route: do not cache fib route info on local routes with oif

For local routes that require a particular output interface we do not want to cache the result. Caching the result causes incorrect behaviour when there are multiple source addresses on the interface. The end result being that if the intended recipient is waiting on that interface for the packet he won't receive it because it will be delivered on the loopback interface and the IP_PKTINFO ipi_ifindex will be set to the loopback interface as well. This can be tested by running a program such as "dhcp_release" which attempts to inject a packet on a particular interface so that it is received by another program on the same board. The receiving process should see an IP_PKTINFO ipi_ifndex value of the source interface (e.g., eth1) instead of the loopback interface (e.g., lo). The packet will still appear on the loopback interface in tcpdump but the important aspect is that the CMSG info is correct. Sample dhcp_release command line: dhcp_release eth1 192.168.204.222 02:11:33:22:44:66 Signed-off-by: Allain Legacy <[email protected]> Signed off-by: Chris Friesen <[email protected]> Reviewed-by: Julian Anastasov <[email protected]> Signed-off-by: David S. Miller <[email protected]>
hardkernel · Apr 14, 2016 · d6d5e99 · d6d5e99
1 parent 65c66af
commit d6d5e99
Showing 1 changed file with 12 additions and 0 deletions.
diff --git a/net/ipv4/route.c b/net/ipv4/route.c
@@ -2046,6 +2046,18 @@ static struct rtable *__mkroute_output(const struct fib_result *res,
 		 */
 		if (fi && res->prefixlen < 4)
 			fi = NULL;
+	} else if ((type == RTN_LOCAL) && (orig_oif != 0) &&
+		   (orig_oif != dev_out->ifindex)) {
+		/* For local routes that require a particular output interface
+		 * we do not want to cache the result.  Caching the result
+		 * causes incorrect behaviour when there are multiple source
+		 * addresses on the interface, the end result being that if the
+		 * intended recipient is waiting on that interface for the
+		 * packet he won't receive it because it will be delivered on
+		 * the loopback interface and the IP_PKTINFO ipi_ifindex will
+		 * be set to the loopback interface as well.
+		 */
+		fi = NULL;
 	}
 
 	fnhe = NULL;