[PATCH v4 17/17] mm/sl[au]b: check if large object is valid in __ksize()

[Hyeonggon Yoo <42.hyeyoo@gmail.com>]

If address of large object is not beginning of folio or size of
the folio is too small, it must be invalid. BUG() in such cases.

Cc: Marco Elver <elver@google.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/slab_common.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/slab_common.c b/mm/slab_common.c
index 9c273a5fb0d7..98d029212682 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -984,8 +984,11 @@ size_t __ksize(const void *object)
 
 	folio = virt_to_folio(object);
 
-	if (unlikely(!folio_test_slab(folio)))
+	if (unlikely(!folio_test_slab(folio))) {
+		BUG_ON(folio_size(folio) <= KMALLOC_MAX_CACHE_SIZE);
+		BUG_ON(object != folio_address(folio));
 		return folio_size(folio);
+	}
 
 	return slab_ksize(folio_slab(folio)->slab_cache);
 }
-- 
2.32.0