Re: [PATCH] mm/memcg: fix NULL pointer dereference in memcg_slab_free_hook()

[wanghai (M)]

在 2021/7/28 22:26, Shakeel Butt 写道:
> On Wed, Jul 28, 2021 at 7:21 AM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> wrote:
> > On 2021/7/28 21:23, Michal Hocko wrote:
> > > On Wed 28-07-21 17:13:48, Wang Hai 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.
> > > >
> > > > So in this case, there is no need to do anything with this large
> > > > page in memcg_slab_free_hook(), just skip it.
> > > >
> > > > Fixes: 270c6a71460e ("mm: memcontrol/slab: Use helpers to access slab page's memcg_data")
> > > Are you sure that this commit is really breaking the code. Unless I have
> > Yes, we confirmed that this commit introduces the bug.
> > > missed something there shouldn't be any real change wrt. large
> > > allocations here. page_has_obj_cgroups is just a different name for what
> > > what page_objcgs is giving us.
> > maybe we could simply use page_objcgs_check to fix the issue ? we will
> > check it again.
> You will see the same crash with page_objcgs_check as well.
> .

I just test it. It won't crash.

This is the test case:

node = kmalloc_node(299999, GFP_ATOMIC | __GFP_NOWARN | __GFP_ACCOUNT, -1);
kfree_rcu(node, rcu);