VRF destination unreachable

Greetings,

We found that ICMP destination unreachable isn't sent if VRF
forwarding isn't configured, i.e.
/proc/sys/net/ipv4/conf/<vrf_net_device>/forwarding isn't set. The
relevant code is:

static int ip_error(struct sk_buff *skb)
{
...
        // in_dev is the vrf net_device
        if (!IN_DEV_FORWARD(in_dev)) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);
                        break;

                case ENETUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INNOROUTES);
                        break;
                }
                goto out;
        }
...
out:    kfree_skb(skb);
        return 0;
}

The question: is it intended to be set? The basic forwarding seems to
be working without. We do set it on the slave net devices.

Thank you,

Stephen.

On 2/23/18 10:49 AM, Stephen Suryaputra wrote:

Greetings,

We found that ICMP destination unreachable isn't sent if VRF
forwarding isn't configured, i.e.
/proc/sys/net/ipv4/conf/<vrf_net_device>/forwarding isn't set. The
relevant code is:

static int ip_error(struct sk_buff *skb)
{
...
        // in_dev is the vrf net_device
        if (!IN_DEV_FORWARD(in_dev)) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);
                        break;

                case ENETUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INNOROUTES);
                        break;
                }
                goto out;
        }
...
out:    kfree_skb(skb);
        return 0;
}

The question: is it intended to be set? The basic forwarding seems to
be working without. We do set it on the slave net devices.

Unintended side effect of VRF as a netdev. This should fix it:

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index 5ca7415cd48c..d59d005fb7c5 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c

@@ -944,7 +944,7 @@ static int ip_error(struct sk_buff *skb)
                goto out;

        net = dev_net(rt->dst.dev);
-       if (!IN_DEV_FORWARD(in_dev)) {
+       if (!IN_DEV_FORWARD(in_dev) && !netif_is_l3_master(skb->dev)) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);

Thanks David for confirming that this is unintended.

Given that, I think the fix isn't complete because when forwarding
isn't enabled on the original incoming netdev, the ICMP shouldn't be
generated. This diff fixes that case:

diff --git a/net/ipv4/route.c b/net/ipv4/route.c
index a4f44d8..dc40a94 100644
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c

@@ -937,13 +937,20 @@ static int ip_error(struct sk_buff *skb)
        struct net *net;
        bool send;
        int code;
+       int in_dev_forward;

        /* IP on this device is disabled. */
        if (!in_dev)
                goto out;

        net = dev_net(rt->dst.dev);
-       if (!IN_DEV_FORWARD(in_dev)) {
+       if (netif_is_l3_master(skb->dev)) {
+               in_dev_forward = IN_DEV_FORWARD(
+                       __in_dev_get_rcu(__dev_get_by_index(net,

IPCB(skb)->iif)));
+       } else {
+               in_dev_forward = IN_DEV_FORWARD(in_dev);
+       }
+       if (!in_dev_forward) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);

I can put a formal patch if you like.

Regards,

Stephen.

On Fri, Feb 23, 2018 at 3:58 PM, David Ahern [off-list ref] wrote:

On 2/27/18 9:09 AM, Stephen Suryaputra wrote:

declarations are in reverse xmas tree order. ie., put this new one after
peer.

        /* IP on this device is disabled. */
        if (!in_dev)
                goto out;

        net = dev_net(rt->dst.dev);
-       if (!IN_DEV_FORWARD(in_dev)) {
+       if (netif_is_l3_master(skb->dev)) {
+               in_dev_forward = IN_DEV_FORWARD(
+                       __in_dev_get_rcu(__dev_get_by_index(net,
IPCB(skb)->iif)));
+       } else {
+               in_dev_forward = IN_DEV_FORWARD(in_dev);
+       }

That looks correct.

+       if (!in_dev_forward) {
                switch (rt->dst.error) {
                case EHOSTUNREACH:
                        __IP_INC_STATS(net, IPSTATS_MIB_INADDRERRORS);

I can put a formal patch if you like.

please do.