linux-kernel - Re: [RFC] [Patch 1/1] [Self Ptrace] System call notification with self

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Message-ID: <20080826162750.GA406@tv-sign.ru>
Date:	Tue, 26 Aug 2008 20:27:50 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Roland McGrath <roland@...hat.com>,
	Heiko Carstens <heicars2@...ux.vnet.ibm.com>,
	sameske@...ux.vnet.ibm.com,
	Martin Schwidefsky <schwidefsky@...ibm.com>
Subject: Re: [RFC] [Patch 1/1] [Self Ptrace] System call notification with self_ptrace

On 08/26, Pierre Morel wrote:
>
> Oleg Nesterov wrote:
> >We have some "->ptrace != 0" checks which can misunderstand this. Just
> >for example, suppose that the task does sys_ptrace(PTRACE_SELF_ON) and
> >then its parent dies. I guess in that case forget_original_parent()
> >will hit BUG_ON(p->ptrace), no?
> >
> >
> Yes you are right, I will take care of those cases.
> I have the choice between:
>
> - tracking all references to the ptrace flags and add a test for PT_SELF
> or a mask.
>
> - add a dedicated task_struct entry to hold the PT_SELF flag

Well, given that PT_SELF is exotic, neither choice looks very good, imho.
But I am not expert and maintainer is cc'ed ;)

I don't understand why this patch changes the x86's sys_sigaction().
On s390 the patch changes handle_signal(), this is not clear to me too.
do_syscall_trace() filters out __NR_ptrace, this afaics means that the
handler for SIGSYS can happily call sys_ptrace(PTRACE_SELF_OFF) and
clear PT_SELF/TIF_SYSCALL_TRACE.

I must admit, personally I don't think the whole idea is good...
And what if the user of PT_SELF is ptraced? The usage of TIF_SYSCALL_TRACE
doesn't look "safe" in that case.

Isn't it possible to implement this behaviour in the user space? If the
task needs the PT_SELF behaviour, it can fork another process which will
do PTRACE_ATTACH and then send the notifications to the task. We can use
signals or something else.

Oleg.

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