[PATCH 1/2] mm: kfence: fix missing objcg housekeeping for SLAB

[Muchun Song]

The objcg is not cleared and put for kfence object when it is freed, which
could lead to memory leak for struct obj_cgroup and wrong statistics of
NR_SLAB_RECLAIMABLE_B or NR_SLAB_UNRECLAIMABLE_B.  Since the last freed
object's objcg is not cleared, mem_cgroup_from_obj() could return the wrong
memcg when this kfence object, which is not charged to any objcgs, is
reallocated to other users.  A real word issue [1] is caused by this bug.

[1] https://groups.google.com/g/syzkaller-bugs/c/BBQFy2QraoY/m/HtBd5gbyAQAJ
Reported-by: syzbot+f8c45ccc7d5d45fc5965@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
---
 mm/slab.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/slab.c b/mm/slab.c
index d9dec7a8fd79..b04e40078bdf 100644
--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3422,6 +3422,7 @@ static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
 
 	if (is_kfence_address(objp)) {
 		kmemleak_free_recursive(objp, cachep->flags);
+		memcg_slab_free_hook(cachep, &objp, 1);
 		__kfence_free(objp);
 		return;
 	}
-- 
2.11.0