linux-kernel - Re: Possible race in copy of fpu->state in copy

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Message-ID: <CAHz2CGXMaENy=CoO48ax6-UFiFdyfbRugBtBnwM9+7rFoaFykw@mail.gmail.com>
Date:	Wed, 13 Apr 2016 11:19:28 +0800
From:	Jianyu Zhan <nasa4836@...il.com>
To:	mingo@...hat.com, "H. Peter Anvin" <hpa@...or.com>,
	suresh.b.siddha@...el.com
Cc:	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Possible race in copy of fpu->state in copy_process against the
 exeve'ing parent?

On Wed, Apr 13, 2016 at 11:11 AM, Jianyu Zhan <nasa4836@...il.com> wrote:
>
> So  I suspect there is a possible race:
>
>
>    Parent:
>
>        sys_execve
>          do_execve
>            do_execve_common
>              search_binary_handler
>                 load_elf_binary
>                   start_thread
>                     start_thread_common
>                        free_thread_xstate(current)
>                          fpu_free
>                             fpu->state = NULL
>
>
>     Child:
>
>         sys_clone
>           do_fork
>              copy_process
>                 dup_task_struct
>                    prepare_to_copy
>                       unlazy_fpu
>                          __save_init_fpu
>                            fpu_save_init
>                              fpu_xsave(fpu)   <---- fpu->sate is NULL,
> so cause a
>                                                                 NULL
> dereference.
>

Hmm,  I am wrong, it is not Parent vs Child.

It is :   Parent  executes  sys_execuve,  and then right after that,
executes sys_clone.


 Regards,
 Jianyu Zhan