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09 April 2024, 21:14:05 UTC
Revision 3a93b00269b1fb762b2c9f98ab67a6ed3a333dda authored by Gray Liang on 23 October 2023, 03:13:25 UTC, committed by Julian Wiedmann on 01 December 2023, 16:20:14 UTC 
bpf: work around scrubbing of skb->mark during veth transition
 
Previously we set skb->mark in from_host@cilium_host, expect the mark
to remain unchanged after kernel transmits skb from cilium_host to
cilium_net. The skb->mark is for instance used to transport
IPsec-related information.

However, as of 2023-10-19, kernel 5.10 still misses the backport patch[1]
to fix a bug in skb_scrub_packet() which clears skb->mark for veth_xmit even if the
veth pair is under the same netns:
https://elixir.bootlin.com/linux/v5.10.198/source/include/linux/netdevice.h#L3975

To avoid hitting this issue, this patch sets metadata in skb->cb to
survive skb_scrub_packet(), then to_host@cilium_net can retrieve this
info and set proper mark.

Only from_host bpf is setting cb, while from_lxc bpf is still using mark.

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ff70202b2d1a ("dev_forward_skb: do not scrub skb mark within the same name space")

Signed-off-by: Zhichuan Liang <gray.liang@isovalent.com>
1 parent e78ff16
History
Tip revision: 3a93b00269b1fb762b2c9f98ab67a6ed3a333dda authored by Gray Liang on 23 October 2023, 03:13:25 UTC
bpf: work around scrubbing of skb->mark during veth transition
Tip revision: 3a93b00
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