mm/compaction: fix UBSAN shift-out-of-bounds warning

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.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: 3da0272 ("mm/compaction: correctly return failure with bogus compound_order in strict mode")
Signed-off-by: Liu Shixin <[email protected]>
Reviewed-by: Kemeng Shi <[email protected]>
Acked-by: David Hildenbrand <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: Baolin Wang <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Nanyong Sun <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Liu Shixin

mm/compaction.c

@@ -631,7 +631,8 @@ 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;