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SubjectRe: [PATCH net-next v3] openvswitch: add TTL decrement action
On Wed, Jan 15, 2020 at 8:40 AM Matteo Croce <mcroce@redhat.com> wrote:
>
> 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
> #
>
Thanks for the patch.

> 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

I am not sure if we need this, But if you want the nested attribute
then lets define enum with this single attribute and have actions as
part of its data. This would be optional argument, so userspace can
skip it, and in that case datapath can drop the packet.

> #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)
Can you give it better name, for example: dec_ttl_exception_handler().

> +{
> + /* 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;
> +
As mentioned above if there are no nested action, I do not see need to
add this flag. In Fast path, action can check size of data of
attribute OVS_ACTION_ATTR_DEC_TTL. In case it is zero we can drop the
packet.

> + 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);
> +
Same here, we can check the size of data and depending on that add
nested attribute OVS_DEC_TTL_ATTR_EXEC.

> + 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
Let me know what kind of testing you have done for nested action case.

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