Re: [PATCH 0/3] may miss to set node dead on destroy

Liam R. Howlett
2025-02-11T15:29:17Z

* Wei Yang <richard.weiyang@gmail.com> [250211 03:11]:
> On Mon, Feb 10, 2025 at 09:31:28AM -0500, Liam R. Howlett wrote:
> >* Wei Yang <richard.weiyang@gmail.com> [250207 20:26]:
> >
> >The subject of this patch set makes the issue sound much more sever than
> >it is. It currently sounds like a memory leak or a UAF, which isn't the
> >case.
> >
>
> Not intend to exaggerate the impact.
>
> Is this one would be better?
>
> maple_tree: make sure each node is dead on destroy

Not really, you are fixing two nodes, one isn't even to do with the
destry/dead node. You are also not making sure each node is dead, but
fixing an issue with the leaf node.

maple_tree: Fix the replacement of a root leaf node ?

>
> >The root node may remain usable for the duration of the rcu window if
> >it's a leaf node. The impact is pretty minor - you may see the old data
> >on calls that happen in the same rcu window - which is the case anyways.
> >
> >You should also say maple_tree: in the subject since this is
> >going to linux-mm. Not a really big deal since each patch in the series
> >specifies the maple tree.
> >
>
> Thanks, will add it in next version.
>
> >> Per my understanding, on destroy we should set each node dead. But current
> >> code miss this when the maple tree has only the root node.
> >>
> >> The reason is mt_destroy_walk() leverage mte_destroy_descend() to set
> >> node dead, but this is skipped since the only root node is a leaf.
> >>
> >> Patch 1 fixes this.
> >>
> >> When adding a test case, I found we always get the new value even we leave the
> >> old root node not dead. It turns out we always re-walk the tree in mas_walk().
> >> It looks like a typo on the status check of mas_walk().
> >>
> >> Patch 2 fixes this.
> >>
> >> Patch 3 add a test case to assert retrieving new value when overwriting the
> >> whole range to a tree with only root node
> >>
> >> Wei Yang (3):
> >> maple_tree: may miss to set node dead on destroy
> >> maple_tree: restart walk on correct status
> >> maple_tree: assert retrieving new value on a tree with only root node
> >>
> >> lib/maple_tree.c | 4 +++-
> >> tools/testing/radix-tree/maple.c | 24 ++++++++++++++++++++++++
> >> 2 files changed, 27 insertions(+), 1 deletion(-)
> >>
> >> --
> >> 2.34.1
> >>
>
> --
> Wei Yang
> Help you, Help me