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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>
This commit is contained in:
Robert Shearman 2017-03-10 20:43:24 +00:00 committed by David S. Miller
parent b66239b682
commit 5b441ac878
5 changed files with 100 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

11
Documentation/networking/mpls-sysctl.txt
View File

@ -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.

2
include/net/netns/mpls.h
View File

@ -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;
};

1
include/uapi/linux/rtnetlink.h
View File

@ -319,6 +319,7 @@ enum rtattr_type_t {
RTA_EXPIRES,
RTA_PAD,
RTA_UID,
RTA_TTL_PROPAGATE,
__RTA_MAX
};

85
net/mpls/af_mpls.c
View File

@ -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);
/* 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);

7
net/mpls/internal.h
View File

@ -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];