linux-kernel - Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in hugetlb_mcopy_atomic

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Date:   Wed, 13 Jul 2022 10:23:57 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     <mike.kravetz@...cle.com>, <songmuchun@...edance.com>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm/hugetlb: avoid corrupting page->mapping in
 hugetlb_mcopy_atomic_pte

On Tue, 12 Jul 2022 21:05:42 +0800 Miaohe Lin <linmiaohe@...wei.com> wrote:

> In MCOPY_ATOMIC_CONTINUE case with a non-shared VMA, pages in the page
> cache are installed in the ptes. But hugepage_add_new_anon_rmap is called
> for them mistakenly because they're not vm_shared. This will corrupt the
> page->mapping used by page cache code.

Well that sounds bad.  And theories on why this has gone unnoticed for
over a year?  I assume this doesn't have coverage in our selftests?

> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -6038,7 +6038,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
>  	if (!huge_pte_none_mostly(huge_ptep_get(dst_pte)))
>  		goto out_release_unlock;
>  
> -	if (vm_shared) {
> +	if (page_in_pagecache) {
>  		page_dup_file_rmap(page, true);
>  	} else {
>  		ClearHPageRestoreReserve(page);
> -- 
> 2.23.0