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Date: Thu, 06 Jul 2023 08:54:16 -0400
From: Aaron Conole <aconole@...hat.com>
To: Eric Garver <eric@...ver.life>
Cc: netdev@...r.kernel.org, dev@...nvswitch.org, Ilya Maximets
<i.maximets@....org>
Subject: Re: [ovs-dev] [PATCH net-next 2/2] net: openvswitch: add drop action
Eric Garver <eric@...ver.life> writes:
> This adds an explicit drop action. This is used by OVS to drop packets
> for which it cannot determine what to do. An explicit action in the
> kernel allows passing the reason _why_ the packet is being dropped. We
> can then use perf tracing to match on the drop reason.
>
> e.g. trace all OVS dropped skbs
>
> # perf trace -e skb:kfree_skb --filter="reason >= 0x30000"
> [..]
> 106.023 ping/2465 skb:kfree_skb(skbaddr: 0xffffa0e8765f2000, \
> location:0xffffffffc0d9b462, protocol: 2048, reason: 196610)
>
> reason: 196610 --> 0x30002 (OVS_XLATE_RECURSION_TOO_DEEP)
>
> Signed-off-by: Eric Garver <eric@...ver.life>
> ---
> include/uapi/linux/openvswitch.h | 2 ++
> net/openvswitch/actions.c | 13 +++++++++++++
> net/openvswitch/flow_netlink.c | 12 +++++++++++-
> .../testing/selftests/net/openvswitch/ovs-dpctl.py | 3 +++
> 4 files changed, 29 insertions(+), 1 deletion(-)
>
> diff --git a/include/uapi/linux/openvswitch.h b/include/uapi/linux/openvswitch.h
> index e94870e77ee9..a967dbca3574 100644
> --- a/include/uapi/linux/openvswitch.h
> +++ b/include/uapi/linux/openvswitch.h
> @@ -965,6 +965,7 @@ struct check_pkt_len_arg {
> * start of the packet or at the start of the l3 header depending on the value
> * of l3 tunnel flag in the tun_flags field of OVS_ACTION_ATTR_ADD_MPLS
> * argument.
> + * @OVS_ACTION_ATTR_DROP: Explicit drop action.
> *
> * Only a single header can be set with a single %OVS_ACTION_ATTR_SET. Not all
> * fields within a header are modifiable, e.g. the IPv4 protocol and fragment
> @@ -1002,6 +1003,7 @@ enum ovs_action_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_DROP, /* u32 xlate_error. */
>
> __OVS_ACTION_ATTR_MAX, /* Nothing past this will be accepted
> * from userspace. */
> diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
> index cab1e02b63e0..4ad9a45dc042 100644
> --- a/net/openvswitch/actions.c
> +++ b/net/openvswitch/actions.c
> @@ -32,6 +32,7 @@
> #include "vport.h"
> #include "flow_netlink.h"
> #include "openvswitch_trace.h"
> +#include "drop.h"
>
> struct deferred_action {
> struct sk_buff *skb;
> @@ -1477,6 +1478,18 @@ static int do_execute_actions(struct datapath *dp, struct sk_buff *skb,
> return dec_ttl_exception_handler(dp, skb,
> key, a);
> break;
> +
> + case OVS_ACTION_ATTR_DROP:
> + u32 reason = nla_get_u32(a);
> +
> + reason |= SKB_DROP_REASON_SUBSYS_OPENVSWITCH <<
> + SKB_DROP_REASON_SUBSYS_SHIFT;
> +
> + if (reason == OVS_XLATE_OK)
> + break;
> +
> + kfree_skb_reason(skb, reason);
> + return 0;
> }
>
> if (unlikely(err)) {
> diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
> index 41116361433d..23d39eae9a0d 100644
> --- a/net/openvswitch/flow_netlink.c
> +++ b/net/openvswitch/flow_netlink.c
> @@ -39,6 +39,7 @@
> #include <net/erspan.h>
>
> #include "flow_netlink.h"
> +#include "drop.h"
>
> struct ovs_len_tbl {
> int len;
> @@ -61,6 +62,7 @@ static bool actions_may_change_flow(const struct nlattr *actions)
> case OVS_ACTION_ATTR_RECIRC:
> case OVS_ACTION_ATTR_TRUNC:
> case OVS_ACTION_ATTR_USERSPACE:
> + case OVS_ACTION_ATTR_DROP:
> break;
>
> case OVS_ACTION_ATTR_CT:
> @@ -2394,7 +2396,7 @@ static void ovs_nla_free_nested_actions(const struct nlattr *actions, int len)
> /* Whenever new actions are added, the need to update this
> * function should be considered.
> */
> - BUILD_BUG_ON(OVS_ACTION_ATTR_MAX != 23);
> + BUILD_BUG_ON(OVS_ACTION_ATTR_MAX != 24);
>
> if (!actions)
> return;
> @@ -3182,6 +3184,7 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> [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,
> + [OVS_ACTION_ATTR_DROP] = sizeof(u32),
> };
> const struct ovs_action_push_vlan *vlan;
> int type = nla_type(a);
> @@ -3453,6 +3456,13 @@ static int __ovs_nla_copy_actions(struct net *net, const struct nlattr *attr,
> skip_copy = true;
> break;
>
> + case OVS_ACTION_ATTR_DROP:
> + if (nla_get_u32(a) >=
> + u32_get_bits(OVS_XLATE_MAX,
> + ~SKB_DROP_REASON_SUBSYS_MASK))
> + return -EINVAL;
> + break;
> +
If there's a case where the userspace sends a drop reason that isn't
known to the kernel, we will reject the flow, and the only "close" drop
will be OVS_XLATE_OK, which would be wrong. Is there a reason to do
this? For example, userspace might get new support for some kind of
flows and during that time might have a new xlate drop reason. Maybe we
can have a reason code that OVS knows will exist, so that if this fails,
it can at least fall back to that?
> default:
> OVS_NLERR(log, "Unknown Action type %d", type);
> return -EINVAL;
> diff --git a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
> index 1c8b36bc15d4..526ebad7d514 100644
> --- a/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
> +++ b/tools/testing/selftests/net/openvswitch/ovs-dpctl.py
> @@ -115,6 +115,7 @@ class ovsactions(nla):
> ("OVS_ACTION_ATTR_CHECK_PKT_LEN", "none"),
> ("OVS_ACTION_ATTR_ADD_MPLS", "none"),
> ("OVS_ACTION_ATTR_DEC_TTL", "none"),
> + ("OVS_ACTION_ATTR_DROP", "uint32"),
> )
>
> class ctact(nla):
> @@ -261,6 +262,8 @@ class ovsactions(nla):
> print_str += "recirc(0x%x)" % int(self.get_attr(field[0]))
> elif field[0] == "OVS_ACTION_ATTR_TRUNC":
> print_str += "trunc(%d)" % int(self.get_attr(field[0]))
> + elif field[0] == "OVS_ACTION_ATTR_DROP":
> + print_str += "drop"
Can we also include the reason here?
> elif field[1] == "flag":
> if field[0] == "OVS_ACTION_ATTR_CT_CLEAR":
> print_str += "ct_clear"
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