Message-ID: <31773.1640033306@famine>
Date:   Mon, 20 Dec 2021 12:48:26 -0800
From:   Jay Vosburgh <jay.vosburgh@...onical.com>
To:     Sun Shouxin <sunshouxin@...natelecom.cn>
cc:     vfalico@...il.com, andy@...yhouse.net, davem@...emloft.net,
        kuba@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, huyd12@...natelecom.cn
Subject: Re: [PATCH v4] net: bonding: Add support for IPV6 ns/na to balance-alb mode

Sun Shouxin <sunshouxin@...natelecom.cn> wrote:

>Since ipv6 neighbor solicitation and advertisement messages
>isn't handled gracefully in bonding6 driver, we can see packet
>drop due to inconsistency bewteen mac address in the option
>message and source MAC .
>
>Another examples is ipv6 neighbor solicitation and advertisement
>messages from VM via tap attached to host brighe, the src mac
>mighe be changed through balance-alb mode, but it is not synced
>with Link-layer address in the option message.
>
>The patch implements bond6's tx handle for ipv6 neighbor
>solicitation and advertisement messages.
>
>                        Border-Leaf
>                        /        \
>                       /          \
>                    Tunnel1    Tunnel2
>                     /              \
>                    /                \
>                  Leaf-1--Tunnel3--Leaf-2
>                    \                /
>                     \              /
>                      \            /
>                       \          /
>                       NIC1    NIC2
>                         \      /
>                          server
>
>We can see in our lab the Border-Leaf receives occasionally
>a NA packet which is assigned to NIC1 mac in ND/NS option
>message, but actaully send out via NIC2 mac due to tx-alb,
>as a result, it will cause inconsistency between MAC table
>and ND Table in Border-Leaf, i.e, NIC1 = Tunnel2 in ND table
>and  NIC1 = Tunnel1 in mac table.
>
>And then, Border-Leaf starts to forward packet destinated
>to the Server, it will only check the ND table entry in some
>switch to encapsulate the destination MAC of the message as
>NIC1 MAC, and then send it out from Tunnel2 by ND table.
>Then, Leaf-2 receives the packet, it notices the destination
>MAC of message is NIC1 MAC and should forword it to Tunne1
>by Tunnel3.

	Should the above state "forward it to Leaf-1 by Tunnel3", not
"to Tunnel1"?  Presumably Leaf-1 would then forward a packet with NIC1
MAC destination directly to NIC1.  You mention VXLAN split horizon
below, but I'm unclear on exactly why that results in a failure to
forward vs selecting a suboptimal path.

	My overall concern here is that this is a complex solution for a
very specific configuration, and I'm not sure exactly which piece is
doing something wrong (i.e., is Border-Leaf correct in selecting
Tunnel2?).

	And, further, this topology is outside the scope of what the tlb
/ alb modes were designed around (which was interfacing with a single
switch, not a distributed switch topology as shown above); alb's inbound
load balancing in particular wasn't set up for IPv6 (it only modifies
ARPs to assign peers to specific bonding interfaces).  That's not to say
that we can't fix up the IPv6 support, but I don't want to eventually
have a collection of band-aids for specific corner cases.

	Also, on thinking about it, I'm unsure why the tlb mode would
not exhibit the same issue, since you're not altering the alb inbound
load balancer (the "tailored ARP per peer" logic), just the regular
transmit side, which is largely the same for tlb.  Have you tested
balance-tlb mode?

	Lastly, Eric's question about not altering the original skb
isn't explictly addressed that I can see (although it seems Eric was
concerned about received packets, and this is modifying packets being
transmitted).  The code looks like it shouldn't modify NS/NA packets
that are being forwarded through the bond (the bond_slave_has_mac_rx
test), but is it possible for a locally originating NS/NA to be a clone?

	-J

>However, this traffic forward will be failure due to split
>horizon of VxLAN tunnels.
>
>Suggested-by: Hu Yadi <huyd12@...natelecom.cn>
>Reported-by: kernel test robot <lkp@...el.com>
>Signed-off-by: Sun Shouxin <sunshouxin@...natelecom.cn>
>---
> drivers/net/bonding/bond_alb.c | 132 +++++++++++++++++++++++++++++++++
> 1 file changed, 132 insertions(+)
>
>diff --git a/drivers/net/bonding/bond_alb.c b/drivers/net/bonding/bond_alb.c
>index 533e476988f2..e8d6d1f2f540 100644
>--- a/drivers/net/bonding/bond_alb.c
>+++ b/drivers/net/bonding/bond_alb.c
>@@ -22,6 +22,7 @@
> #include <asm/byteorder.h>
> #include <net/bonding.h>
> #include <net/bond_alb.h>
>+#include <net/ndisc.h>
> 
> static const u8 mac_v6_allmcast[ETH_ALEN + 2] __long_aligned = {
> 	0x33, 0x33, 0x00, 0x00, 0x00, 0x01
>@@ -1269,6 +1270,120 @@ static int alb_set_mac_address(struct bonding *bond, void *addr)
> 	return res;
> }
> 
>+/*determine if the packet is NA or NS*/
>+static bool alb_determine_nd(struct icmp6hdr *hdr)
>+{
>+	if (hdr->icmp6_type == NDISC_NEIGHBOUR_ADVERTISEMENT ||
>+	    hdr->icmp6_type == NDISC_NEIGHBOUR_SOLICITATION) {
>+		return true;
>+	}
>+
>+	return false;
>+}
>+
>+static void alb_change_nd_option(struct sk_buff *skb, void *data)
>+{
>+	struct nd_msg *msg = (struct nd_msg *)skb_transport_header(skb);
>+	struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)msg->opt;
>+	struct net_device *dev = skb->dev;
>+	struct icmp6hdr *icmp6h = icmp6_hdr(skb);
>+	struct ipv6hdr *ip6hdr = ipv6_hdr(skb);
>+	u8 *lladdr = NULL;
>+	u32 ndoptlen = skb_tail_pointer(skb) - (skb_transport_header(skb) +
>+				offsetof(struct nd_msg, opt));
>+
>+	while (ndoptlen) {
>+		int l;
>+
>+		switch (nd_opt->nd_opt_type) {
>+		case ND_OPT_SOURCE_LL_ADDR:
>+		case ND_OPT_TARGET_LL_ADDR:
>+			lladdr = ndisc_opt_addr_data(nd_opt, dev);
>+			break;
>+
>+		default:
>+			lladdr = NULL;
>+			break;
>+		}
>+
>+		l = nd_opt->nd_opt_len << 3;
>+
>+		if (ndoptlen < l || l == 0)
>+			return;
>+
>+		if (lladdr) {
>+			memcpy(lladdr, data, dev->addr_len);
>+			icmp6h->icmp6_cksum = 0;
>+
>+			icmp6h->icmp6_cksum = csum_ipv6_magic(&ip6hdr->saddr,
>+							      &ip6hdr->daddr,
>+						ntohs(ip6hdr->payload_len),
>+						IPPROTO_ICMPV6,
>+						csum_partial(icmp6h,
>+							     ntohs(ip6hdr->payload_len), 0));
>+			return;
>+		}
>+		ndoptlen -= l;
>+		nd_opt = ((void *)nd_opt) + l;
>+	}
>+}
>+
>+static u8 *alb_get_lladdr(struct sk_buff *skb)
>+{
>+	struct nd_msg *msg = (struct nd_msg *)skb_transport_header(skb);
>+	struct nd_opt_hdr *nd_opt = (struct nd_opt_hdr *)msg->opt;
>+	struct net_device *dev = skb->dev;
>+	u8 *lladdr = NULL;
>+	u32 ndoptlen = skb_tail_pointer(skb) - (skb_transport_header(skb) +
>+				offsetof(struct nd_msg, opt));
>+
>+	while (ndoptlen) {
>+		int l;
>+
>+		switch (nd_opt->nd_opt_type) {
>+		case ND_OPT_SOURCE_LL_ADDR:
>+		case ND_OPT_TARGET_LL_ADDR:
>+			lladdr = ndisc_opt_addr_data(nd_opt, dev);
>+			break;
>+
>+		default:
>+			break;
>+		}
>+
>+		l = nd_opt->nd_opt_len << 3;
>+
>+		if (ndoptlen < l || l == 0)
>+			return NULL;
>+
>+		if (lladdr)
>+			return lladdr;
>+
>+		ndoptlen -= l;
>+		nd_opt = ((void *)nd_opt) + l;
>+	}
>+
>+	return lladdr;
>+}
>+
>+static void alb_set_nd_option(struct sk_buff *skb, struct bonding *bond,
>+			      struct slave *tx_slave)
>+{
>+	struct ipv6hdr *ip6hdr;
>+	struct icmp6hdr *hdr;
>+
>+	if (skb->protocol == htons(ETH_P_IPV6)) {
>+		if (tx_slave && tx_slave !=
>+		    rcu_access_pointer(bond->curr_active_slave)) {
>+			ip6hdr = ipv6_hdr(skb);
>+			if (ip6hdr->nexthdr == IPPROTO_ICMPV6) {
>+				hdr = icmp6_hdr(skb);
>+				if (alb_determine_nd(hdr))
>+					alb_change_nd_option(skb, tx_slave->dev->dev_addr);
>+			}
>+		}
>+	}
>+}
>+
> /************************ exported alb functions ************************/
> 
> int bond_alb_initialize(struct bonding *bond, int rlb_enabled)
>@@ -1415,6 +1530,7 @@ struct slave *bond_xmit_alb_slave_get(struct bonding *bond,
> 	}
> 	case ETH_P_IPV6: {
> 		const struct ipv6hdr *ip6hdr;
>+		struct icmp6hdr *hdr;
> 
> 		/* IPv6 doesn't really use broadcast mac address, but leave
> 		 * that here just in case.
>@@ -1446,6 +1562,21 @@ struct slave *bond_xmit_alb_slave_get(struct bonding *bond,
> 			break;
> 		}
> 
>+		if (ip6hdr->nexthdr == IPPROTO_ICMPV6) {
>+			hdr = icmp6_hdr(skb);
>+			if (alb_determine_nd(hdr)) {
>+				u8 *lladdr;
>+
>+				lladdr = alb_get_lladdr(skb);
>+				if (lladdr) {
>+					if (!bond_slave_has_mac_rx(bond, lladdr)) {
>+						do_tx_balance = false;
>+						break;
>+					}
>+				}
>+			}
>+		}
>+
> 		hash_start = (char *)&ip6hdr->daddr;
> 		hash_size = sizeof(ip6hdr->daddr);
> 		break;
>@@ -1489,6 +1620,7 @@ netdev_tx_t bond_alb_xmit(struct sk_buff *skb, struct net_device *bond_dev)
> 	struct slave *tx_slave = NULL;
> 
> 	tx_slave = bond_xmit_alb_slave_get(bond, skb);
>+	alb_set_nd_option(skb, bond, tx_slave);
> 	return bond_do_alb_xmit(skb, bond, tx_slave);
> }
> 
>
>base-commit: a7904a538933c525096ca2ccde1e60d0ee62c08e
>-- 
>2.27.0
>

---
	-Jay Vosburgh, jay.vosburgh@...onical.com

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