linux-kernel - Re: [PATCH] mm, vmstat: Fix NULL pointer dereference during pagetypeinfo print

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Date:   Fri, 19 May 2017 16:48:56 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Firo Yang <firogm@...il.com>
Cc:     akpm@...ux-foundation.org, vbabka@...e.cz,
        mgorman@...hsingularity.net, hannes@...xchg.org,
        bigeasy@...utronix.de, iamjoonsoo.kim@....com, rientjes@...gle.com,
        hughd@...gle.com, cl@...ux.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm, vmstat: Fix NULL pointer dereference during
 pagetypeinfo print

On Fri 19-05-17 22:39:36, Firo Yang wrote:
> During showing the pagetypeinfo, we forgot to save the found page
> and dereference a invalid page address from the stack.
> 
> To fix it, save and reference the page address returned by
> pfn_to_online_page().

Thanks for taking catching that and your fix. I have already posted a fix
http://lkml.kernel.org/r/20170519072225.GA13041@dhcp22.suse.cz earlier
today. Sorry about troubles

> Signed-off-by: Firo Yang <firogm@...il.com>
> ---
>  mm/vmstat.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index c432e58..6dae6b2 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1223,7 +1223,8 @@ static void pagetypeinfo_showblockcount_print(struct seq_file *m,
>  	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
>  		struct page *page;
>  
> -		if (!pfn_to_online_page(pfn))
> +		page = pfn_to_online_page(pfn);
> +		if (!page)
>  			continue;
>  
>  		/* Watch for unexpected holes punched in the memmap */
> -- 
> 2.9.4
> 

-- 
Michal Hocko
SUSE Labs