Subject: Re: [PATCH net-next v4 1/2] mpls: multipath route support

From: roopa <[email-masked]>
Date: Thu, 22 Oct 2015 06:33:08 -0700

On 10/22/15, 3:24 AM, Robert Shearman wrote:
> On 19/10/15 02:20, Roopa Prabhu wrote:
>> @@ -159,6 +137,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
>>       struct net *net = dev_net(dev);
>>       struct mpls_shim_hdr *hdr;
>>       struct mpls_route *rt;
>> +    struct mpls_nh *nh;
>>       struct mpls_entry_decoded dec;
>>       struct net_device *out_dev;
>>       struct mpls_dev *mdev;
>> @@ -166,6 +145,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
>>       unsigned int new_header_size;
>>       unsigned int mtu;
>>       int err;
>> +    int nhidx;
>
> nhidx looks to be unused. Remove?

ack,
>
>>
>>       /* Careful this entire function runs inside of an rcu critical section */
>>
>> @@ -196,8 +176,12 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
>>       if (!rt)
>>           goto drop;
>>
>> +    nh = mpls_select_multipath(rt);
>> +    if (!nh)
>> +        goto drop;
>> +
>>       /* Find the output device */
>> -    out_dev = rcu_dereference(rt->rt_dev);
>> +    out_dev = rcu_dereference(nh->nh_dev);
>>       if (!mpls_output_possible(out_dev))
>>           goto drop;
>>
>> @@ -212,7 +196,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
>>       dec.ttl -= 1;
>>
>>       /* Verify the destination can hold the packet */
>> -    new_header_size = mpls_rt_header_size(rt);
>> +    new_header_size = mpls_nh_header_size(nh);
>>       mtu = mpls_dev_mtu(out_dev);
>>       if (mpls_pkt_too_big(skb, mtu - new_header_size))
>>           goto drop;
>> @@ -240,13 +224,14 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
>>           /* Push the new labels */
>>           hdr = mpls_hdr(skb);
>>           bos = dec.bos;
>> -        for (i = rt->rt_labels - 1; i >= 0; i--) {
>> -            hdr[i] = mpls_entry_encode(rt->rt_label[i], dec.ttl, 0, bos);
>> +        for (i = nh->nh_labels - 1; i >= 0; i--) {
>> +            hdr[i] = mpls_entry_encode(nh->nh_label[i],
>> +                           dec.ttl, 0, bos);
>>               bos = false;
>>           }
>>       }
>>
>> -    err = neigh_xmit(rt->rt_via_table, out_dev, rt->rt_via, skb);
>> +    err = neigh_xmit(nh->nh_via_table, out_dev, nh->nh_via, skb);
>>       if (err)
>>           net_dbg_ratelimited("%s: packet transmission failed: %d\n",
>>                       __func__, err);
>
>>       return dev;
>>   }
>>
>> +static int mpls_nh_assign_dev(struct net *net, struct mpls_nh *nh, int oif)
>> +{
>> +    struct net_device *dev = NULL;
>> +    int err = -ENODEV;
>> +
>> +    dev = find_outdev(net, nh, oif);
>> +    if (IS_ERR(dev)) {
>> +        err = PTR_ERR(dev);
>> +        dev = NULL;
>> +        goto errout;
>> +    }
>> +
>> +    /* Ensure this is a supported device */
>> +    err = -EINVAL;
>> +    if (!mpls_dev_get(dev))
>> +        goto errout;
>> +
>> +    /* For now just support ethernet devices */
>> +    if ((dev->type != ARPHRD_ETHER) && (dev->type != ARPHRD_LOOPBACK))
>> +        goto errout;
>> +
>> +    RCU_INIT_POINTER(nh->nh_dev, dev);
>> +    dev_put(dev);
>
> If it's safe to not keep a reference to dev (i.e. because the device cannot go away while a netlink message is being processed), then why not just change find_outdev to use __dev_get_by_index?
yes, rtnl is held here. dev_get_by_index was used by the original code. So i did not feel the need to change that.
I can see the need to get away with the dev_hold instead of doing a dev_hold with dev_get_by_index, rcu assign and put because of rtnl. But, it seems cleaner to use it the way it is today, given the other cases where the dev is already held during lookup when oif is not specified.

> If the dev can go away during this, then we could end up adding an mpls route that points to a freed interface, because until we've added the route to the label table mpls_ifdown won't find it.
dev should not go away because we have rtnl held at this point. no ?
If there is a problem i can think about moving the dev_put's for nexthop devs after mpls_route_update
>
>> +
>> +    return 0;
>> +
>> +errout:
>> +    if (dev)
>> +        dev_put(dev);
>> +    return err;
>> +}
>> +
>
>>   }
>>   EXPORT_SYMBOL_GPL(nla_get_labels);
>>
>> +int nla_get_via(const struct nlattr *nla, u8 *via_alen,
>> +        u8 *via_table, u8 via_addr[])
>> +{
>> +    struct rtvia *via = nla_data(nla);
>> +    int err = -EINVAL;
>> +    u8 alen;
>
> This should be an int to avoid nexthop address lengths > 255 wrapping and possibly accepted instead of rejected.
ack
>
>> +
>> +    if (nla_len(nla) < offsetof(struct rtvia, rtvia_addr))
>> +        goto errout;
>> +    alen = nla_len(nla) -
>> +            offsetof(struct rtvia, rtvia_addr);
>> +    if (alen > MAX_VIA_ALEN)
>> +        goto errout;
>> +
>> +    /* Validate the address family */
>> +    switch(via->rtvia_family) {
>> +    case AF_PACKET:
>> +        *via_table = NEIGH_LINK_TABLE;
>> +        break;
>> +    case AF_INET:
>> +        *via_table = NEIGH_ARP_TABLE;
>> +        if (alen != 4)
>> +            goto errout;
>> +        break;
>> +    case AF_INET6:
>> +        *via_table = NEIGH_ND_TABLE;
>> +        if (alen != 16)
>> +            goto errout;
>> +        break;
>> +    default:
>> +        /* Unsupported address family */
>> +        goto errout;
>> +    }
>> +
>> +    memcpy(via_addr, via->rtvia_addr, alen);
>> +    *via_alen = alen;
>> +    err = 0;
>> +
>> +errout:
>> +    return err;
>> +}
>> +
>>   static int rtm_to_route_config(struct sk_buff *skb,  struct nlmsghdr *nlh,
>>                      struct mpls_route_config *cfg)
>>   {
>
>
> Otherwise, looks good.
>
Thanks for the review.