net: original ingress device index in PKTINFO

Applications such as OSPF and BFD need the original ingress device not
the VRF device; the latter can be derived from the former. To that end
add the skb_iif to inet_skb_parm and set it in ipv4 code after clearing
the skb control buffer similar to IPv6. From there the pktinfo can just
pull it from cb with the PKTINFO_SKB_CB cast.

The previous patch moving the skb->dev change to L3 means nothing else
is needed for IPv6; it just works.

Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

3 files changed, 8 insertions, 1 deletions

diff --git a/include/net/ip.h b/include/net/ip.h
index 247ac82e9cf2..37165fba3741 100644
--- a/include/net/ip.h
+++ b/include/net/ip.h
@@ -36,6 +36,7 @@
 struct sock;
 
 struct inet_skb_parm {
+        int                     iif;
         struct ip_options       opt;            /* Compiled IP options          */
         unsigned char           flags;
 
diff --git a/net/ipv4/ip_input.c b/net/ipv4/ip_input.c
index 37375eedeef9..4b351af3e67b 100644
--- a/net/ipv4/ip_input.c
+++ b/net/ipv4/ip_input.c
@@ -478,6 +478,7 @@ int ip_rcv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt,
 
         /* Remove any debris in the socket control block */
         memset(IPCB(skb), 0, sizeof(struct inet_skb_parm));
+        IPCB(skb)->iif = skb->skb_iif;
 
         /* Must drop socket now because of tproxy. */
         skb_orphan(skb);
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
index bdb222c0c6a2..5805762d7fc7 100644
--- a/net/ipv4/ip_sockglue.c
+++ b/net/ipv4/ip_sockglue.c
@@ -1193,7 +1193,12 @@ void ipv4_pktinfo_prepare(const struct sock *sk, struct sk_buff *skb)
                        ipv6_sk_rxinfo(sk);
 
         if (prepare && skb_rtable(skb)) {
-                pktinfo->ipi_ifindex = inet_iif(skb);
+                /* skb->cb is overloaded: prior to this point it is IP{6}CB
+                 * which has interface index (iif) as the first member of the
+                 * underlying inet{6}_skb_parm struct. This code then overlays
+                 * PKTINFO_SKB_CB and in_pktinfo also has iif as the first
+                 * element so the iif is picked up from the prior IPCB
+                 */
                 pktinfo->ipi_spec_dst.s_addr = fib_compute_spec_dst(skb);
         } else {
                 pktinfo->ipi_ifindex = 0;