mpls: allow TTL propagation to IP packets to be configured

Provide the ability to control on a per-route basis whether the TTL
value from an MPLS packet is propagated to an IPv4/IPv6 packet when
the last label is popped as per the theoretical model in RFC 3443
through a new route attribute, RTA_TTL_PROPAGATE which can be 0 to
mean disable propagation and 1 to mean enable propagation.

In order to provide the ability to change the behaviour for packets
arriving with IPv4/IPv6 Explicit Null labels and to provide an easy
way for a user to change the behaviour for all existing routes without
having to reprogram them, a global knob is provided. This is done
through the addition of a new per-namespace sysctl,
"net.mpls.ip_ttl_propagate", which defaults to enabled. If the
per-route attribute is set (either enabled or disabled) then it
overrides the global configuration.

Signed-off-by: Robert Shearman <rshearma@brocade.com>
Acked-by: David Ahern <dsa@cumulusnetworks.com>
Tested-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/Documentation/networking/mpls-sysctl.txt b/Documentation/networking/mpls-sysctl.txt
index 15d8d16934fd13727bb35e9c5078484127bbfa30..9badd1d6685f553a6d6726b272b63c8ba1e3b71b 100644 (file)
--- a/Documentation/networking/mpls-sysctl.txt
+++ b/Documentation/networking/mpls-sysctl.txt
@@ -19,6 +19,17 @@ platform_labels - INTEGER
        Possible values: 0 - 1048575
        Default: 0
 
+ip_ttl_propagate - BOOL
+       Control whether TTL is propagated from the IPv4/IPv6 header to
+       the MPLS header on imposing labels and propagated from the
+       MPLS header to the IPv4/IPv6 header on popping the last label.
+
+       If disabled, the MPLS transport network will appear as a
+       single hop to transit traffic.
+
+       0 - disabled / RFC 3443 [Short] Pipe Model
+       1 - enabled / RFC 3443 Uniform Model (default)
+
 conf/<interface>/input - BOOL
        Control whether packets can be input on this interface.
 

diff --git a/include/net/netns/mpls.h b/include/net/netns/mpls.h
index d29203651c01700d9406157ef8dd016ea55a4cbb..08652eedabb2820b44306e5eef0327b853f37b28 100644 (file)
--- a/include/net/netns/mpls.h
+++ b/include/net/netns/mpls.h
@@ -9,8 +9,10 @@ struct mpls_route;
 struct ctl_table_header;
 
 struct netns_mpls {
+       int ip_ttl_propagate;
        size_t platform_labels;
        struct mpls_route __rcu * __rcu *platform_label;
+
        struct ctl_table_header *ctl;
 };
 

diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
index 75fcf5eff093a7164f5b4071d425b9a9ec322cc7..3dd72aee4d32aa855adb69f96412ebad8e786904 100644 (file)
--- a/include/uapi/linux/rtnetlink.h
+++ b/include/uapi/linux/rtnetlink.h
@@ -319,6 +319,7 @@ enum rtattr_type_t {
        RTA_EXPIRES,
        RTA_PAD,
        RTA_UID,
+       RTA_TTL_PROPAGATE,
        __RTA_MAX
 };
 

diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
index 3818686182b210be11025ff69d82f58e4e08e401..0e1046f21af810dc9fc5f2d7d59ce0b8b186a547 100644 (file)
--- a/net/mpls/af_mpls.c
+++ b/net/mpls/af_mpls.c
@@ -32,6 +32,7 @@
 #define MPLS_NEIGH_TABLE_UNSPEC (NEIGH_LINK_TABLE + 1)
 
 static int zero = 0;
+static int one = 1;
 static int label_limit = (1 << 20) - 1;
 
 static void rtmsg_lfib(int event, u32 label, struct mpls_route *rt,
@@ -220,8 +221,8 @@ out:
        return &rt->rt_nh[nh_index];
 }
 
-static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
-                       struct mpls_entry_decoded dec)
+static bool mpls_egress(struct net *net, struct mpls_route *rt,
+                       struct sk_buff *skb, struct mpls_entry_decoded dec)
 {
        enum mpls_payload_type payload_type;
        bool success = false;
@@ -246,22 +247,46 @@ static bool mpls_egress(struct mpls_route *rt, struct sk_buff *skb,
        switch (payload_type) {
        case MPT_IPV4: {
                struct iphdr *hdr4 = ip_hdr(skb);
+               u8 new_ttl;
                skb->protocol = htons(ETH_P_IP);
+
+               /* If propagating TTL, take the decremented TTL from
+                * the incoming MPLS header, otherwise decrement the
+                * TTL, but only if not 0 to avoid underflow.
+                */
+               if (rt->rt_ttl_propagate == MPLS_TTL_PROP_ENABLED ||
+                   (rt->rt_ttl_propagate == MPLS_TTL_PROP_DEFAULT &&
+                    net->mpls.ip_ttl_propagate))
+                       new_ttl = dec.ttl;
+               else
+                       new_ttl = hdr4->ttl ? hdr4->ttl - 1 : 0;
+
                csum_replace2(&hdr4->check,
                              htons(hdr4->ttl << 8),
-                             htons(dec.ttl << 8));
-               hdr4->ttl = dec.ttl;
+                             htons(new_ttl << 8));
+               hdr4->ttl = new_ttl;
                success = true;
                break;
        }
        case MPT_IPV6: {
                struct ipv6hdr *hdr6 = ipv6_hdr(skb);
                skb->protocol = htons(ETH_P_IPV6);
-               hdr6->hop_limit = dec.ttl;
+
+               /* If propagating TTL, take the decremented TTL from
+                * the incoming MPLS header, otherwise decrement the
+                * hop limit, but only if not 0 to avoid underflow.
+                */
+               if (rt->rt_ttl_propagate == MPLS_TTL_PROP_ENABLED ||
+                   (rt->rt_ttl_propagate == MPLS_TTL_PROP_DEFAULT &&
+                    net->mpls.ip_ttl_propagate))
+                       hdr6->hop_limit = dec.ttl;
+               else if (hdr6->hop_limit)
+                       hdr6->hop_limit = hdr6->hop_limit - 1;
                success = true;
                break;
        }
        case MPT_UNSPEC:
+               /* Should have decided which protocol it is by now */
                break;
        }
 
@@ -361,7 +386,7 @@ static int mpls_forward(struct sk_buff *skb, struct net_device *dev,
 
        if (unlikely(!new_header_size && dec.bos)) {
                /* Penultimate hop popping */
-               if (!mpls_egress(rt, skb, dec))
+               if (!mpls_egress(dev_net(out_dev), rt, skb, dec))
                        goto err;
        } else {
                bool bos;
@@ -412,6 +437,7 @@ static struct packet_type mpls_packet_type __read_mostly = {
 static const struct nla_policy rtm_mpls_policy[RTA_MAX+1] = {
        [RTA_DST]               = { .type = NLA_U32 },
        [RTA_OIF]               = { .type = NLA_U32 },
+       [RTA_TTL_PROPAGATE]     = { .type = NLA_U8 },
 };
 
 struct mpls_route_config {
@@ -421,6 +447,7 @@ struct mpls_route_config {
        u8                      rc_via_alen;
        u8                      rc_via[MAX_VIA_ALEN];
        u32                     rc_label;
+       u8                      rc_ttl_propagate;
        u8                      rc_output_labels;
        u32                     rc_output_label[MAX_NEW_LABELS];
        u32                     rc_nlflags;
@@ -856,6 +883,7 @@ static int mpls_route_add(struct mpls_route_config *cfg)
 
        rt->rt_protocol = cfg->rc_protocol;
        rt->rt_payload_type = cfg->rc_payload_type;
+       rt->rt_ttl_propagate = cfg->rc_ttl_propagate;
 
        if (cfg->rc_mp)
                err = mpls_nh_build_multi(cfg, rt);
@@ -1576,6 +1604,7 @@ static int rtm_to_route_config(struct sk_buff *skb,  struct nlmsghdr *nlh,
        cfg->rc_label           = LABEL_NOT_SPECIFIED;
        cfg->rc_protocol        = rtm->rtm_protocol;
        cfg->rc_via_table       = MPLS_NEIGH_TABLE_UNSPEC;
+       cfg->rc_ttl_propagate   = MPLS_TTL_PROP_DEFAULT;
        cfg->rc_nlflags         = nlh->nlmsg_flags;
        cfg->rc_nlinfo.portid   = NETLINK_CB(skb).portid;
        cfg->rc_nlinfo.nlh      = nlh;
@@ -1622,6 +1651,17 @@ static int rtm_to_route_config(struct sk_buff *skb,  struct nlmsghdr *nlh,
                        cfg->rc_mp_len = nla_len(nla);
                        break;
                }
+               case RTA_TTL_PROPAGATE:
+               {
+                       u8 ttl_propagate = nla_get_u8(nla);
+
+                       if (ttl_propagate > 1)
+                               goto errout;
+                       cfg->rc_ttl_propagate = ttl_propagate ?
+                               MPLS_TTL_PROP_ENABLED :
+                               MPLS_TTL_PROP_DISABLED;
+                       break;
+               }
                default:
                        /* Unsupported attribute */
                        goto errout;
@@ -1682,6 +1722,15 @@ static int mpls_dump_route(struct sk_buff *skb, u32 portid, u32 seq, int event,
 
        if (nla_put_labels(skb, RTA_DST, 1, &label))
                goto nla_put_failure;
+
+       if (rt->rt_ttl_propagate != MPLS_TTL_PROP_DEFAULT) {
+               bool ttl_propagate =
+                       rt->rt_ttl_propagate == MPLS_TTL_PROP_ENABLED;
+
+               if (nla_put_u8(skb, RTA_TTL_PROPAGATE,
+                              ttl_propagate))
+                       goto nla_put_failure;
+       }
        if (rt->rt_nhn == 1) {
                const struct mpls_nh *nh = rt->rt_nh;
 
@@ -1792,7 +1841,8 @@ static inline size_t lfib_nlmsg_size(struct mpls_route *rt)
 {
        size_t payload =
                NLMSG_ALIGN(sizeof(struct rtmsg))
-               + nla_total_size(4);                    /* RTA_DST */
+               + nla_total_size(4)                     /* RTA_DST */
+               + nla_total_size(1);                    /* RTA_TTL_PROPAGATE */
 
        if (rt->rt_nhn == 1) {
                struct mpls_nh *nh = rt->rt_nh;
@@ -1876,6 +1926,7 @@ static int resize_platform_label_table(struct net *net, size_t limit)
                RCU_INIT_POINTER(rt0->rt_nh->nh_dev, lo);
                rt0->rt_protocol = RTPROT_KERNEL;
                rt0->rt_payload_type = MPT_IPV4;
+               rt0->rt_ttl_propagate = MPLS_TTL_PROP_DEFAULT;
                rt0->rt_nh->nh_via_table = NEIGH_LINK_TABLE;
                rt0->rt_nh->nh_via_alen = lo->addr_len;
                memcpy(__mpls_nh_via(rt0, rt0->rt_nh), lo->dev_addr,
@@ -1889,6 +1940,7 @@ static int resize_platform_label_table(struct net *net, size_t limit)
                RCU_INIT_POINTER(rt2->rt_nh->nh_dev, lo);
                rt2->rt_protocol = RTPROT_KERNEL;
                rt2->rt_payload_type = MPT_IPV6;
+               rt0->rt_ttl_propagate = MPLS_TTL_PROP_DEFAULT;
                rt2->rt_nh->nh_via_table = NEIGH_LINK_TABLE;
                rt2->rt_nh->nh_via_alen = lo->addr_len;
                memcpy(__mpls_nh_via(rt2, rt2->rt_nh), lo->dev_addr,
@@ -1970,6 +2022,9 @@ static int mpls_platform_labels(struct ctl_table *table, int write,
        return ret;
 }
 
+#define MPLS_NS_SYSCTL_OFFSET(field)           \
+       (&((struct net *)0)->field)
+
 static const struct ctl_table mpls_table[] = {
        {
                .procname       = "platform_labels",
@@ -1978,21 +2033,37 @@ static const struct ctl_table mpls_table[] = {
                .mode           = 0644,
                .proc_handler   = mpls_platform_labels,
        },
+       {
+               .procname       = "ip_ttl_propagate",
+               .data           = MPLS_NS_SYSCTL_OFFSET(mpls.ip_ttl_propagate),
+               .maxlen         = sizeof(int),
+               .mode           = 0644,
+               .proc_handler   = proc_dointvec_minmax,
+               .extra1         = &zero,
+               .extra2         = &one,
+       },
        { }
 };
 
 static int mpls_net_init(struct net *net)
 {
        struct ctl_table *table;
+       int i;
 
        net->mpls.platform_labels = 0;
        net->mpls.platform_label = NULL;
+       net->mpls.ip_ttl_propagate = 1;
 
        table = kmemdup(mpls_table, sizeof(mpls_table), GFP_KERNEL);
        if (table == NULL)
                return -ENOMEM;
 
-       table[0].data = net;
+       /* Table data contains only offsets relative to the base of
+        * the mdev at this point, so make them absolute.
+        */
+       for (i = 0; i < ARRAY_SIZE(mpls_table) - 1; i++)
+               table[i].data = (char *)net + (uintptr_t)table[i].data;
+
        net->mpls.ctl = register_net_sysctl(net, "net/mpls", table);
        if (net->mpls.ctl == NULL) {
                kfree(table);

diff --git a/net/mpls/internal.h b/net/mpls/internal.h
index 76360d8b95798e148c5d6a48ce3375eeadcad5a5..62928d8fabd1b94eaf67aa46043a6ce40b525113 100644 (file)
--- a/net/mpls/internal.h
+++ b/net/mpls/internal.h
@@ -90,6 +90,12 @@ struct mpls_nh { /* next hop label forwarding entry */
        u8                      nh_via_table;
 };
 
+enum mpls_ttl_propagation {
+       MPLS_TTL_PROP_DEFAULT,
+       MPLS_TTL_PROP_ENABLED,
+       MPLS_TTL_PROP_DISABLED,
+};
+
 /* The route, nexthops and vias are stored together in the same memory
  * block:
  *
@@ -116,6 +122,7 @@ struct mpls_route { /* next hop label forwarding entry */
        u8                      rt_protocol;
        u8                      rt_payload_type;
        u8                      rt_max_alen;
+       u8                      rt_ttl_propagate;
        unsigned int            rt_nhn;
        unsigned int            rt_nhn_alive;
        struct mpls_nh          rt_nh[0];