xfrm interface: fix packet tx through bpf_redirect()

BugLink: https://bugs.launchpad.net/bugs/1860969
With an ebpf program that redirects packets through a xfrm interface,
packets are dropped because no dst is attached to skb.

This could also be reproduced with an AF_PACKET socket, with the following
python script (xfrm1 is a xfrm 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, ('xfrm1', 0x800, 0, 0))

It was also not possible to send an ip packet through an AF_PACKET socket
because a LL header was expected. Let's remove those LL header constraints.

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
(cherry picked from commit f042365dbffea98fb8148c98c700402e8d099f02)
Signed-off-by: Kelsey Skunberg <kelsey.skunberg@canonical.com>
Acked-by: Kamal Mostafa <kamal@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/xfrm/xfrm_interface.c b/net/xfrm/xfrm_interface.c
index 2ab4859df55ac08fec69b81a2a8f1cac6585195f..6809b96714e5129036ac02ac7c3cf939a2c97ced 100644 (file)
--- a/net/xfrm/xfrm_interface.c
+++ b/net/xfrm/xfrm_interface.c
@@ -268,9 +268,6 @@ xfrmi_xmit2(struct sk_buff *skb, struct net_device *dev, struct flowi *fl)
        int err = -1;
        int mtu;
 
-       if (!dst)
-               goto tx_err_link_failure;
-
        dst_hold(dst);
        dst = xfrm_lookup_with_ifid(xi->net, dst, fl, NULL, 0, xi->p.if_id);
        if (IS_ERR(dst)) {
@@ -343,6 +340,7 @@ static netdev_tx_t xfrmi_xmit(struct sk_buff *skb, struct net_device *dev)
 {
        struct xfrm_if *xi = netdev_priv(dev);
        struct net_device_stats *stats = &xi->dev->stats;
+       struct dst_entry *dst = skb_dst(skb);
        struct flowi fl;
        int ret;
 
@@ -352,10 +350,33 @@ static netdev_tx_t xfrmi_xmit(struct sk_buff *skb, struct net_device *dev)
        case htons(ETH_P_IPV6):
                xfrm_decode_session(skb, &fl, AF_INET6);
                memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));
+               if (!dst) {
+                       fl.u.ip6.flowi6_oif = dev->ifindex;
+                       fl.u.ip6.flowi6_flags |= FLOWI_FLAG_ANYSRC;
+                       dst = ip6_route_output(dev_net(dev), NULL, &fl.u.ip6);
+                       if (dst->error) {
+                               dst_release(dst);
+                               stats->tx_carrier_errors++;
+                               goto tx_err;
+                       }
+                       skb_dst_set(skb, dst);
+               }
                break;
        case htons(ETH_P_IP):
                xfrm_decode_session(skb, &fl, AF_INET);
                memset(IPCB(skb), 0, sizeof(*IPCB(skb)));
+               if (!dst) {
+                       struct rtable *rt;
+
+                       fl.u.ip4.flowi4_oif = dev->ifindex;
+                       fl.u.ip4.flowi4_flags |= FLOWI_FLAG_ANYSRC;
+                       rt = __ip_route_output_key(dev_net(dev), &fl.u.ip4);
+                       if (IS_ERR(rt)) {
+                               stats->tx_carrier_errors++;
+                               goto tx_err;
+                       }
+                       skb_dst_set(skb, &rt->dst);
+               }
                break;
        default:
                goto tx_err;
@@ -563,12 +584,9 @@ static void xfrmi_dev_setup(struct net_device *dev)
 {
        dev->netdev_ops         = &xfrmi_netdev_ops;
        dev->type               = ARPHRD_NONE;
-       dev->hard_header_len    = ETH_HLEN;
-       dev->min_header_len     = ETH_HLEN;
        dev->mtu                = ETH_DATA_LEN;
        dev->min_mtu            = ETH_MIN_MTU;
-       dev->max_mtu            = ETH_DATA_LEN;
-       dev->addr_len           = ETH_ALEN;
+       dev->max_mtu            = IP_MAX_MTU;
        dev->flags              = IFF_NOARP;
        dev->needs_free_netdev  = true;
        dev->priv_destructor    = xfrmi_dev_free;