net: fix incorrect original ingress device index in PKTINFO

asuka2001 · davem330 · commit f0c16ba8933e · 2016-12-29T14:07:41.000-05:00
When we send a packet for our own local address on a non-loopback interface (e.g. eth0), due to the change had been introduced from commit 0b922b7 ("net: original ingress device index in PKTINFO"), the original ingress device index would be set as the loopback interface. However, the packet should be considered as if it is being arrived via the sending interface (eth0), otherwise it would break the expectation of the userspace application (e.g. the DHCPRELEASE message from dhcp_release binary would be ignored by the dnsmasq daemon, since it come from lo which is not the interface dnsmasq bind to) Fixes: 0b922b7 ("net: original ingress device index in PKTINFO") Acked-by: David Ahern <dsa@cumulusnetworks.com> Signed-off-by: Wei Zhang <asuka.com@163.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ip_sockglue.c b/net/ipv4/ip_sockglue.c
@@ -1225,8 +1225,14 @@ void ipv4_pktinfo_prepare(const struct sock *sk, struct sk_buff *skb)
 		 * 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
+		 * element so the iif is picked up from the prior IPCB. If iif
+		 * is the loopback interface, then return the sending interface
+		 * (e.g., process binds socket to eth0 for Tx which is
+		 * redirected to loopback in the rtable/dst).
 		 */
+		if (pktinfo->ipi_ifindex == LOOPBACK_IFINDEX)
+			pktinfo->ipi_ifindex = inet_iif(skb);
+
 		pktinfo->ipi_spec_dst.s_addr = fib_compute_spec_dst(skb);
 	} else {
 		pktinfo->ipi_ifindex = 0;
