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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, William Dauchy <w.dauchy@criteo.com>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        "David S. Miller" <davem@davemloft.net>
Subject: [PATCH 5.4 003/168] net, ip_tunnel: fix interface lookup with no key
Date:   Tue, 28 Apr 2020 20:22:57 +0200
Message-Id: <20200428182232.126333532@linuxfoundation.org>
In-Reply-To: <20200428182231.704304409@linuxfoundation.org>
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From: William Dauchy <w.dauchy@criteo.com>

commit 25629fdaff2ff509dd0b3f5ff93d70a75e79e0a1 upstream.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 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
@@ -142,11 +142,8 @@ 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))
@@ -158,7 +155,6 @@ struct ip_tunnel *ip_tunnel_lookup(struc
 			cand = t;
 	}
 
-skip_key_lookup:
 	if (cand)
 		return cand;