[PATCH 7.1 308/438] vxlan: use neigh_ha_snapshot() in route_shortcircuit()

7.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Eric Dumazet <[email protected]>

commit 8eca411347e1d38964f9ed2c8d3b6ab0e7e4473d upstream.

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: [email protected]
Signed-off-by: Eric Dumazet <[email protected]>
Reviewed-by: Vadim Fedorenko <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
---
 drivers/net/vxlan/vxlan_core.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2160,9 +2160,11 @@ static bool route_shortcircuit(struct ne
 	}
 
 	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);
@@ -2170,7 +2172,7 @@ static bool route_shortcircuit(struct ne
 			}
 			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;