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

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Date:   Mon, 24 Aug 2020 13:59:24 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Muchun Song <songmuchun@...edance.com>
Cc:     mike.kravetz@...cle.com, npiggin@...e.de, agl@...ibm.com,
        ak@...ux.intel.com, nacc@...ibm.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: Fix a race between hugetlb sysctl handlers

On Sat, 22 Aug 2020 17:53:28 +0800 Muchun Song <songmuchun@...edance.com> wrote:

> There is a race between the assignment of `table->data` and write value
> to the pointer of `table->data` in the __do_proc_doulongvec_minmax().

Where does __do_proc_doulongvec_minmax() write to table->data?

I think you're saying that there is a race between the assignment of
ctl_table->table in hugetlb_sysctl_handler_common() and the assignment
of the same ctl_table->table in hugetlb_overcommit_handler()?

Or not, maybe I'm being thick.  Can you please describe the race more
carefully and completely?

> Fix this by duplicating the `table`, and only update the duplicate of
> it. And introduce a helper of proc_hugetlb_doulongvec_minmax() to
> simplify the code.
>