netdev - [PATCH ipsec v2 1/2] vti[6]: fix packet tx through bpf

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Date:   Thu,  9 Jan 2020 14:35:42 +0100
From:   Nicolas Dichtel <nicolas.dichtel@...nd.com>
To:     steffen.klassert@...unet.com, davem@...emloft.net
Cc:     netdev@...r.kernel.org, Nicolas Dichtel <nicolas.dichtel@...nd.com>
Subject: [PATCH ipsec v2 1/2] vti[6]: fix packet tx through bpf_redirect()

With an ebpf program that redirects packets through a vti[6] interface,
the packets are dropped because no dst is attached.

This could also be reproduced with an AF_PACKET socket, with the following
python script (vti1 is an ip_vti interface):

 import socket
 send_s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, 0)
 # scapy
 # p = IP(src='10.100.0.2', dst='10.200.0.1')/ICMP(type='echo-request')
 # raw(p)
 req = b'E\x00\x00\x1c\x00\x01\x00\x00@\x01e\xb2\nd\x00\x02\n\xc8\x00\x01\x08\x00\xf7\xff\x00\x00\x00\x00'
 send_s.sendto(req, ('vti1', 0x800, 0, 0))

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@...nd.com>
---
 net/ipv4/ip_vti.c  | 11 +++++++++--
 net/ipv6/ip6_vti.c | 11 +++++++++--
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/net/ipv4/ip_vti.c b/net/ipv4/ip_vti.c
index e90b600c7a25..085d7aea82e7 100644
--- a/net/ipv4/ip_vti.c
+++ b/net/ipv4/ip_vti.c
@@ -187,8 +187,15 @@ static netdev_tx_t vti_xmit(struct sk_buff *skb, struct net_device *dev,
 	int mtu;
 
 	if (!dst) {
-		dev->stats.tx_carrier_errors++;
-		goto tx_error_icmp;
+		struct rtable *rt = __ip_route_output_key(dev_net(dev),
+							  &fl->u.ip4);
+
+		if (IS_ERR(rt)) {
+			dev->stats.tx_carrier_errors++;
+			goto tx_error_icmp;
+		}
+		dst = &rt->dst;
+		skb_dst_set(skb, dst);
 	}
 
 	dst_hold(dst);
diff --git a/net/ipv6/ip6_vti.c b/net/ipv6/ip6_vti.c
index 6f08b760c2a7..a6609803e8b1 100644
--- a/net/ipv6/ip6_vti.c
+++ b/net/ipv6/ip6_vti.c
@@ -449,8 +449,15 @@ vti6_xmit(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
 	int err = -1;
 	int mtu;
 
-	if (!dst)
-		goto tx_err_link_failure;
+	if (!dst) {
+		dst = ip6_route_output(dev_net(dev), NULL, &fl->u.ip6);
+		if (dst->error) {
+			dst_release(dst);
+			dst = NULL;
+			goto tx_err_link_failure;
+		}
+		skb_dst_set(skb, dst);
+	}
 
 	dst_hold(dst);
 	dst = xfrm_lookup(t->net, dst, fl, NULL, 0);
-- 
2.24.0