netdev - [PATCH net] dev_forward_skb: do not scrub skb mark within the same name space

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Message-Id: <20210624080505.21628-1-nicolas.dichtel@6wind.com>
Date:   Thu, 24 Jun 2021 10:05:05 +0200
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH net] dev_forward_skb: do not scrub skb mark within the same name space

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.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---
 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;
 }
-- 
2.30.0