Nesterov
2014-07-09 18:59 ` Oleg Nesterov
2014-07-09 18:59 ` Oleg Nesterov
2014-06-27 23:22 ` [PATCH v9 10/11] seccomp: allow mode setting across threads Kees Cook
2014-06-27 23:22 ` Kees Cook
2014-06-27 23:23 ` [PATCH v9 11/11] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC Kees Cook
2014-06-27 23:23 ` Kees Cook
2014-07-09 18:05 ` Oleg Nesterov
2014-07-09 18:05 ` Oleg Nesterov
2014-07-10 9:17 ` Kees Cook
2014-07-10 9:17 ` Kees Cook
2014-07-10 15:08 ` Oleg Nesterov
2014-07-10 15:08 ` Oleg Nesterov
[not found] ` <20140710150832.GA20861-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2014-07-10 16:03 ` Kees Cook
2014-07-10 16:03 ` Kees Cook
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