linux-kernel - Re: [PATCH] bpf: Fix out-of-bounds write in trie_get_next

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Message-ID: <a7cbcc55-0913-fdcb-3100-b9f71817bfaf@huaweicloud.com>
Date: Thu, 24 Oct 2024 11:19:21 +0800
From: Hou Tao <houtao@...weicloud.com>
To: Byeonguk Jeong <jungbu2855@...il.com>
Cc: Daniel Borkmann <daniel@...earbox.net>,
 Yonghong Song <yonghong.song@...ux.dev>, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] bpf: Fix out-of-bounds write in trie_get_next_key()



On 10/24/2024 9:48 AM, Byeonguk Jeong wrote:
> Hi,
>
> On Wed, Oct 23, 2024 at 05:59:53PM +0800, Hou Tao wrote:
>> Alexei suggested adding a bpf self-test for the patch.  I think you
>> could reference the code in lpm_trie_map_batch_ops.c [1] or similar and
>> add a new file that uses bpf_map_get_next_key to demonstrate the
>> out-of-bound problem. The test can be run by ./test_maps. There is some
>> document for the procedure in [2].
>>
>> [1]:  tools/testing/selftests/bpf/map_tests/lpm_trie_map_batch_ops.c
>> [2]:
>> https://github.com/torvalds/linux/blob/master/Documentation/bpf/bpf_devel_QA.rst
> Okay, I will add a new test. Thanks for the detailed guideline.
>
>> Which procedure will return -ENOENT ? I think the element with
>> prefixlen=0 could still be found through the key with prefixlen = 0.
> I mean, BPF_MAP_GET_NEXT_KEY with .prefixlen = 0 would give us -ENOENT,
> as it follows postorder. BPF_MAP_LOOKUP_ELEM still find the element
> with prefixlen 0 through the key with prefixlen 0 as you said.

I see. But considering the element with .prefixlen = 0 is the last one
in the map, returning -ENOENT is expected.
> .