[PATCH 5.17 0006/1126] mm: kfence: fix missing objcg housekeeping for SLAB

[Greg Kroah-Hartman]

From: Muchun Song <songmuchun@xxxxxxxxxxxxx>

commit ae085d7f9365de7da27ab5c0d16b12d51ea7fca9 upstream.

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.

Link: https://lore.kernel.org/all/000000000000cabcb505dae9e577@xxxxxxxxxx/ [1]
Reported-by: syzbot+f8c45ccc7d5d45fc5965@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 mm/slab.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3421,6 +3421,7 @@ static __always_inline void __cache_free
 
 	if (is_kfence_address(objp)) {
 		kmemleak_free_recursive(objp, cachep->flags);
+		memcg_slab_free_hook(cachep, &objp, 1);
 		__kfence_free(objp);
 		return;
 	}