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

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Message-ID: <ZxmnZWjSRVHgtbGZ@localhost.localdomain>
Date: Thu, 24 Oct 2024 10:48:21 +0900
From: Byeonguk Jeong <jungbu2855@...il.com>
To: Hou Tao <houtao@...weicloud.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()

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.