Re: [PATCH net] dev_forward_skb: do not scrub skb mark within the same name space
From: Eyal Birger <hidden>
Date: 2021-06-24 12:16:59
Hi Nicholas, On 24/06/2021 11:05, Nicolas Dichtel wrote:
The goal is to keep the mark during a bpf_redirect(), like it is done for
legacy encapsulation / decapsulation, when there is no x-netns.
This was initially done in commit 213dd74aee76 ("skbuff: Do not scrub skb
mark within the same name space").
When the call to skb_scrub_packet() was added in dev_forward_skb() (commit
8b27f27797ca ("skb: allow skb_scrub_packet() to be used by tunnels")), the
second argument (xnet) was set to true to force a call to skb_orphan(). At
this time, the mark was always cleanned up by skb_scrub_packet(), whatever
xnet value was.
This call to skb_orphan() was removed later in commit
9c4c325252c5 ("skbuff: preserve sock reference when scrubbing the skb.").
But this 'true' stayed here without any real reason.
Let's correctly set xnet in ____dev_forward_skb(), this function has access
to the previous interface and to the new interface.This change was suggested in the past [1] and I think one of the main concerns was breaking existing callers which assume the mark would be cleared [2]. Personally, I think the suggestion made in [3] adding a flag to bpf_redirect() makes a lot of sense for this use case. Eyal. [1] https://lore.kernel.org/netdev/1520953642-8145-1-git-send-email-liran.alon@oracle.com/ (local) [2] https://lore.kernel.org/netdev/20180315112150.58586758@halley/ (local) [3] https://lore.kernel.org/netdev/cd0b73e3-2cde-1442-4312-566c69571e8a@iogearbox.net/ (local)
quoted hunk ↗ jump to hunk
Signed-off-by: Nicolas Dichtel <redacted> --- include/linux/netdevice.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h index 5cbc950b34df..5ab2d1917ca1 100644 --- a/include/linux/netdevice.h +++ b/include/linux/netdevice.h@@ -4114,7 +4114,7 @@ static __always_inline int ____dev_forward_skb(struct net_device *dev, return NET_RX_DROP; } - skb_scrub_packet(skb, true); + skb_scrub_packet(skb, !net_eq(dev_net(dev), dev_net(skb->dev))); skb->priority = 0; return 0; }