linux-kernel - Re: [PATCH 4.9] mm: page_alloc: validate buddy page before using

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Date:   Fri, 17 Jun 2022 10:20:52 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Xianting Tian <xianting.tian@...ux.alibaba.com>
Cc:     akpm@...ux-foundation.org, ziy@...dia.com, stable@...r.kernel.org,
        guoren@...nel.org, huanyi.xj@...baba-inc.com, guohanjun@...wei.com,
        zjb194813@...baba-inc.com, tianhu.hh@...baba-inc.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4.9] mm: page_alloc: validate buddy page before using

On Fri, Jun 17, 2022 at 12:19:28AM +0800, Xianting Tian wrote:
> Commit 787af64d05cd ("mm: page_alloc: validate buddy before check its migratetype.")
> fixes a bug in 1dd214b8f21c and there is a similar bug in d9dddbf55667 that
> can be fixed in a similar way too.
> 
> In addition, for RISC-V arch the first 2MB RAM could be reserved for opensbi,
> so it would have pfn_base=512 and mem_map began with 512th PFN when
> CONFIG_FLATMEM=y.
> But __find_buddy_pfn algorithm thinks the start pfn 0, it could get 0 pfn or
> less than the pfn_base value. We need page_is_buddy() to verify the buddy to
> prevent accessing an invalid buddy.
> 
> Fixes: d9dddbf55667 ("mm/page_alloc: prevent merging between isolated and other pageblocks")
> Cc: stable@...r.kernel.org
> Reported-by: zjb194813@...baba-inc.com
> Reported-by: tianhu.hh@...baba-inc.com
> Signed-off-by: Xianting Tian <xianting.tian@...ux.alibaba.com>
> ---
>  mm/page_alloc.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index a6e682569e5b..1c423faa4b62 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -864,6 +864,9 @@ static inline void __free_one_page(struct page *page,
>  
>  			buddy_idx = __find_buddy_index(page_idx, order);
>  			buddy = page + (buddy_idx - page_idx);
> +
> +			if (!page_is_buddy(page, buddy, order))
> +				goto done_merging;
>  			buddy_mt = get_pageblock_migratetype(buddy);
>  
>  			if (migratetype != buddy_mt
> -- 
> 2.17.1
> 

What is the git commit id of this change in Linus's tree?

thanks,

greg k-h