From: William Dauchy <w.dauchy@criteo.com>
Date: Fri, 27 Mar 2020 19:56:39 +0100
Subject: net, ip_tunnel: fix interface lookup with no key
Git-commit: 25629fdaff2ff509dd0b3f5ff93d70a75e79e0a1
Patch-mainline: 5.7-rc1
References: networking-stable-20_04_02

when creating a new ipip interface with no local/remote configuration,
the lookup is done with TUNNEL_NO_KEY flag, making it impossible to
match the new interface (only possible match being fallback or metada
case interface); e.g: `ip link add tunl1 type ipip dev eth0`

To fix this case, adding a flag check before the key comparison so we
permit to match an interface with no local/remote config; it also avoids
breaking possible userland tools relying on TUNNEL_NO_KEY flag and
uninitialised key.

context being on my side, I'm creating an extra ipip interface attached
to the physical one, and moving it to a dedicated namespace.

Fixes: c54419321455 ("GRE: Refactor GRE tunneling code.")
Signed-off-by: William Dauchy <w.dauchy@criteo.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
---
 net/ipv4/ip_tunnel.c |    6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/net/ipv4/ip_tunnel.c
+++ b/net/ipv4/ip_tunnel.c
@@ -155,11 +155,8 @@ struct ip_tunnel *ip_tunnel_lookup(struc
 			cand = t;
 	}
 
-	if (flags & TUNNEL_NO_KEY)
-		goto skip_key_lookup;
-
 	hlist_for_each_entry_rcu(t, head, hash_node) {
-		if (t->parms.i_key != key ||
+		if ((!(flags & TUNNEL_NO_KEY) && t->parms.i_key != key) ||
 		    t->parms.iph.saddr != 0 ||
 		    t->parms.iph.daddr != 0 ||
 		    !(t->dev->flags & IFF_UP))
@@ -171,7 +168,6 @@ struct ip_tunnel *ip_tunnel_lookup(struc
 			cand = t;
 	}
 
-skip_key_lookup:
 	if (cand)
 		return cand;