When we do IPsec offloading, we need a fallback for
packets that were targeted to be IPsec offloaded but
rerouted to a device that does not support IPsec offload.
For that we add a function that checks the offloading
features of the sending device and and flags the
requirement of a fallback before it calls the IPsec
output function. The IPsec output function adds the IPsec
trailer and does encryption if needed.

Signed-off-by: Steffen Klassert <steffen.klass...@secunet.com>
---
 include/net/xfrm.h     |  6 ++++++
 net/core/dev.c         |  3 +++
 net/xfrm/xfrm_device.c | 29 +++++++++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/include/net/xfrm.h b/include/net/xfrm.h
index 17603bf..6793a30c 100644
--- a/include/net/xfrm.h
+++ b/include/net/xfrm.h
@@ -1862,6 +1862,7 @@ static inline struct xfrm_offload *xfrm_offload(struct 
sk_buff *skb)
 
 #ifdef CONFIG_XFRM_OFFLOAD
 void __net_init xfrm_dev_init(void);
+int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features);
 int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
                       struct xfrm_user_offload *xuo);
 bool xfrm_dev_offload_ok(struct sk_buff *skb, struct xfrm_state *x);
@@ -1890,6 +1891,11 @@ static inline void __net_init xfrm_dev_init(void)
 {
 }
 
+static inline int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t 
features)
+{
+       return 0;
+}
+
 static inline int xfrm_dev_state_add(struct net *net, struct xfrm_state *x, 
struct xfrm_user_offload *xuo)
 {
        return 0;
diff --git a/net/core/dev.c b/net/core/dev.c
index ef9fe60e..5f0a864 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -2972,6 +2972,9 @@ static struct sk_buff *validate_xmit_skb(struct sk_buff 
*skb, struct net_device
                    __skb_linearize(skb))
                        goto out_kfree_skb;
 
+               if (validate_xmit_xfrm(skb, features))
+                       goto out_kfree_skb;
+
                /* If packet is not checksummed and device does not
                 * support checksumming for this protocol, complete
                 * checksumming here.
diff --git a/net/xfrm/xfrm_device.c b/net/xfrm/xfrm_device.c
index 9bac2ba..8ec8a3f 100644
--- a/net/xfrm/xfrm_device.c
+++ b/net/xfrm/xfrm_device.c
@@ -22,6 +22,35 @@
 #include <net/xfrm.h>
 #include <linux/notifier.h>
 
+int validate_xmit_xfrm(struct sk_buff *skb, netdev_features_t features)
+{
+       int err;
+       struct xfrm_state *x;
+       struct xfrm_offload *xo = xfrm_offload(skb);
+
+       if (skb_is_gso(skb))
+               return 0;
+
+       if (xo) {
+               x = skb->sp->xvec[skb->sp->len - 1];
+               if (xo->flags & XFRM_GRO || x->xso.flags & XFRM_OFFLOAD_INBOUND)
+                       return 0;
+
+               x->outer_mode->xmit(x, skb);
+
+               err = x->type_offload->xmit(x, skb, features);
+               if (err) {
+                       XFRM_INC_STATS(xs_net(x), 
LINUX_MIB_XFRMOUTSTATEPROTOERROR);
+                       return err;
+               }
+
+               skb_push(skb, skb->data - skb_mac_header(skb));
+       }
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(validate_xmit_xfrm);
+
 int xfrm_dev_state_add(struct net *net, struct xfrm_state *x,
                       struct xfrm_user_offload *xuo)
 {
-- 
2.7.4

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