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Message-ID: <YuFPKDx90+R3Qc6v@dhcp22.suse.cz>
Date: Wed, 27 Jul 2022 16:43:52 +0200
From: Michal Hocko <mhocko@...e.com>
To: tujinjiang@...edance.com
Cc: akpm@...ux-foundation.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Yang Shi <shy828301@...il.com>
Subject: Re: [PATCH] vmscan: fix potential arbitrary pointer passed to kfree
in unregister_shrinker
[Cc Yang Shi]
On Wed 27-07-22 17:07:00, tujinjiang@...edance.com wrote:
> From: Jinjiang Tu <tujinjiang@...edance.com>
>
> when shrinker is registered with SHRINKER_MEMCG_AWARE flag,
> register_shrinker will not initialize shrinker->nr_deferred,
> but the pointer will be passed to kfree in unregister_shrinker
> when the shrinker is unregistered. This leads to kernel crash
> when the shrinker object is dynamically allocated.
Is this a real life problem? I thought shrinkers were pre-zeroed
already. Not that we should be relying on that but it would be good to
mention whether this is a code fortification or something that we should
be really worried about.
> To fix it, this patch initialize shrinker->nr_deferred at the
> beginning of prealloc_shrinker.
It would be great to add
Fixes: 476b30a0949a ("mm: vmscan: don't need allocate shrinker->nr_deferred for memcg aware shrinkers")
> Signed-off-by: Jinjiang Tu <tujinjiang@...edance.com>
> ---
> mm/vmscan.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index f7d9a683e3a7..06ab5a398971 100644
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -613,6 +613,7 @@ int prealloc_shrinker(struct shrinker *shrinker)
> unsigned int size;
> int err;
>
> + shrinker->nr_deferred = NULL;
> if (shrinker->flags & SHRINKER_MEMCG_AWARE) {
> err = prealloc_memcg_shrinker(shrinker);
> if (err != -ENOSYS)
You should be able to move it under SHRINKER_MEMCG_AWARE branch, no?
--
Michal Hocko
SUSE Labs
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