From: Matthew Wilcox <willy@infradead.org>
To: zhenwei pi <pizhenwei@bytedance.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
akpm@linux-foundation.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm: fix kernel NULL pointer dereference in page_vma_mapped_walk
Date: Thu, 7 Apr 2022 15:17:27 +0100 [thread overview]
Message-ID: <Yk7yd5ho2a7jWNfS@casper.infradead.org> (raw)
In-Reply-To: <Yk7tIi4UKjiqQyoF@casper.infradead.org>
On Thu, Apr 07, 2022 at 02:54:42PM +0100, Matthew Wilcox wrote:
> On Thu, Apr 07, 2022 at 02:40:08PM +0800, zhenwei pi wrote:
> > size_to_hstate(4K) returns NULL pointer, this leads kernel BUG in
> > function page_vma_mapped_walk.
>
> Yes, I think this is the right fix. It's not immediately obvious from
> the bug and the patch, but what's going on is:
>
> page_mapped_in_vma() sets nr_pages to 1. This is correct because we
> usually only want to know about the precise page, and not about the
> folio containing it. But hugetlbfs is special (... in so many ways ...)
> and actually wants to work on the entire folio. We could set nr_pages
> specially for hugetlb pages, but it's better to ignore it in
> page_vma_mapped_walk() for the hugetlb case.
>
> I'll fix up the changelog and add it to my pile of fixes that I'm
> sending tomorrow.
> https://git.infradead.org/users/willy/pagecache.git/shortlog/refs/heads/for-next
I looked over the patch in context, and realised we now don't need to
call size_to_hstate since we're getting the hstate from the VMA.
https://git.infradead.org/users/willy/pagecache.git/commitdiff/98ea02597b9967c0817d29fee2f96d21b9e59ca5
next prev parent reply other threads:[~2022-04-07 14:17 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-07 6:40 [PATCH] mm: fix kernel NULL pointer dereference in page_vma_mapped_walk zhenwei pi
2022-04-07 9:31 ` Muchun Song
2022-04-07 13:54 ` Matthew Wilcox
2022-04-07 14:17 ` Matthew Wilcox [this message]
2022-04-08 1:17 ` zhenwei pi
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