On Tue, 2024-12-10 at 11:18 +0200, Nikolay Aleksandrov wrote:
> 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 <rren...@redhat.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.
Sure, thanks for reviewing! Please see my 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?
Yes, Ido had a similar suggestion [1], so it's clear that it must be
renamed. I will go with SKB_DROP_REASON_BRIDGE_INGRESS_STP_STATE in the
next version, unless you have a better idea.
> > + /**
> > + * 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.
I will follow Ido's suggestion [2] and rename SKB_DROP_REASON_VXLAN_NO_REMOTE
to SKB_DROP_REASON_NO_TX_TARGET, and then use that.
But it will only cover the case when there are no errors, so I still
need a different reason for the error case. I looked, and I couldn't
find an existing one that's close enough, so I think I should create a
new one. How about SKB_DROP_REASON_TX_ERROR? I would not use "BRIDGE"
in the name because I'm thinking it may be reused elsewhere, outside
the bridge module.
> > }
> >
> > #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;
> > }
[1] https://lore.kernel.org/bridge/Z1sLyqZQCjbcCOde@shredder/
[2] https://lore.kernel.org/bridge/Z1sUsSFfBC9GoiIA@shredder/
--
Best regards,
Radu
