bonding: fix PACKET_ORIGDEV regression [Linux 5.0]

This Linux kernel change "bonding: fix PACKET_ORIGDEV regression" is included in the Linux 5.0 release. This change is authored by Michal Soltys <soltys [at] ziu.info> on Mon Feb 18 17:55:28 2019 +0100. The commit for this change in Linux stable tree is 3c963a3 (patch).

bonding: fix PACKET_ORIGDEV regression

This patch fixes a subtle PACKET_ORIGDEV regression which was a side
effect of fixes introduced by:

6a9e461f6fe4 bonding: pass link-local packets to bonding master also.

... to:

b89f04c61efe bonding: deliver link-local packets with skb->dev set to link that packets arrived on

While 6a9e461f6fe4 restored pre-b89f04c61efe presence of link-local
packets on bonding masters (which is required e.g. by linux bridges
participating in spanning tree or needed for lab-like setups created
with group_fwd_mask) it also caused the originating device
information to be lost due to cloning.

Maciej ┼╗enczykowski proposed another solution that doesn't require
packet cloning and retains original device information - instead of
returning RX_HANDLER_PASS for all link-local packets it's now limited
only to packets from inactive slaves.

At the same time, packets passed to bonding masters retain correct
information about the originating device and PACKET_ORIGDEV can be used
to determine it.

This elegantly solves all issues so far:

- link-local packets that were removed from bonding masters
- LLDP daemons being forced to explicitly bind to slave interfaces
- PACKET_ORIGDEV having no effect on bond interfaces

Fixes: 6a9e461f6fe4 (bonding: pass link-local packets to bonding master also.)
Reported-by: Vincent Bernat <[email protected]>
Signed-off-by: Michal Soltys <[email protected]>
Signed-off-by: Maciej ┼╗enczykowski <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

There are 35 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/net/bonding/bond_main.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index 485462d..537c90c 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -1183,29 +1183,22 @@ static rx_handler_result_t bond_handle_frame(struct sk_buff **pskb)
        }
    }

-   /* Link-local multicast packets should be passed to the
-    * stack on the link they arrive as well as pass them to the
-    * bond-master device. These packets are mostly usable when
-    * stack receives it with the link on which they arrive
-    * (e.g. LLDP) they also must be available on master. Some of
-    * the use cases include (but are not limited to): LLDP agents
-    * that must be able to operate both on enslaved interfaces as
-    * well as on bonds themselves; linux bridges that must be able
-    * to process/pass BPDUs from attached bonds when any kind of
-    * STP version is enabled on the network.
+   /*
+    * For packets determined by bond_should_deliver_exact_match() call to
+    * be suppressed we want to make an exception for link-local packets.
+    * This is necessary for e.g. LLDP daemons to be able to monitor
+    * inactive slave links without being forced to bind to them
+    * explicitly.
+    *
+    * At the same time, packets that are passed to the bonding master
+    * (including link-local ones) can have their originating interface
+    * determined via PACKET_ORIGDEV socket option.
     */
-   if (is_link_local_ether_addr(eth_hdr(skb)->h_dest)) {
-       struct sk_buff *nskb = skb_clone(skb, GFP_ATOMIC);
-
-       if (nskb) {
-           nskb->dev = bond->dev;
-           nskb->queue_mapping = 0;
-           netif_rx(nskb);
-       }
-       return RX_HANDLER_PASS;
-   }
-   if (bond_should_deliver_exact_match(skb, slave, bond))
+   if (bond_should_deliver_exact_match(skb, slave, bond)) {
+       if (is_link_local_ether_addr(eth_hdr(skb)->h_dest))
+           return RX_HANDLER_PASS;
        return RX_HANDLER_EXACT;
+   }

    skb->dev = bond->dev;

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