linux-kernel - Re: [PATCH] mm/compaction: fix UBSAN shift-out-of-bounds warning

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Message-ID: <71a9cabf-974e-08bf-45b6-e760425ec6cc@huaweicloud.com>
Date: Thu, 23 Jan 2025 14:19:56 +0800
From: Kemeng Shi <shikemeng@...weicloud.com>
To: Liu Shixin <liushixin2@...wei.com>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Kefeng Wang <wangkefeng.wang@...wei.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Mel Gorman <mgorman@...hsingularity.net>,
 David Hildenbrand <david@...hat.com>, Matthew Wilcox <willy@...radead.org>,
 Nanyong Sun <sunnanyong@...wei.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/compaction: fix UBSAN shift-out-of-bounds warning



on 1/23/2025 10:10 AM, Liu Shixin wrote:
> syzkaller reported a UBSAN shift-out-of-bounds warning of (1UL << order)
> in isolate_freepages_block(). The bogus compound_order can be any value
> because it is union with flags. Add back the MAX_PAGE_ORDER check to fix
> the warning.
> 
> Fixes: 3da0272a4c7d ("mm/compaction: correctly return failure with bogus compound_order in strict mode")
> Signed-off-by: Liu Shixin <liushixin2@...wei.com>
> ---
>  mm/compaction.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a2b16b08cbbff..384e4672998e5 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -630,7 +630,8 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
>  		if (PageCompound(page)) {
>  			const unsigned int order = compound_order(page);
>  
> -			if (blockpfn + (1UL << order) <= end_pfn) {
> +			if ((order <= MAX_PAGE_ORDER) &&
> +			    (blockpfn + (1UL << order) <= end_pfn)) {
>  				blockpfn += (1UL << order) - 1;
>  				page += (1UL << order) - 1;
>  				nr_scanned += (1UL << order) - 1;
> 
Look good to me, feel free to add
Reviewed-by: Kemeng Shi <shikemeng@...weicloud.com>