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

Tim Gardner tim.gardner at canonical.com
Thu Jul 29 12:33:51 UTC 2021

From: Nicolas Dichtel <nicolas.dichtel at 6wind.com>

BugLink: https://bugs.launchpad.net/bugs/1935040

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 at 6wind.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit ff70202b2d1ad522275c6aadc8c53519b6a22c57)
Signed-off-by: Tim Gardner <tim.gardner at canonical.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 11a52f2fa35de..edd3806fe944f 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3750,7 +3750,7 @@ 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;

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