Messages in this thread | | | Date | Wed, 27 Jul 2022 16:43:52 +0200 | From | Michal Hocko <> | Subject | Re: [PATCH] vmscan: fix potential arbitrary pointer passed to kfree in unregister_shrinker |
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[Cc Yang Shi] On Wed 27-07-22 17:07:00, tujinjiang@bytedance.com wrote: > From: Jinjiang Tu <tujinjiang@bytedance.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@bytedance.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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