Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support

From: Will Drewry <wad@chromium.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
	linux-doc@vger.kernel.org, kernel-hardening@lists.openwall.com,
	netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
	davem@davemloft.net, hpa@zytor.com, mingo@redhat.com,
	peterz@infradead.org, rdunlap@xenotime.net,
	mcgrathr@chromium.org, tglx@linutronix.de, luto@mit.edu,
	eparis@redhat.com, serge.hallyn@canonical.com, djm@mindrot.org,
	scarybeasts@gmail.com, indan@nul.nu, pmoore@redhat.com,
	akpm@linux-foundation.org, corbet@lwn.net,
	eric.dumazet@gmail.com, markus@chromium.org,
	coreyb@linux.vnet.ibm.com, keescook@chromium.org,
	Denys Vlasenko <dvlasenk@redhat.com>
Subject: Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support
Date: Tue, 28 Feb 2012 11:04:01 -0600	[thread overview]
Message-ID: <CABqD9hY7=DpxWzf3+WNsK=LuLrabf=oHxyy+CQgu0JLxZ80zPQ@mail.gmail.com> (raw)
In-Reply-To: <20120228164335.GC3664@redhat.com>

On Tue, Feb 28, 2012 at 10:43 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> On 02/27, Will Drewry wrote:
>> On Mon, Feb 27, 2012 at 11:54 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> > On 02/24, Will Drewry wrote:
>> >>
>> >>  arch/Kconfig              |    1 +
>> >>  include/linux/ptrace.h    |    7 +++++--
>> >>  include/linux/seccomp.h   |    4 +++-
>> >>  include/linux/tracehook.h |    6 ++++++
>> >>  kernel/ptrace.c           |    4 ++++
>> >>  kernel/seccomp.c          |   18 ++++++++++++++++++
>> >
>> > FYI, this conflicts with the changes -mm tree.
>> >
>> > The changes in ptrace.* confict with Denys's
>> > "ptrace: simplify PTRACE_foo constants and PTRACE_SETOPTIONS code"
>> >
>> > The change in tracehook.h conflicts with
>> > "ptrace: the killed tracee should not enter the syscall"
>>
>> What's the best way to reconcile this in this day and age?
>
> Of course I'd prefer if you make this change on top of Denys's patch ;)
>
> Besides, if you agree with PTRACE_EVENT_SECCOMP/PTRACE_O_SECCOMP you
> need only one trivial change in ptrace.h.

I think that works quite well :)

>> I don't see
>> these in kernel-next yet and I can't tell if there is a public -mm
>> anywhere anymore.
>
> Strange... I didn't check, but every patch in
> http://marc.info/?l=linux-mm-commits has this note:
>
>        The -mm tree is included into linux-next and is updated
>        there every 3-4 working days

It appears to have been pulled in ~8 hours ago.  I'm rebasing to next now.

>> >> --- a/kernel/seccomp.c
>> >> +++ b/kernel/seccomp.c
>> >> @@ -354,6 +354,24 @@ int __secure_computing_int(int this_syscall)
>> >>                       seccomp_send_sigsys(this_syscall, reason_code);
>> >>                       return -1;
>> >>               }
>> >> +             case SECCOMP_RET_TRACE: {
>> >> +                     int ret;
>> >> +                     struct pt_regs *regs = task_pt_regs(current);
>> >> +                     if (!(test_tsk_thread_flag(current, TIF_SYSCALL_TRACE)) ||
>> >> +                         !(current->ptrace & PT_TRACE_SECCOMP))
>> >> +                             return -1;
>> >> +                     /*
>> >> +                      * PT_TRACE_SECCOMP and seccomp.trace indicate whether
>> >> +                      * tracehook_report_syscall_entry needs to signal the
>> >> +                      * tracer.  This avoids race conditions in hand off and
>> >> +                      * the requirement for TIF_SYSCALL_TRACE ensures that
>> >> +                      * we are in the syscall slow path.
>> >> +                      */
>> >> +                     current->seccomp.trace = 1;
>> >> +                     ret = tracehook_report_syscall_entry(regs);
>> >> +                     current->seccomp.trace = 0;
>> >> +                     return ret;
>> >
>> > To be honest, this interface looks a bit strange to me...
>> >
>> > Once again, sorry if this was already discussed. But perhaps it would
>> > be better to introduce PTRACE_EVENT_SECCOMP/PTRACE_O_SECCOMP instead?
>> >
>> > SECCOMP_RET_TRACE: could simply do ptrace_event(PTRACE_EVENT_SECCOMP)
>> > unconditionaly. The tracer can set the option and do PTRACE_CONT if it
>> > doesn't want the system call notifications.
>>
>> Works for me - this also gets rid of the extra int for brief state
>> tracking. I'll switch over to that in the next rev.
>
> Great. In this case this patch becomes really trivial. Just 2 defines
> in ptrace.h and the unconditional ptrace_event() under SECCOMP_RET_TRACE.
>
> But probably you should check fatal_signal_pending(current) after
> ptrace_event() returns, ptrace_event() returns void.

Ah yeah - I don't want to reintroduce that issue :)

Thanks!