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Message-ID: <2283799b-e1fe-42c2-aecc-50c4ae1f9afa@blackwall.org>
Date: Tue, 10 Dec 2024 11:18:06 +0200
From: Nikolay Aleksandrov <razor@...ckwall.org>
To: Radu Rendec <rrendec@...hat.com>, Roopa Prabhu <roopa@...dia.com>
Cc: bridge@...ts.linux.dev, netdev@...r.kernel.org,
Simon Horman <horms@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next] net/bridge: Add skb drop reasons to the most
common drop points
On 12/9/24 00:18, 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.
>
> The purpose of this patch 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 patch 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_BRIDGE_NO_EGRESS_PORT in br_multicast_flood(). I could
> not find an easy way to make a crafted packet get there.
> * SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD 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_PORT_NFWD - 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_PORT_NFWD - 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_BRIDGE_NO_EGRESS_PORT - 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
>
> Signed-off-by: Radu Rendec <rrendec@...hat.com>
> ---
> include/net/dropreason-core.h | 18 ++++++++++++++++++
> net/bridge/br_forward.c | 4 ++--
> net/bridge/br_input.c | 24 +++++++++++++++---------
> 3 files changed, 35 insertions(+), 11 deletions(-)
>
Hi,
Thanks for working on this, a few comments below.
> diff --git a/include/net/dropreason-core.h b/include/net/dropreason-core.h
> index c29282fabae6..1f2ae5b387c1 100644
> --- a/include/net/dropreason-core.h
> +++ b/include/net/dropreason-core.h
> @@ -108,6 +108,9 @@
> FN(TUNNEL_TXINFO) \
> FN(LOCAL_MAC) \
> FN(ARP_PVLAN_DISABLE) \
> + FN(MAC_IEEE_MAC_CONTROL) \
> + FN(BRIDGE_INGRESS_PORT_NFWD) \
> + FN(BRIDGE_NO_EGRESS_PORT) \
> FNe(MAX)
>
> /**
> @@ -502,6 +505,21 @@ 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_PORT_NFWD: the STP state of the
> + * ingress bridge port does not allow frames to be forwarded.
> + */
> + SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD,
Since this is used only when the port state causes the packet to drop, why not
rename it to something that suggests it was the state?
> + /**
> + * SKB_DROP_REASON_BRIDGE_NO_EGRESS_PORT: no eligible egress port was
> + * found while attempting to flood the frame.
> + */
> + SKB_DROP_REASON_BRIDGE_NO_EGRESS_PORT,
> /**
> * @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 e19b583ff2c6..e33e2f4fc3d9 100644
> --- a/net/bridge/br_forward.c
> +++ b/net/bridge/br_forward.c
> @@ -249,7 +249,7 @@ void br_flood(struct net_bridge *br, struct sk_buff *skb,
>
> out:
> if (!local_rcv)
> - kfree_skb(skb);
> + kfree_skb_reason(skb, SKB_DROP_REASON_BRIDGE_NO_EGRESS_PORT);
This is not entirely correct, we can get here if we had an error forwarding
the packet to some port, but it may already have been forwarded to others.
The reason should distinguish between those two cases.
> }
>
> #ifdef CONFIG_BRIDGE_IGMP_SNOOPING
> @@ -349,6 +349,6 @@ void br_multicast_flood(struct net_bridge_mdb_entry *mdst,
>
> out:
> if (!local_rcv)
> - kfree_skb(skb);
> + kfree_skb_reason(skb, SKB_DROP_REASON_BRIDGE_NO_EGRESS_PORT);
Same comment as above (br_flood).
> }
> #endif
> diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
> index ceaa5a89b947..fc00e172e1e1 100644
> --- a/net/bridge/br_input.c
> +++ b/net/bridge/br_input.c
> @@ -96,8 +96,10 @@ 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)
> - goto drop;
> + if (p->state == BR_STATE_DISABLED) {
> + kfree_skb_reason(skb, SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD);
> + return 0;
> + }
>
> state = p->state;
> }
> @@ -155,8 +157,10 @@ int br_handle_frame_finish(struct net *net, struct sock *sk, struct sk_buff *skb
> }
> }
>
> - if (state == BR_STATE_LEARNING)
> - goto drop;
> + if (state == BR_STATE_LEARNING) {
> + kfree_skb_reason(skb, SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD);
> + return 0;
> + }>
> BR_INPUT_SKB_CB(skb)->brdev = br->dev;
> BR_INPUT_SKB_CB(skb)->src_port_isolated = !!(p->flags & BR_ISOLATED);
> @@ -331,8 +335,10 @@ 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))
> - goto drop;
> + if (!is_valid_ether_addr(eth_hdr(skb)->h_source)) {
> + kfree_skb_reason(skb, SKB_DROP_REASON_MAC_INVALID_SOURCE);
> + return RX_HANDLER_CONSUMED;
> + }
>
> skb = skb_share_check(skb, GFP_ATOMIC);
> if (!skb)
> @@ -374,7 +380,8 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
> return RX_HANDLER_PASS;
>
> case 0x01: /* IEEE MAC (Pause) */
> - goto drop;
> + kfree_skb_reason(skb, SKB_DROP_REASON_MAC_IEEE_MAC_CONTROL);
> + return RX_HANDLER_CONSUMED;
>
> case 0x0E: /* 802.1AB LLDP */
> fwd_mask |= p->br->group_fwd_mask;
> @@ -423,8 +430,7 @@ static rx_handler_result_t br_handle_frame(struct sk_buff **pskb)
>
> return nf_hook_bridge_pre(skb, pskb);
> default:
> -drop:
> - kfree_skb(skb);
> + kfree_skb_reason(skb, SKB_DROP_REASON_BRIDGE_INGRESS_PORT_NFWD);
> }
> return RX_HANDLER_CONSUMED;
> }
Cheers,
Nik
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