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Subject[PATCH net-next v3] openvswitch: add TTL decrement action
Date
New action to decrement TTL instead of setting it to a fixed value.
This action will decrement the TTL and, in case of expired TTL, drop it
or execute an action passed via a nested attribute.
The default TTL expired action is to drop the packet.

Supports both IPv4 and IPv6 via the ttl and hop_limit fields, respectively.

Tested with a corresponding change in the userspace:

# ovs-dpctl dump-flows
in_port(2),eth(),eth_type(0x0800), packets:0, bytes:0, used:never, actions:dec_ttl{ttl<=1 action:(drop)},1
in_port(1),eth(),eth_type(0x0800), packets:0, bytes:0, used:never, actions:dec_ttl{ttl<=1 action:(drop)},2
in_port(1),eth(),eth_type(0x0806), packets:0, bytes:0, used:never, actions:2
in_port(2),eth(),eth_type(0x0806), packets:0, bytes:0, used:never, actions:1

# ping -c1 192.168.0.2 -t 42
IP (tos 0x0, ttl 41, id 61647, offset 0, flags [DF], proto ICMP (1), length 84)
192.168.0.1 > 192.168.0.2: ICMP echo request, id 386, seq 1, length 64
# ping -c1 192.168.0.2 -t 120
IP (tos 0x0, ttl 119, id 62070, offset 0, flags [DF], proto ICMP (1), length 84)
192.168.0.1 > 192.168.0.2: ICMP echo request, id 388, seq 1, length 64
# ping -c1 192.168.0.2 -t 1
#

Co-developed-by: Bindiya Kurle <bindiyakurle@gmail.com>
Signed-off-by: Bindiya Kurle <bindiyakurle@gmail.com>
Signed-off-by: Matteo Croce <mcroce@redhat.com>
---
include/uapi/linux/openvswitch.h | 2 +
net/openvswitch/actions.c | 67 ++++++++++++++++++++++++++++++
net/openvswitch/flow_netlink.c | 71 ++++++++++++++++++++++++++++++++
3 files changed, 140 insertions(+)

diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
index ae2bff14e7e1..9d3f040847af 100644
--- a/include/uapi/linux/openvswitch.h
+++ b/include/uapi/linux/openvswitch.h
@@ -958,6 +958,7 @@ enum ovs_action_attr {
OVS_ACTION_ATTR_CLONE, /* Nested OVS_CLONE_ATTR_*. */
OVS_ACTION_ATTR_CHECK_PKT_LEN, /* Nested OVS_CHECK_PKT_LEN_ATTR_*. */
OVS_ACTION_ATTR_ADD_MPLS, /* struct ovs_action_add_mpls. */
+ OVS_ACTION_ATTR_DEC_TTL, /* Nested OVS_DEC_TTL_ATTR_*. */

__OVS_ACTION_ATTR_MAX, /* Nothing past this will be accepted
* from userspace. */
@@ -1050,4 +1051,5 @@ struct ovs_zone_limit {
__u32 count;
};

+#define OVS_DEC_TTL_ATTR_EXEC 0
#endif /* _LINUX_OPENVSWITCH_H */
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 7fbfe2adfffa..1b0afc9bf1ad 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -964,6 +964,26 @@ static int output_userspace(struct datapath *dp, struct sk_buff *skb,
return ovs_dp_upcall(dp, skb, key, &upcall, cutlen);
}

+static int dec_ttl(struct datapath *dp, struct sk_buff *skb,
+ struct sw_flow_key *key,
+ const struct nlattr *attr, bool last)
+{
+ /* The first action is always 'OVS_DEC_TTL_ATTR_ARG'. */
+ struct nlattr *dec_ttl_arg = nla_data(attr);
+ u32 nested = nla_get_u32(dec_ttl_arg);
+ int rem = nla_len(attr);
+
+ if (nested) {
+ struct nlattr *actions = nla_next(dec_ttl_arg, &rem);
+
+ if (actions)
+ return clone_execute(dp, skb, key, 0, actions, rem,
+ last, false);
+ }
+ consume_skb(skb);
+ return 0;
+}
+
/* When 'last' is true, sample() should always consume the 'skb'.
* Otherwise, sample() should keep 'skb' intact regardless what
* actions are executed within sample().
@@ -1180,6 +1200,45 @@ static int execute_check_pkt_len(struct datapath *dp, struct sk_buff *skb,
nla_len(actions), last, clone_flow_key);
}

+static int execute_dec_ttl(struct sk_buff *skb, struct sw_flow_key *key)
+{
+ int err;
+
+ if (skb->protocol == htons(ETH_P_IPV6)) {
+ struct ipv6hdr *nh;
+
+ err = skb_ensure_writable(skb, skb_network_offset(skb) +
+ sizeof(*nh));
+ if (unlikely(err))
+ return err;
+
+ nh = ipv6_hdr(skb);
+
+ if (nh->hop_limit <= 1)
+ return -EHOSTUNREACH;
+
+ key->ip.ttl = --nh->hop_limit;
+ } else {
+ struct iphdr *nh;
+ u8 old_ttl;
+
+ err = skb_ensure_writable(skb, skb_network_offset(skb) +
+ sizeof(*nh));
+ if (unlikely(err))
+ return err;
+
+ nh = ip_hdr(skb);
+ if (nh->ttl <= 1)
+ return -EHOSTUNREACH;
+
+ old_ttl = nh->ttl--;
+ csum_replace2(&nh->check, htons(old_ttl << 8),
+ htons(nh->ttl << 8));
+ key->ip.ttl = nh->ttl;
+ }
+ return 0;
+}
+
/* Execute a list of actions against 'skb'. */
static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
struct sw_flow_key *key,
@@ -1365,6 +1424,14 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,

break;
}
+
+ case OVS_ACTION_ATTR_DEC_TTL:
+ err = execute_dec_ttl(skb, key);
+ if (err == -EHOSTUNREACH) {
+ err = dec_ttl(dp, skb, key, a, true);
+ return err;
+ }
+ break;
}

if (unlikely(err)) {
diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
index 7da4230627f5..0354d5501b70 100644
--- a/net/openvswitch/flow_netlink.c
+++ b/net/openvswitch/flow_netlink.c
@@ -80,6 +80,7 @@ static bool actions_may_change_flow(const struct nlattr *actions)
case OVS_ACTION_ATTR_METER:
case OVS_ACTION_ATTR_CHECK_PKT_LEN:
case OVS_ACTION_ATTR_ADD_MPLS:
+ case OVS_ACTION_ATTR_DEC_TTL:
default:
return true;
}
@@ -2495,6 +2496,40 @@ static int validate_and_copy_sample(struct net *net, const struct nlattr *attr,
return 0;
}

+static int validate_and_copy_dec_ttl(struct net *net,
+ const struct nlattr *attr,
+ const struct sw_flow_key *key,
+ struct sw_flow_actions **sfa,
+ __be16 eth_type, __be16 vlan_tci,
+ u32 mpls_label_count, bool log)
+{
+ u32 nested = true;
+ int start, err;
+
+ if (!nla_len(attr))
+ nested = false;
+
+ start = add_nested_action_start(sfa, OVS_ACTION_ATTR_DEC_TTL, log);
+ if (start < 0)
+ return start;
+
+ err = ovs_nla_add_action(sfa, OVS_DEC_TTL_ATTR_EXEC, &nested,
+ sizeof(nested), log);
+
+ if (err)
+ return err;
+
+ if (nested) {
+ err = __ovs_nla_copy_actions(net, attr, key, sfa, eth_type,
+ vlan_tci, mpls_label_count, log);
+ if (err)
+ return err;
+ }
+
+ add_nested_action_end(*sfa, start);
+ return 0;
+}
+
static int validate_and_copy_clone(struct net *net,
const struct nlattr *attr,
const struct sw_flow_key *key,
@@ -3007,6 +3042,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
[OVS_ACTION_ATTR_CLONE] = (u32)-1,
[OVS_ACTION_ATTR_CHECK_PKT_LEN] = (u32)-1,
[OVS_ACTION_ATTR_ADD_MPLS] = sizeof(struct ovs_action_add_mpls),
+ [OVS_ACTION_ATTR_DEC_TTL] = (u32)-1,
};
const struct ovs_action_push_vlan *vlan;
int type = nla_type(a);
@@ -3267,6 +3303,15 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
break;
}

+ case OVS_ACTION_ATTR_DEC_TTL:
+ err = validate_and_copy_dec_ttl(net, a, key, sfa,
+ eth_type, vlan_tci,
+ mpls_label_count, log);
+ if (err)
+ return err;
+ skip_copy = true;
+ break;
+
default:
OVS_NLERR(log, "Unknown Action type %d", type);
return -EINVAL;
@@ -3438,6 +3483,26 @@ static int check_pkt_len_action_to_attr(const struct nlattr *attr,
return err;
}

+static int dec_ttl_action_to_attr(const struct nlattr *attr,
+ struct sk_buff *skb)
+{
+ int err = 0, rem = nla_len(attr);
+ struct nlattr *start;
+
+ start = nla_nest_start_noflag(skb, OVS_ACTION_ATTR_DEC_TTL);
+
+ if (!start)
+ return -EMSGSIZE;
+
+ err = ovs_nla_put_actions(nla_data(attr), rem, skb);
+ if (err)
+ nla_nest_cancel(skb, start);
+ else
+ nla_nest_end(skb, start);
+
+ return err;
+}
+
static int set_action_to_attr(const struct nlattr *a, struct sk_buff *skb)
{
const struct nlattr *ovs_key = nla_data(a);
@@ -3538,6 +3603,12 @@ int ovs_nla_put_actions(const struct nlattr *attr, int len, struct sk_buff *skb)
return err;
break;

+ case OVS_ACTION_ATTR_DEC_TTL:
+ err = dec_ttl_action_to_attr(a, skb);
+ if (err)
+ return err;
+ break;
+
default:
if (nla_put(skb, type, nla_len(a), nla_data(a)))
return -EMSGSIZE;
--
2.24.1
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