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From: "Dmitry V. Levin" <ldv-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>
To: Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Eugene Syromyatnikov
	<esyr-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Steven Rostedt <rostedt-nx8X9YLhiw1AfugRpC6u6w@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Ingo Molnar <mingo-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	strace-devel-3+4lAyCyj6AWlMsSdNXQLw@public.gmane.org
Subject: Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL_INFO
Date: Wed, 28 Nov 2018 02:27:53 +0300	[thread overview]
Message-ID: <20181127232753.GA18755@altlinux.org> (raw)
In-Reply-To: <20181127123116.GA13284-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>


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On Tue, Nov 27, 2018 at 01:31:17PM +0100, Oleg Nesterov wrote:
> On 11/27, Elvira Khabirova wrote:
> > On Mon, 26 Nov 2018 15:35:24 +0100, Oleg Nesterov wrote:
> > > On 11/25, Elvira Khabirova wrote:
> > > >
> > > > Extend PTRACE_GET_SYSCALL_INFO to support PTRACE_EVENT_SECCOMP stops.
> > > > The information returned is the same as for syscall-enter-stops.
> > >
> > > Oh, this is not nice ;) there must be a better option, I hope... Plus
> > >
> > >
> > > Can't ptrace_get_syscall() check
> > >
> > > 	child->exit_code == (PTRACE_EVENT_SECCOMP << 8) | SIGTRAP;
> > >
> > > to detect the PTRACE_EVENT_SECCOMP case?
> >
> > Nope; looks like exit_code is zeroed after wait().
> 
> Yes, thanks for correcting me,
> 
> but we can use child->last_siginfo->si_code.

Yes, this approach works, thanks!

> Just like ptrace_request(PTRACE_LISTEN)
> does but you can do this lockless (no need to lock_task_sighand()).

Why this can be done lockless?  All other places in that file do
the locking, so I'd rather add a comment in the new code.

> And if we require that the user of ptrace_get_syscall() should also use TRACESYSGOOD
> then ptrace_get_syscall() can probably do something like
> 
> 	int entry;
> 
> 	if (!child->last_siginfo)
> 		return -EINVAL;
> 	else if (child->last_siginfo->si_code == (PTRACE_EVENT_SECCOMP << 8) | SIGTRAP)
> 		entry = 1;
> 	else if (child->last_siginfo->si_code == SIGTRAP | 0x80)
> 		entry = child->ptrace_message == PTRACE_EVENTMSG_SYSCALL_ENTRY;
> 	else
> 		return -EINVAL;
> 
> and this way PTRACE_EVENTMSG_SYSCALL_ENTRY/EXIT can't confict with seccomp or
> anything else.
> 
> No?
> 
> Of course, debugger can do PTRACE_SETSIGINFO and confuse itself but probably we
> do not care?

The only potential issue I could think of is whether PTRACE_SETSIGINFO
could be used this way to cause an information leak by making
PTRACE_GET_SYSCALL_INFO access some unrelated data.


-- 
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WARNING: multiple messages have this Message-ID (diff)
From: "Dmitry V. Levin" <ldv@altlinux.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Elvira Khabirova <lineprinter@altlinux.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Ingo Molnar <mingo@redhat.com>,
	Eugene Syromyatnikov <esyr@redhat.com>,
	Andy Lutomirski <luto@kernel.org>,
	strace-devel@lists.strace.io, linux-api@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL_INFO
Date: Wed, 28 Nov 2018 02:27:53 +0300	[thread overview]
Message-ID: <20181127232753.GA18755@altlinux.org> (raw)
In-Reply-To: <20181127123116.GA13284@redhat.com>

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On Tue, Nov 27, 2018 at 01:31:17PM +0100, Oleg Nesterov wrote:
> On 11/27, Elvira Khabirova wrote:
> > On Mon, 26 Nov 2018 15:35:24 +0100, Oleg Nesterov wrote:
> > > On 11/25, Elvira Khabirova wrote:
> > > >
> > > > Extend PTRACE_GET_SYSCALL_INFO to support PTRACE_EVENT_SECCOMP stops.
> > > > The information returned is the same as for syscall-enter-stops.
> > >
> > > Oh, this is not nice ;) there must be a better option, I hope... Plus
> > >
> > >
> > > Can't ptrace_get_syscall() check
> > >
> > > 	child->exit_code == (PTRACE_EVENT_SECCOMP << 8) | SIGTRAP;
> > >
> > > to detect the PTRACE_EVENT_SECCOMP case?
> >
> > Nope; looks like exit_code is zeroed after wait().
> 
> Yes, thanks for correcting me,
> 
> but we can use child->last_siginfo->si_code.

Yes, this approach works, thanks!

> Just like ptrace_request(PTRACE_LISTEN)
> does but you can do this lockless (no need to lock_task_sighand()).

Why this can be done lockless?  All other places in that file do
the locking, so I'd rather add a comment in the new code.

> And if we require that the user of ptrace_get_syscall() should also use TRACESYSGOOD
> then ptrace_get_syscall() can probably do something like
> 
> 	int entry;
> 
> 	if (!child->last_siginfo)
> 		return -EINVAL;
> 	else if (child->last_siginfo->si_code == (PTRACE_EVENT_SECCOMP << 8) | SIGTRAP)
> 		entry = 1;
> 	else if (child->last_siginfo->si_code == SIGTRAP | 0x80)
> 		entry = child->ptrace_message == PTRACE_EVENTMSG_SYSCALL_ENTRY;
> 	else
> 		return -EINVAL;
> 
> and this way PTRACE_EVENTMSG_SYSCALL_ENTRY/EXIT can't confict with seccomp or
> anything else.
> 
> No?
> 
> Of course, debugger can do PTRACE_SETSIGINFO and confuse itself but probably we
> do not care?

The only potential issue I could think of is whether PTRACE_SETSIGINFO
could be used this way to cause an information leak by making
PTRACE_GET_SYSCALL_INFO access some unrelated data.


-- 
ldv

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  parent reply	other threads:[~2018-11-27 23:27 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-25  1:21 [PATCH RESEND v3 0/3] ptrace: add PTRACE_GET_SYSCALL_INFO request Elvira Khabirova
2018-11-25  1:21 ` Elvira Khabirova
2018-11-25  1:22 ` [PATCH RESEND v3 1/3] ptrace: pass type of a syscall-stop in ptrace_message Elvira Khabirova
2018-11-25  1:22   ` Elvira Khabirova
2018-11-25  1:54   ` Joey Pabalinas
     [not found]     ` <20181125015402.glcaw3kghcu4pr22-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2018-11-25  2:10       ` Dmitry V. Levin
2018-11-25  2:10         ` Dmitry V. Levin
     [not found]         ` <20181125021059.GA1190-u2l5PoMzF/Vg9hUCZPvPmw@public.gmane.org>
2018-11-25  6:17           ` Joey Pabalinas
2018-11-25  6:17             ` Joey Pabalinas
2018-11-26 14:56   ` Oleg Nesterov
     [not found]     ` <20181126145643.GD1660-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-27  2:53       ` Elvira Khabirova
2018-11-27  2:53         ` Elvira Khabirova
2018-11-27  3:48         ` Dmitry V. Levin
2018-11-25  1:23 ` [PATCH RESEND v3 2/3] ptrace: add PTRACE_GET_SYSCALL_INFO request Elvira Khabirova
2018-11-25  1:23   ` Elvira Khabirova
2018-11-25  1:23 ` [RFC PATCH RESEND v3 3/3] ptrace: add PTRACE_EVENT_SECCOMP support to PTRACE_GET_SYSCALL_INFO Elvira Khabirova
2018-11-25  1:23   ` Elvira Khabirova
2018-11-26 14:35   ` Oleg Nesterov
2018-11-26 14:35     ` Oleg Nesterov
     [not found]     ` <20181126143524.GB1660-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-27  3:07       ` Elvira Khabirova
2018-11-27  3:07         ` Elvira Khabirova
2018-11-27  3:21         ` Dmitry V. Levin
2018-11-27  3:21           ` Dmitry V. Levin
2018-11-27 12:31         ` Oleg Nesterov
     [not found]           ` <20181127123116.GA13284-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-27 23:27             ` Dmitry V. Levin [this message]
2018-11-27 23:27               ` Dmitry V. Levin
2018-11-28 12:35               ` Oleg Nesterov
     [not found]                 ` <20181128123545.GA30395-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2018-11-28 12:44                   ` Dmitry V. Levin
2018-11-28 12:44                     ` Dmitry V. Levin
2018-11-28 13:13                     ` Oleg Nesterov

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