From: Eduard Zingerman <eddyz87@gmail.com>
To: Puranjay Mohan <puranjay@kernel.org>, bpf@vger.kernel.org
Cc: Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@kernel.org>,
kkd@meta.com, kernel-team@meta.com
Subject: Re: [PATCH bpf-next] selftests/bpf: fix list_del() in arena list
Date: Fri, 17 Oct 2025 11:35:02 -0700 [thread overview]
Message-ID: <42bc3b8552fa2dec468747fc3e81a6b011222b84.camel@gmail.com> (raw)
In-Reply-To: <20251017141727.51355-1-puranjay@kernel.org>
On Fri, 2025-10-17 at 14:17 +0000, Puranjay Mohan wrote:
> The __list_del fuction doesn't set the previous node's next pointer to
> the next node of the node to be deleted. It just updates the local variable
> and not the actual pointer in the previous node.
>
> The test was passing up till now because the bpf code is doing bpf_free()
> after list_del and therfore reading head->first from the userspace will
> read all zeroes. But after arena_list_del() is finished, head->first should
> point to NULL;
>
> If you remove the bpf_free() call in arena_list_del(), the test will start
> crashing because now the userpsace will read 0x100 (LIST_POISON1) in
> head->first and segfault.
I tried commenting out bpf_free() in arena_list_del() but the test
passes for me even w/o this patch. Is there a way to modify the test
case, so that logic of the list_del() is checked more thoroughly?
> Signed-off-by: Puranjay Mohan <puranjay@kernel.org>
[...]
next prev parent reply other threads:[~2025-10-17 18:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-10-17 14:17 [PATCH bpf-next] selftests/bpf: fix list_del() in arena list Puranjay Mohan
2025-10-17 16:31 ` Yonghong Song
2025-10-17 18:35 ` Eduard Zingerman [this message]
2025-10-17 19:09 ` Puranjay Mohan
2025-10-17 19:30 ` Yonghong Song
2025-10-17 19:55 ` Eduard Zingerman
2025-10-17 18:41 ` Alexei Starovoitov
2025-10-17 19:18 ` Puranjay Mohan
2025-10-17 21:11 ` Alexei Starovoitov
2025-10-19 2:30 ` patchwork-bot+netdevbpf
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