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openvswitch: add TTL decrement action
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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>
Acked-by: Pravin B Shelar <pshelar@ovn.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Matteo Croce authored and David S. Miller committed Feb 17, 2020
1 parent 7458bd5 commit 744676e
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7 changes: 7 additions & 0 deletions include/uapi/linux/openvswitch.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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. */
Expand Down Expand Up @@ -1050,4 +1051,10 @@ struct ovs_zone_limit {
__u32 count;
};

enum ovs_dec_ttl_attr {
OVS_DEC_TTL_ATTR_UNSPEC,
OVS_DEC_TTL_ATTR_ACTION, /* Nested struct nlattr */
__OVS_DEC_TTL_ATTR_MAX
};

#endif /* _LINUX_OPENVSWITCH_H */
67 changes: 67 additions & 0 deletions net/openvswitch/actions.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -964,6 +964,25 @@ static int output_userspace(struct datapath *dp, struct sk_buff *skb,
return ovs_dp_upcall(dp, skb, key, &upcall, cutlen);
}

static int dec_ttl_exception_handler(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);
int rem = nla_len(attr);

if (nla_len(dec_ttl_arg)) {
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().
Expand Down Expand Up @@ -1180,6 +1199,45 @@ 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,
Expand Down Expand Up @@ -1365,6 +1423,15 @@ 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_exception_handler(dp, skb, key,
a, true);
return err;
}
break;
}

if (unlikely(err)) {
Expand Down
70 changes: 70 additions & 0 deletions net/openvswitch/flow_netlink.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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;
}
Expand Down Expand Up @@ -2495,6 +2496,39 @@ 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)
{
int start, err;
u32 nested = true;

if (!nla_len(attr))
return ovs_nla_add_action(sfa, OVS_ACTION_ATTR_DEC_TTL,
NULL, 0, log);

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_ACTION, &nested,
sizeof(nested), log);

if (err)
return err;

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,
Expand Down Expand Up @@ -3007,6 +3041,7 @@ 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);
Expand Down Expand Up @@ -3267,6 +3302,15 @@ 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;
Expand Down Expand Up @@ -3438,6 +3482,26 @@ 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);
Expand Down Expand Up @@ -3538,6 +3602,12 @@ 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;
Expand Down

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