From: "D. Wythe" <alibuda@linux.alibaba.com>
To: pablo@netfilter.org, kadlec@netfilter.org, fw@strlen.de,
coreteam@netfilter.org, pabeni@redhat.com, ast@kernel.org,
netfilter-devel@vger.kernel.org, bpf@vger.kernel.org
Subject: Can netfilter-ebpf modify packets ？
Date: Mon, 18 Dec 2023 14:26:43 +0800 [thread overview]
Message-ID: <e616c2ac-e68b-3814-eac3-304e49eb39b8@linux.alibaba.com> (raw)
Hello everyone,
I've noticed that it's not possible to modify packets via netfilter-ebpf
right now. I'm curious if this is by design.
Currently, I've observed some issues, such as:
1. The dynptr obtained through bpf_dynptr_from_skb in the netfilter-ebpf
prog is read-only.
2. In addition to modification, applications may also need to delete or
append some data in the skb, which dynptr_write cannot meet.
3. Modifying packets involves recalculating csum, or updating
transparent header, etc.
4. The BPF_PROG_TYPE_SCHED_ACT provides a large number of helpers that
can meet various packet modification scenarios. However, due to arg_type
type checks(ARG_PTR_TO_CTX), we cannot use them directly in netfilter yet.
Looking forward to any feedback.
Best wishes,
D. Wythe
reply other threads:[~2023-12-18 6:26 UTC|newest]
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