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

[Kemeng Shi]

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@xxxxxxxxxx>
> ---
>  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@xxxxxxxxxxxxxxx>