From: Sven Eckelmann <sven@narfation.org>
To: Matthias Schiffer <mschiffer@universe-factory.net>
Cc: b.a.t.m.a.n@lists.open-mesh.org
Subject: Re: [B.A.T.M.A.N.] [PATCH] batman-adv: Fix skbuff rcsum on packet reroute
Date: Mon, 19 Mar 2018 14:14:04 +0100 [thread overview]
Message-ID: <6825317.Bh3rAZBzc7@bentobox> (raw)
In-Reply-To: <b50d17c8-e55f-6a05-88db-acdcc4c35732@universe-factory.net>
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On Montag, 19. März 2018 14:02:43 CET Matthias Schiffer wrote:
> Using skb_postpull_rcsum here is incorrect: As the name indicates, it is
> supposed to be used after pulling, and will thus subtract the checksum of
> the header *before* skb->data, while we are interested in the
> sizeof(*unicast_packet) bytes *after* skb->data.
Can you please explain this a little bit further. You give skb_postpull_rcsum
the start and length via parameter and it is writing the resulting csum in the
skb. It is not checking or accessing the position of skb->data [1]
/**
* skb_postpull_rcsum - update checksum for received skb after pull
* @skb: buffer to update
* @start: start of data before pull
* @len: length of data pulled
*
* After doing a pull on a received packet, you need to call this to
* update the CHECKSUM_COMPLETE checksum, or set ip_summed to
* CHECKSUM_NONE so that it can be recomputed from scratch.
*/
See also __skb_postpull_rcsum [2]:
skb->csum = csum_block_sub(skb->csum,
csum_partial(start, len, 0), off);
What about the examples I gave in my patch - for example the easy-to-read
set_eth_addr [3]?
Kind regards,
Sven
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/skbuff.h?id=c698ca5278934c0ae32297a8725ced2e27585d7f#n3070
[2] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/skbuff.h?id=c698ca5278934c0ae32297a8725ced2e27585d7f#n3058
[3] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/net/openvswitch/actions.c?id=c698ca5278934c0ae32297a8725ced2e27585d7f#n319
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next prev parent reply other threads:[~2018-03-19 13:14 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-18 12:12 [B.A.T.M.A.N.] [PATCH] batman-adv: Fix skbuff rcsum on packet reroute Sven Eckelmann
2018-03-19 13:02 ` Matthias Schiffer
2018-03-19 13:14 ` Sven Eckelmann [this message]
2018-03-19 13:19 ` Matthias Schiffer
2018-03-19 13:31 ` Sven Eckelmann
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