From: Jakub Kicinski <kuba@kernel.org>
To: Stanislav Fomichev <sdf@google.com>
Cc: daniel@iogearbox.net, bpf@vger.kernel.org,
netdev@vger.kernel.org, Anand Parthasarathy <anpartha@meta.com>,
martin.lau@linux.dev, song@kernel.org, john.fastabend@gmail.com
Subject: Re: [PATCH bpf 1/2] bpf: pull before calling skb_postpull_rcsum()
Date: Mon, 19 Dec 2022 17:45:05 -0800 [thread overview]
Message-ID: <20221219174505.67014ea5@kernel.org> (raw)
In-Reply-To: <CAKH8qBvVTHXsgVLHuCmdFM1dnYEiDFovOFfXNq1=8igPCCO7jQ@mail.gmail.com>
On Mon, 19 Dec 2022 17:21:27 -0800 Stanislav Fomichev wrote:
> > - skb_postpull_rcsum(skb, skb->data + off, len);
> > - memmove(skb->data + len, skb->data, off);
> > + old_data = skb->data;
> > __skb_pull(skb, len);
>
> [..]
Very counter-productively trimmed ;)
> > + skb_postpull_rcsum(skb, old_data + off, len);
>
> Are you sure about the 'old_data + off' part here (for
> CHECKSUM_COMPLETE)? Shouldn't it be old_data?
AFAIU before:
old_data (aka skb->data before)
/
/ off len
V-----><--->
[ .=======xxxxx... buffer ...... ]
^
\
the xxx part is what we delete
after:
skb->data (after)
/
v
[ .yyyyy=======... buffer ...... ]
<---><----->
len off
^
\
the yyy part is technically the old values of === but now "outside"
of the valid packet data
> I'm assuming we need to negate the old parts that we've pulled?
Yes.
> Maybe safer/more correct to do the following?
>
> skb_pull_rcsum(skb, off);
This just pulls from the front, we need to skip over various L2/L3
headers thanks to off. Hopefully the diagrams help, LMK if they are
wrong.
> memmove(skb->data, skb->data-off, off);
next prev parent reply other threads:[~2022-12-20 1:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-20 0:47 [PATCH bpf 1/2] bpf: pull before calling skb_postpull_rcsum() Jakub Kicinski
2022-12-20 0:47 ` [PATCH bpf 2/2] selftests/bpf: tunnel: add sanity test for checksums Jakub Kicinski
2022-12-20 23:13 ` [PATCH bpf] selftests/bpf: Test bpf_skb_adjust_room on CHECKSUM_PARTIAL Martin KaFai Lau
2022-12-20 23:21 ` [PATCH bpf 2/2] selftests/bpf: tunnel: add sanity test for checksums Martin KaFai Lau
2022-12-20 23:36 ` Jakub Kicinski
2022-12-20 1:21 ` [PATCH bpf 1/2] bpf: pull before calling skb_postpull_rcsum() Stanislav Fomichev
2022-12-20 1:45 ` Jakub Kicinski [this message]
2022-12-20 1:55 ` Stanislav Fomichev
2022-12-21 0:20 ` patchwork-bot+netdevbpf
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