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

commit d1366e7
Author: Liu Shixin <[email protected]>
Date:   Thu Jan 23 10:10:29 2025 +0800

    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]>

CVE: CVE-2025-21815
JIRA: https://issues.redhat.com/browse/RHEL-77742
Signed-off-by: Nico Pache <[email protected]>

Author: PacheNico

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;