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

Wei Yang
2025-02-11T08:11:37Z

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

>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
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