[PATCH net 3/5] vxlan: use neigh_ha_snapshot() in route_shortcircuit()

[Eric Dumazet <edumazet@google.com>]

The neighbour hardware address n->ha can be updated asynchronously by the
neighbour subsystem, protected by n->ha_lock seqlock. Reading n->ha without
holding the seqlock loop can lead to torn reads or reading a partially updated
MAC address.

Use neigh_ha_snapshot() in route_shortcircuit() to safely copy n->ha under
read_seqbegin()/read_seqretry() lock protection before using it.

Note that arp_reduce() and neigh_reduce() seem to have the same issue
left for future patches.

Fixes: e4f67addf158 ("add DOVE extensions for VXLAN")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 drivers/net/vxlan/vxlan_core.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index fb4a706cd5786d1937b1922acced31ffdb187c2f..10dd19eec09e266197ee51330a652f4e76c9643a 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2159,9 +2159,11 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb)
 	}
 
 	if (n) {
+		u8 haddr[ETH_ALEN];
 		bool diff;
 
-		diff = !ether_addr_equal(eth_hdr(skb)->h_dest, n->ha);
+		neigh_ha_snapshot(haddr, n, dev);
+		diff = !ether_addr_equal_unaligned(eth_hdr(skb)->h_dest, haddr);
 		if (diff) {
 			if (skb_cow_head(skb, 0)) {
 				neigh_release(n);
@@ -2169,7 +2171,7 @@ static bool route_shortcircuit(struct net_device *dev, struct sk_buff *skb)
 			}
 			memcpy(eth_hdr(skb)->h_source, eth_hdr(skb)->h_dest,
 				dev->addr_len);
-			memcpy(eth_hdr(skb)->h_dest, n->ha, dev->addr_len);
+			memcpy(eth_hdr(skb)->h_dest, haddr, dev->addr_len);
 		}
 		neigh_release(n);
 		return diff;
-- 
2.55.0.229.g6434b31f56-goog