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

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Message-ID: <48B40D5F.3020705@linux.vnet.ibm.com>
Date:	Tue, 26 Aug 2008 16:04:15 +0200
From:	Pierre Morel <pmorel@...ux.vnet.ibm.com>
To:	Oleg Nesterov <oleg@...sign.ru>
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

Hello Oleg,

Oleg Nesterov wrote:
> On 08/25, Pierre Morel wrote:
>   
>> @@ -550,6 +550,23 @@ asmlinkage long sys_ptrace(long request,
>>  		goto out;
>>  	}
>>
>> +	if (request == PTRACE_SELF_ON) {
>> +		task_lock(current);
>> +		set_thread_flag(TIF_SYSCALL_TRACE);
>> +		current->ptrace |= PT_SELF;
>>     
>
> I didn't read the whole patch, but this sets PT_SELF without PT_PTRACED
> (and without ptrace_attach).
>   
Yes it is the way it is intended to work.
PT_SELF and other ptrace requests are not correlated,
I use the ptrace infrastructure to take advantage
of the existing system call interception framework.
> 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

The second solution seems easier, simpler and more
readable but extends the task struct.

What do you think is the best way to do it?

> Oleg.
>
>   
Thanks,

Pierre




-- 
=============
Pierre Morel
RTOS and Embedded Linux

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