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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com,
        Muchun Song <songmuchun@bytedance.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Marco Elver <elver@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 5.16 0006/1017] mm: kfence: fix missing objcg housekeeping for SLAB
Date:   Tue,  5 Apr 2022 09:15:19 +0200
Message-Id: <20220405070354.358398291@linuxfoundation.org>
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From: Muchun Song <songmuchun@bytedance.com>

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@google.com/ [1]
Reported-by: syzbot+f8c45ccc7d5d45fc5965@syzkaller.appspotmail.com
Fixes: d3fb45f370d9 ("mm, kfence: insert KFENCE hooks for SLAB")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Marco Elver <elver@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 mm/slab.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -3429,6 +3429,7 @@ 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;
 	}