linux-kernel - Re: [External] Re: [PATCH] mm/hugetlb: Fix a race between hugetlb sysctl handlers

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Message-ID: <CAMZfGtU9U5dv5oOCopnsFN7XErY52nA47b0jreUqZ2C6VBmC7w@mail.gmail.com>
Date:   Fri, 28 Aug 2020 10:33:40 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [External] Re: [PATCH] mm/hugetlb: Fix a race between hugetlb
 sysctl handlers

On Fri, Aug 28, 2020 at 5:51 AM Mike Kravetz <mike.kravetz@...cle.com> wrote:
>
> On 8/25/20 7:47 PM, Muchun Song wrote:
> >
> > CPU0:                                     CPU1:
> >                                           proc_sys_write
> > hugetlb_sysctl_handler                      proc_sys_call_handler
> > hugetlb_sysctl_handler_common                 hugetlb_sysctl_handler
> >   table->data = &tmp;                           hugetlb_sysctl_handler_common
> >                                                   table->data = &tmp;
> >     proc_doulongvec_minmax
> >       do_proc_doulongvec_minmax             sysctl_head_finish
> >         __do_proc_doulongvec_minmax
> >           i = table->data;
> >           *i = val;     // corrupt CPU1 stack
>
> Thanks Muchun!
> Can you please add this to the commit message.

OK, I will do that. Thanks.

>
> Also, when looking closer at the patch I do not think setting table->maxlen
> is necessary in these routines.  maxlen is set when the hugetlb ctl_table
> entries are defined and initialized.  This is not something you introduced.
> The unnecessary assignments are in the existing code.  However, there is no
> need to carry them forward.

Yeah, I agree with you. I will remove the unnecessary assignment of
table->maxlen.

>
> --
> Mike Kravetz



-- 
Yours,
Muchun