netdev - Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE

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Date:	Mon, 27 Feb 2012 13:47:17 -0600
From:	Will Drewry <wad@...omium.org>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-doc@...r.kernel.org, kernel-hardening@...ts.openwall.com,
	netdev@...r.kernel.org, x86@...nel.org, arnd@...db.de,
	davem@...emloft.net, hpa@...or.com, mingo@...hat.com,
	peterz@...radead.org, rdunlap@...otime.net, mcgrathr@...omium.org,
	tglx@...utronix.de, luto@....edu, eparis@...hat.com,
	serge.hallyn@...onical.com, djm@...drot.org, scarybeasts@...il.com,
	indan@....nu, pmoore@...hat.com, akpm@...ux-foundation.org,
	corbet@....net, eric.dumazet@...il.com, markus@...omium.org,
	coreyb@...ux.vnet.ibm.com, keescook@...omium.org,
	Denys Vlasenko <dvlasenk@...hat.com>
Subject: Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support

On Mon, Feb 27, 2012 at 11:54 AM, Oleg Nesterov <oleg@...hat.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? I don't see
these in kernel-next yet and I can't tell if there is a public -mm
anywhere anymore.  I can use the patches from the mailing list with
Denys's changes if that'd be good enough.  His cleanup will make this
code even smaller!

>> --- 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.  (More follow-ups
to your reviews incoming too :).

Thanks!
will
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