[PATCH net-next v3 0/2] net/bridge: Add skb drop reasons to the most common drop points

[PATCH net-next v3 0/2] net/bridge: Add skb drop reasons to the most common drop points

[Radu Rendec]

The bridge input code may drop frames for various reasons and at various
points in the ingress handling logic. Currently kfree_skb() is used
everywhere, and therefore no drop reason is specified. Add drop reasons
to the most common drop points.

The purpose of this series is to address the most common drop points on
the bridge ingress path. It does not exhaustively add drop reasons to
the entire bridge code. The intention here is to incrementally add drop
reasons to the rest of the bridge code in follow up patches.

Most of the skb drop points that are addressed in this series can be
easily tested by sending crafted packets. The diagram below shows a
simple test configuration, and some examples using `packit`(*) are
also included. The bridge is set up with STP disabled.
(*) https://github.com/resurrecting-open-source-projects/packit

The following changes were *not* tested:
* SKB_DROP_REASON_NOMEM in br_flood(). It's not easy to trigger an OOM
  condition for testing purposes, while everything else works correctly.
* All drop reasons in br_multicast_flood(). I could not find an easy way
  to make a crafted packet get there.
* SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE in br_handle_frame_finish()
  when the port state is BR_STATE_DISABLED, because in that case the
  frame is already dropped in the switch/case block at the end of
  br_handle_frame().

    +-------+
    |  br0  |
    +---+---+
        |
    +---+---+  veth pair  +-------+
    | veth0 +-------------+ xeth0 |
    +-------+             +-------+

SKB_DROP_REASON_MAC_INVALID_SOURCE - br_handle_frame()
packit -t UDP -s 192.168.0.1 -d 192.168.0.2 -S 8000 -D 8000 \
  -e 01:22:33:44:55:66 -E aa:bb:cc:dd:ee:ff -c 1 \
  -p '0x de ad be ef' -i xeth0

SKB_DROP_REASON_MAC_IEEE_MAC_CONTROL - br_handle_frame()
packit -t UDP -s 192.168.0.1 -d 192.168.0.2 -S 8000 -D 8000 \
  -e 02:22:33:44:55:66 -E 01:80:c2:00:00:01 -c 1 \
  -p '0x de ad be ef' -i xeth0

SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE - br_handle_frame()
bridge link set dev veth0 state 0 # disabled
packit -t UDP -s 192.168.0.1 -d 192.168.0.2 -S 8000 -D 8000 \
  -e 02:22:33:44:55:66 -E aa:bb:cc:dd:ee:ff -c 1 \
  -p '0x de ad be ef' -i xeth0

SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE - br_handle_frame_finish()
bridge link set dev veth0 state 2 # learning
packit -t UDP -s 192.168.0.1 -d 192.168.0.2 -S 8000 -D 8000 \
  -e 02:22:33:44:55:66 -E aa:bb:cc:dd:ee:ff -c 1 \
  -p '0x de ad be ef' -i xeth0

SKB_DROP_REASON_NO_TX_TARGET - br_flood()
packit -t UDP -s 192.168.0.1 -d 192.168.0.2 -S 8000 -D 8000 \
  -e 02:22:33:44:55:66 -E aa:bb:cc:dd:ee:ff -c 1 \
  -p '0x de ad be ef' -i xeth0

Changes since v2:
- Minor update to the description of SKB_DROP_REASON_NO_TX_TARGET.
- Do not trigger a warning in br_flood() and br_multicast_flood() if
  maybe_deliver() returns a different error than -ENOMEM.
- Keep the error path consolidated in br_handle_frame_finish() and
  br_handle_frame(), and use a `reason` variable.

Changes since v1:
- Add patch #1, which makes it possible to reuse the existing
  SKB_DROP_REASON_VXLAN_NO_REMOTE drop reason from vxlan in the bridge
  module, where a similar drop case exists.
- Don't add SKB_DROP_REASON_BRIDGE_NO_EGRESS_PORT. Instead, use either
  SKB_DROP_REASON_NO_TX_TARGET or SKB_DROP_REASON_NOMEM, depending on
  the case.
- For better clarity, rename SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD to
  SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE.

Radu Rendec (2):
  net: vxlan: rename SKB_DROP_REASON_VXLAN_NO_REMOTE
  net: bridge: add skb drop reasons to the most common drop points

 drivers/net/vxlan/vxlan_core.c |  4 ++--
 drivers/net/vxlan/vxlan_mdb.c  |  2 +-
 include/net/dropreason-core.h  | 18 +++++++++++++++---
 net/bridge/br_forward.c        | 16 ++++++++++++----
 net/bridge/br_input.c          | 20 +++++++++++++++-----
 5 files changed, 45 insertions(+), 15 deletions(-)

-- 
2.47.1

[PATCH net-next v3 1/2] net: vxlan: rename SKB_DROP_REASON_VXLAN_NO_REMOTE

[Radu Rendec]

The SKB_DROP_REASON_VXLAN_NO_REMOTE skb drop reason was introduced in
the specific context of vxlan. As it turns out, there are similar cases
when a packet needs to be dropped in other parts of the network stack,
such as the bridge module.

Rename SKB_DROP_REASON_VXLAN_NO_REMOTE and give it a more generic name,
so that it can be used in other parts of the network stack. This is not
a functional change, and the numeric value of the drop reason even
remains unchanged.

Signed-off-by: Radu Rendec <rrendec@redhat.com>
---
 drivers/net/vxlan/vxlan_core.c | 4 ++--
 drivers/net/vxlan/vxlan_mdb.c  | 2 +-
 include/net/dropreason-core.h  | 6 +++---
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/net/vxlan/vxlan_core.c b/drivers/net/vxlan/vxlan_core.c
index 0c356e0a61ef0..05c10acb2a57e 100644
--- a/drivers/net/vxlan/vxlan_core.c
+++ b/drivers/net/vxlan/vxlan_core.c
@@ -2798,7 +2798,7 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
 			dev_dstats_tx_dropped(dev);
 			vxlan_vnifilter_count(vxlan, vni, NULL,
 					      VXLAN_VNI_STATS_TX_DROPS, 0);
-			kfree_skb_reason(skb, SKB_DROP_REASON_VXLAN_NO_REMOTE);
+			kfree_skb_reason(skb, SKB_DROP_REASON_NO_TX_TARGET);
 			return NETDEV_TX_OK;
 		}
 	}
@@ -2821,7 +2821,7 @@ static netdev_tx_t vxlan_xmit(struct sk_buff *skb, struct net_device *dev)
 		if (fdst)
 			vxlan_xmit_one(skb, dev, vni, fdst, did_rsc);
 		else
-			kfree_skb_reason(skb, SKB_DROP_REASON_VXLAN_NO_REMOTE);
+			kfree_skb_reason(skb, SKB_DROP_REASON_NO_TX_TARGET);
 	}
 
 	return NETDEV_TX_OK;
diff --git a/drivers/net/vxlan/vxlan_mdb.c b/drivers/net/vxlan/vxlan_mdb.c
index 8735891ee1286..816ab1aa05262 100644
--- a/drivers/net/vxlan/vxlan_mdb.c
+++ b/drivers/net/vxlan/vxlan_mdb.c
@@ -1712,7 +1712,7 @@ netdev_tx_t vxlan_mdb_xmit(struct vxlan_dev *vxlan,
 		vxlan_xmit_one(skb, vxlan->dev, src_vni,
 			       rcu_dereference(fremote->rd), false);
 	else
-		kfree_skb_reason(skb, SKB_DROP_REASON_VXLAN_NO_REMOTE);
+		kfree_skb_reason(skb, SKB_DROP_REASON_NO_TX_TARGET);
 
 	return NETDEV_TX_OK;
 }
diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index ead4170a1d0a9..6e32106d72294 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -106,7 +106,7 @@
 	FN(VXLAN_VNI_NOT_FOUND)		\
 	FN(MAC_INVALID_SOURCE)		\
 	FN(VXLAN_ENTRY_EXISTS)		\
-	FN(VXLAN_NO_REMOTE)		\
+	FN(NO_TX_TARGET)		\
 	FN(IP_TUNNEL_ECN)		\
 	FN(TUNNEL_TXINFO)		\
 	FN(LOCAL_MAC)			\
@@ -497,8 +497,8 @@ enum skb_drop_reason {
 	 * entry or an entry pointing to a nexthop.
 	 */
 	SKB_DROP_REASON_VXLAN_ENTRY_EXISTS,
-	/** @SKB_DROP_REASON_VXLAN_NO_REMOTE: no remote found for xmit */
-	SKB_DROP_REASON_VXLAN_NO_REMOTE,
+	/** @SKB_DROP_REASON_NO_TX_TARGET: no target found for xmit */
+	SKB_DROP_REASON_NO_TX_TARGET,
 	/**
 	 * @SKB_DROP_REASON_IP_TUNNEL_ECN: skb is dropped according to
 	 * RFC 6040 4.2, see __INET_ECN_decapsulate() for detail.
-- 
2.47.1

[PATCH net-next v3 2/2] net: bridge: add skb drop reasons to the most common drop points

[Radu Rendec]

The bridge input code may drop frames for various reasons and at various
points in the ingress handling logic. Currently kfree_skb() is used
everywhere, and therefore no drop reason is specified. Add drop reasons
to the most common drop points.

Drop reasons are not added exhaustively to the entire bridge code. The
intention is to incrementally add drop reasons to the rest of the bridge
code in follow up patches.

Signed-off-by: Radu Rendec <rrendec@redhat.com>
---
 include/net/dropreason-core.h | 12 ++++++++++++
 net/bridge/br_forward.c       | 16 ++++++++++++----
 net/bridge/br_input.c         | 20 +++++++++++++++-----
 3 files changed, 39 insertions(+), 9 deletions(-)

diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
index 6e32106d72294..3a6602f379783 100644
--- a/include/net/dropreason-core.h
+++ b/include/net/dropreason-core.h
@@ -111,6 +111,8 @@
 	FN(TUNNEL_TXINFO)		\
 	FN(LOCAL_MAC)			\
 	FN(ARP_PVLAN_DISABLE)		\
+	FN(MAC_IEEE_MAC_CONTROL)	\
+	FN(BRIDGE_INGRESS_STP_STATE)	\
 	FNe(MAX)
 
 /**
@@ -520,6 +522,16 @@ enum skb_drop_reason {
 	 * enabled.
 	 */
 	SKB_DROP_REASON_ARP_PVLAN_DISABLE,
+	/**
+	 * @SKB_DROP_REASON_MAC_IEEE_MAC_CONTROL: the destination MAC address
+	 * is an IEEE MAC Control address.
+	 */
+	SKB_DROP_REASON_MAC_IEEE_MAC_CONTROL,
+	/**
+	 * @SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE: the STP state of the
+	 * ingress bridge port does not allow frames to be forwarded.
+	 */
+	SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE,
 	/**
 	 * @SKB_DROP_REASON_MAX: the maximum of core drop reasons, which
 	 * shouldn't be used as a real 'reason' - only for tracing code gen
diff --git a/net/bridge/br_forward.c b/net/bridge/br_forward.c
index e19b583ff2c6d..29097e984b4f7 100644
--- a/net/bridge/br_forward.c
+++ b/net/bridge/br_forward.c
@@ -201,6 +201,7 @@ void br_flood(struct net_bridge *br, struct sk_buff *skb,
 	      enum br_pkt_type pkt_type, bool local_rcv, bool local_orig,
 	      u16 vid)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NO_TX_TARGET;
 	struct net_bridge_port *prev = NULL;
 	struct net_bridge_port *p;
 
@@ -234,8 +235,11 @@ void br_flood(struct net_bridge *br, struct sk_buff *skb,
 			continue;
 
 		prev = maybe_deliver(prev, p, skb, local_orig);
-		if (IS_ERR(prev))
+		if (IS_ERR(prev)) {
+			reason = PTR_ERR(prev) == -ENOMEM ? SKB_DROP_REASON_NOMEM :
+				 SKB_DROP_REASON_NOT_SPECIFIED;
 			goto out;
+		}
 	}
 
 	if (!prev)
@@ -249,7 +253,7 @@ void br_flood(struct net_bridge *br, struct sk_buff *skb,
 
 out:
 	if (!local_rcv)
-		kfree_skb(skb);
+		kfree_skb_reason(skb, reason);
 }
 
 #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
@@ -289,6 +293,7 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 			struct net_bridge_mcast *brmctx,
 			bool local_rcv, bool local_orig)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NO_TX_TARGET;
 	struct net_bridge_port *prev = NULL;
 	struct net_bridge_port_group *p;
 	bool allow_mode_include = true;
@@ -329,8 +334,11 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 		}
 
 		prev = maybe_deliver(prev, port, skb, local_orig);
-		if (IS_ERR(prev))
+		if (IS_ERR(prev)) {
+			reason = PTR_ERR(prev) == -ENOMEM ? SKB_DROP_REASON_NOMEM :
+				 SKB_DROP_REASON_NOT_SPECIFIED;
 			goto out;
+		}
 delivered:
 		if ((unsigned long)lport >= (unsigned long)port)
 			p = rcu_dereference(p->next);
@@ -349,6 +357,6 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
 
 out:
 	if (!local_rcv)
-		kfree_skb(skb);
+		kfree_skb_reason(skb, reason);
 }
 #endif
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index ceaa5a89b947f..232133a0fd21c 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -75,6 +75,7 @@ static int br_pass_frame_up(struct sk_buff *skb, bool promisc)
 /* note: already called with rcu_read_lock */
 int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	struct net_bridge_port *p = br_port_get_rcu(skb->dev);
 	enum br_pkt_type pkt_type = BR_PKT_UNICAST;
 	struct net_bridge_fdb_entry *dst = NULL;
@@ -96,8 +97,10 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
 	if (br_mst_is_enabled(br)) {
 		state = BR_STATE_FORWARDING;
 	} else {
-		if (p->state == BR_STATE_DISABLED)
+		if (p->state == BR_STATE_DISABLED) {
+			reason = SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE;
 			goto drop;
+		}
 
 		state = p->state;
 	}
@@ -155,8 +158,10 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
 		}
 	}
 
-	if (state == BR_STATE_LEARNING)
+	if (state == BR_STATE_LEARNING) {
+		reason = SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE;
 		goto drop;
+	}
 
 	BR_INPUT_SKB_CB(skb)->brdev = br->dev;
 	BR_INPUT_SKB_CB(skb)->src_port_isolated = !!(p->flags & BR_ISOLATED);
@@ -223,7 +228,7 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
 out:
 	return 0;
 drop:
-	kfree_skb(skb);
+	kfree_skb_reason(skb, reason);
 	goto out;
 }
 EXPORT_SYMBOL_GPL(br_handle_frame_finish);
@@ -324,6 +329,7 @@ static int br_process_frame_type(struct net_bridge_port *p,
  */
 static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 {
+	enum skb_drop_reason reason = SKB_DROP_REASON_NOT_SPECIFIED;
 	struct net_bridge_port *p;
 	struct sk_buff *skb = *pskb;
 	const unsigned char *dest = eth_hdr(skb)->h_dest;
@@ -331,8 +337,10 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 	if (unlikely(skb->pkt_type == PACKET_LOOPBACK))
 		return RX_HANDLER_PASS;
 
-	if (!is_valid_ether_addr(eth_hdr(skb)->h_source))
+	if (!is_valid_ether_addr(eth_hdr(skb)->h_source)) {
+		reason = SKB_DROP_REASON_MAC_INVALID_SOURCE;
 		goto drop;
+	}
 
 	skb = skb_share_check(skb, GFP_ATOMIC);
 	if (!skb)
@@ -374,6 +382,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 			return RX_HANDLER_PASS;
 
 		case 0x01:	/* IEEE MAC (Pause) */
+			reason = SKB_DROP_REASON_MAC_IEEE_MAC_CONTROL;
 			goto drop;
 
 		case 0x0E:	/* 802.1AB LLDP */
@@ -423,8 +432,9 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
 
 		return nf_hook_bridge_pre(skb, pskb);
 	default:
+		reason = SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE;
 drop:
-		kfree_skb(skb);
+		kfree_skb_reason(skb, reason);
 	}
 	return RX_HANDLER_CONSUMED;
 }
-- 
2.47.1

Re: [PATCH net-next v3 1/2] net: vxlan: rename SKB_DROP_REASON_VXLAN_NO_REMOTE

[Ido Schimmel]

On Thu, Dec 19, 2024 at 11:36:05AM -0500, Radu Rendec wrote:
> The SKB_DROP_REASON_VXLAN_NO_REMOTE skb drop reason was introduced in
> the specific context of vxlan. As it turns out, there are similar cases
> when a packet needs to be dropped in other parts of the network stack,
> such as the bridge module.
> 
> Rename SKB_DROP_REASON_VXLAN_NO_REMOTE and give it a more generic name,
> so that it can be used in other parts of the network stack. This is not
> a functional change, and the numeric value of the drop reason even
> remains unchanged.
> 
> Signed-off-by: Radu Rendec <rrendec@redhat.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Re: [PATCH net-next v3 2/2] net: bridge: add skb drop reasons to the most common drop points

[Ido Schimmel]

On Thu, Dec 19, 2024 at 11:36:06AM -0500, Radu Rendec wrote:
> The bridge input code may drop frames for various reasons and at various
> points in the ingress handling logic. Currently kfree_skb() is used
> everywhere, and therefore no drop reason is specified. Add drop reasons
> to the most common drop points.
> 
> Drop reasons are not added exhaustively to the entire bridge code. The
> intention is to incrementally add drop reasons to the rest of the bridge
> code in follow up patches.
> 
> Signed-off-by: Radu Rendec <rrendec@redhat.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Re: [PATCH net-next v3 1/2] net: vxlan: rename SKB_DROP_REASON_VXLAN_NO_REMOTE

[Nikolay Aleksandrov]

On 12/19/24 18:36, Radu Rendec wrote:
> The SKB_DROP_REASON_VXLAN_NO_REMOTE skb drop reason was introduced in
> the specific context of vxlan. As it turns out, there are similar cases
> when a packet needs to be dropped in other parts of the network stack,
> such as the bridge module.
> 
> Rename SKB_DROP_REASON_VXLAN_NO_REMOTE and give it a more generic name,
> so that it can be used in other parts of the network stack. This is not
> a functional change, and the numeric value of the drop reason even
> remains unchanged.
> 
> Signed-off-by: Radu Rendec <rrendec@redhat.com>
> ---
>  drivers/net/vxlan/vxlan_core.c | 4 ++--
>  drivers/net/vxlan/vxlan_mdb.c  | 2 +-
>  include/net/dropreason-core.h  | 6 +++---
>  3 files changed, 6 insertions(+), 6 deletions(-)
> 

Acked-by: Nikolay Aleksandrov <razor@blackwall.org>

Re: [PATCH net-next v3 2/2] net: bridge: add skb drop reasons to the most common drop points

[Nikolay Aleksandrov]

On 12/19/24 18:36, Radu Rendec wrote:
> The bridge input code may drop frames for various reasons and at various
> points in the ingress handling logic. Currently kfree_skb() is used
> everywhere, and therefore no drop reason is specified. Add drop reasons
> to the most common drop points.
> 
> Drop reasons are not added exhaustively to the entire bridge code. The
> intention is to incrementally add drop reasons to the rest of the bridge
> code in follow up patches.
> 
> Signed-off-by: Radu Rendec <rrendec@redhat.com>
> ---
>  include/net/dropreason-core.h | 12 ++++++++++++
>  net/bridge/br_forward.c       | 16 ++++++++++++----
>  net/bridge/br_input.c         | 20 +++++++++++++++-----
>  3 files changed, 39 insertions(+), 9 deletions(-)
> 


Acked-by: Nikolay Aleksandrov <razor@blackwall.org>

Re: [PATCH net-next v3 0/2] net/bridge: Add skb drop reasons to the most common drop points

[patchwork-bot+netdevbpf]

Hello:

This series was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 19 Dec 2024 11:36:04 -0500 you wrote:
> The bridge input code may drop frames for various reasons and at various
> points in the ingress handling logic. Currently kfree_skb() is used
> everywhere, and therefore no drop reason is specified. Add drop reasons
> to the most common drop points.
> 
> The purpose of this series is to address the most common drop points on
> the bridge ingress path. It does not exhaustively add drop reasons to
> the entire bridge code. The intention here is to incrementally add drop
> reasons to the rest of the bridge code in follow up patches.
> 
> [...]

Here is the summary with links:
  - [net-next,v3,1/2] net: vxlan: rename SKB_DROP_REASON_VXLAN_NO_REMOTE
    https://git.kernel.org/netdev/net-next/c/46e0ccfb88f0
  - [net-next,v3,2/2] net: bridge: add skb drop reasons to the most common drop points
    https://git.kernel.org/netdev/net-next/c/623e43c2f502

You are awesome, thank you!
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