[PATCH] net: Keep interface binding when sending packets with ipi_ifindex = 0

["Chia-chi Yeh (葉家齊)" <chiachi@android.com>]

In IPv4, sending a packet with ipi_ifindex = 0 via an interface-bound
socket will unbind the packet to that interface. This behavior is
different from IPv6 which treats ipi6_ifindex = 0 as unspecified.
Furthermore, IPv6 does not allow sending packets to other interface
than the bound one, but I am not sure if it is necessary in IPv4. The
following patch keeps the interface binding when ipi_ifindex = 0.

Thanks,
Chia-chi

--- a/net/ipv4/ip_sockglue.c	2009-07-24 04:50:45.000000000 +0800
+++ b/net/ipv4/ip_sockglue.c	2009-07-24 04:51:09.000000000 +0800
@@ -213,7 +213,8 @@
 			if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct in_pktinfo)))
 				return -EINVAL;
 			info = (struct in_pktinfo *)CMSG_DATA(cmsg);
-			ipc->oif = info->ipi_ifindex;
+			if (info->ipi_ifindex)
+				ipc->oif = info->ipi_ifindex;
 			ipc->addr = info->ipi_spec_dst.s_addr;
 			break;
 		}