Messages in this thread | | | From | Yang Shi <> | Date | Wed, 27 Jul 2022 08:50:16 -0700 | Subject | Re: [PATCH] vmscan: fix potential arbitrary pointer passed to kfree in unregister_shrinker |
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On Wed, Jul 27, 2022 at 7:43 AM Michal Hocko <mhocko@suse.com> wrote: > > [Cc Yang Shi]
Thanks, Michal.
> 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.
Yes, all memcg aware shrinkers are actually pre-zeroed. The fs shrinkers (embedded in super_block) are allocated by kzalloc, all other shrinkers are static declared. So I don't think it will cause any crash in real life.
> > > 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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