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Date: Tue, 28 Feb 2012 17:43:35 +0100
From: Oleg Nesterov <oleg@...hat.com>
To: Will Drewry <wad@...omium.org>
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,
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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 02/27, Will Drewry wrote:
> 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?
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 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
> >> --- 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.
Oleg.
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