linux-kernel - Re: [PATCH v2] mm/memcg: fix NULL pointer dereference in memcg_slab_free

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Date:   Wed, 28 Jul 2021 08:14:50 -0700
From:   Shakeel Butt <shakeelb@...gle.com>
To:     Wang Hai <wanghai38@...wei.com>
Cc:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Roman Gushchin <guro@...com>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()

On Wed, Jul 28, 2021 at 7:57 AM Wang Hai <wanghai38@...wei.com> wrote:
>
> When I use kfree_rcu() to free a large memory allocated by
> kmalloc_node(), the following dump occurs.
>
> BUG: kernel NULL pointer dereference, address: 0000000000000020
> [...]
> Oops: 0000 [#1] SMP
> [...]
> Workqueue: events kfree_rcu_work
> RIP: 0010:__obj_to_index include/linux/slub_def.h:182 [inline]
> RIP: 0010:obj_to_index include/linux/slub_def.h:191 [inline]
> RIP: 0010:memcg_slab_free_hook+0x120/0x260 mm/slab.h:363
> [...]
> Call Trace:
>  kmem_cache_free_bulk+0x58/0x630 mm/slub.c:3293
>  kfree_bulk include/linux/slab.h:413 [inline]
>  kfree_rcu_work+0x1ab/0x200 kernel/rcu/tree.c:3300
>  process_one_work+0x207/0x530 kernel/workqueue.c:2276
>  worker_thread+0x320/0x610 kernel/workqueue.c:2422
>  kthread+0x13d/0x160 kernel/kthread.c:313
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>
> When kmalloc_node() a large memory, page is allocated, not slab,
> so when freeing memory via kfree_rcu(), this large memory should not
> be used by memcg_slab_free_hook(), because memcg_slab_free_hook() is
> is used for slab.
>
> Using page_objcgs_check() instead of page_objcgs() in
> memcg_slab_free_hook() to fix this bug.
>
> Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data")
> Signed-off-by: Wang Hai <wanghai38@...wei.com>

Reviewed-by: Shakeel Butt <shakeelb@...gle.com>