kernel/linux.git/net/bridge/br_forward.c, branch v7.2-rc2

net: bridge: use atomic ops to read/change p->flags (I)

2026-06-13T01:03:46+00:00

Use test_bit() in net/bridge/br_arp_nd_proxy.c, net/bridge/br_fdb.c and net/bridge/br_forward.c. Use READ_ONCE(p->flags) in br_recalculate_neigh_suppress_enabled() as we test two bits at once. Signed-off-by: Eric Dumazet Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20260611203453.3067462-4-edumazet@google.com Signed-off-by: Jakub Kicinski

bridge: Add selective forwarding of gratuitous neighbor announcements

2026-05-14T10:42:11+00:00

The existing neighbor suppression unconditionally suppresses gratuitous ARPs and unsolicited Neighbor Advertisements, which prevents fast mobility of hosts between VTEPs. Add the neigh_forward_grat option to allow selective control of gratuitous neighbor announcements. When neigh_suppress is enabled but neigh_forward_grat is disabled (default), gratuitous announcements are suppressed. When neigh_forward_grat is enabled, gratuitous announcements are forwarded while regular neighbor discovery remains suppressed. The implementation provides per-output-port control by: 1. Adding a 'grat_arp' flag to BR_INPUT_SKB_CB to mark gratuitous ARPs and unsolicited NAs. 2. Setting both grat_arp and proxyarp_replied flags in br_do_proxy_suppress_arp() and br_do_suppress_nd() when gratuitous packets are detected. 3. Checking neigh_forward_grat per output port during flooding: - For gratuitous ARPs/NAs: suppress unless the output port has neigh_forward_grat enabled. - For regular ARPs/NDs: maintain existing behavior. This allows gratuitous announcements from any input port to be selectively forwarded based on each output port's individual neigh_forward_grat setting, enabling gratuitous neighbor announcements to be flooded to the VXLAN fabric. Regular neighbor discovery (ARP requests, NS queries, solicited replies) remains controlled by neigh_suppress and is unaffected. Reviewed-by: Ido Schimmel Reviewed-by: Petr Machata Signed-off-by: Danielle Ratson Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20260511065936.4173106-4-danieller@nvidia.com Signed-off-by: Paolo Abeni

net: bridge: fix use-after-free due to MST port state bypass

2025-11-06T15:32:17+00:00

syzbot reported[1] a use-after-free when deleting an expired fdb. It is due to a race condition between learning still happening and a port being deleted, after all its fdbs have been flushed. The port's state has been toggled to disabled so no learning should happen at that time, but if we have MST enabled, it will bypass the port's state, that together with VLAN filtering disabled can lead to fdb learning at a time when it shouldn't happen while the port is being deleted. VLAN filtering must be disabled because we flush the port VLANs when it's being deleted which will stop learning. This fix adds a check for the port's vlan group which is initialized to NULL when the port is getting deleted, that avoids the port state bypass. When MST is enabled there would be a minimal new overhead in the fast-path because the port's vlan group pointer is cache-hot. [1] https://syzkaller.appspot.com/bug?extid=dd280197f0f7ab3917be Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode") Reported-by: syzbot+dd280197f0f7ab3917be@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/69088ffa.050a0220.29fc44.003d.GAE@google.com/ Signed-off-by: Nikolay Aleksandrov Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20251105111919.1499702-2-razor@blackwall.org Signed-off-by: Jakub Kicinski

bridge: Redirect to backup port when port is administratively down

2025-08-15T00:45:36+00:00

If a backup port is configured for a bridge port, the bridge will redirect known unicast traffic towards the backup port when the primary port is administratively up but without a carrier. This is useful, for example, in MLAG configurations where a system is connected to two switches and there is a peer link between both switches. The peer link serves as the backup port in case one of the switches loses its connection to the multi-homed system. In order to avoid flooding when the primary port loses its carrier, the bridge does not flush dynamic FDB entries pointing to the port upon STP disablement, if the port has a backup port. The above means that known unicast traffic destined to the primary port will be blackholed when the port is put administratively down, until the FDB entries pointing to it are aged-out. Given that the current behavior is quite weird and unlikely to be depended on by anyone, amend the bridge to redirect to the backup port also when the primary port is administratively down and not only when it does not have a carrier. The change is motivated by a report from a user who expected traffic to be redirected to the backup port when the primary port was put administratively down while debugging a network issue. Reviewed-by: Petr Machata Signed-off-by: Ido Schimmel Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20250812080213.325298-2-idosch@nvidia.com Signed-off-by: Jakub Kicinski

net: bridge: add skb drop reasons to the most common drop points

2024-12-23T18:11:04+00:00

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 Reviewed-by: Ido Schimmel Acked-by: Nikolay Aleksandrov Link: https://patch.msgid.link/20241219163606.717758-3-rrendec@redhat.com Signed-off-by: Jakub Kicinski

net: bridge: mst: Check vlan state for egress decision

2024-07-15T12:40:28+00:00

If a port is blocking in the common instance but forwarding in an MST instance, traffic egressing the bridge will be dropped because the state of the common instance is overriding that of the MST instance. Fix this by skipping the port state check in MST mode to allow checking the vlan state via br_allowed_egress(). This is similar to what happens in br_handle_frame_finish() when checking ingress traffic, which was introduced in the change below. Fixes: ec7328b59176 ("net: bridge: mst: Multiple Spanning Tree (MST) mode") Signed-off-by: Elliot Ayrey Acked-by: Nikolay Aleksandrov Signed-off-by: David S. Miller

net: bridge: fix corrupted ethernet header on multicast-to-unicast

2024-05-08T09:37:57+00:00

The change from skb_copy to pskb_copy unfortunately changed the data copying to omit the ethernet header, since it was pulled before reaching this point. Fix this by calling __skb_push/pull around pskb_copy. Fixes: 59c878cbcdd8 ("net: bridge: fix multicast-to-unicast with fraglist GSO") Signed-off-by: Felix Fietkau Acked-by: Nikolay Aleksandrov Signed-off-by: David S. Miller

net: bridge: fix multicast-to-unicast with fraglist GSO

2024-05-01T10:44:10+00:00

Calling skb_copy on a SKB_GSO_FRAGLIST skb is not valid, since it returns an invalid linearized skb. This code only needs to change the ethernet header, so pskb_copy is the right function to call here. Fixes: 6db6f0eae605 ("bridge: multicast to unicast") Signed-off-by: Felix Fietkau Acked-by: Paolo Abeni Acked-by: Nikolay Aleksandrov Signed-off-by: David S. Miller

net: bridge: use DEV_STATS_INC()

2023-09-19T11:35:15+00:00

syzbot/KCSAN reported data-races in br_handle_frame_finish() [1] This function can run from multiple cpus without mutual exclusion. Adopt SMP safe DEV_STATS_INC() to update dev->stats fields. Handles updates to dev->stats.tx_dropped while we are at it. [1] BUG: KCSAN: data-race in br_handle_frame_finish / br_handle_frame_finish read-write to 0xffff8881374b2178 of 8 bytes by interrupt on cpu 1: br_handle_frame_finish+0xd4f/0xef0 net/bridge/br_input.c:189 br_nf_hook_thresh+0x1ed/0x220 br_nf_pre_routing_finish_ipv6+0x50f/0x540 NF_HOOK include/linux/netfilter.h:304 [inline] br_nf_pre_routing_ipv6+0x1e3/0x2a0 net/bridge/br_netfilter_ipv6.c:178 br_nf_pre_routing+0x526/0xba0 net/bridge/br_netfilter_hooks.c:508 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline] nf_hook_bridge_pre net/bridge/br_input.c:272 [inline] br_handle_frame+0x4c9/0x940 net/bridge/br_input.c:417 __netif_receive_skb_core+0xa8a/0x21e0 net/core/dev.c:5417 __netif_receive_skb_one_core net/core/dev.c:5521 [inline] __netif_receive_skb+0x57/0x1b0 net/core/dev.c:5637 process_backlog+0x21f/0x380 net/core/dev.c:5965 __napi_poll+0x60/0x3b0 net/core/dev.c:6527 napi_poll net/core/dev.c:6594 [inline] net_rx_action+0x32b/0x750 net/core/dev.c:6727 __do_softirq+0xc1/0x265 kernel/softirq.c:553 run_ksoftirqd+0x17/0x20 kernel/softirq.c:921 smpboot_thread_fn+0x30a/0x4a0 kernel/smpboot.c:164 kthread+0x1d7/0x210 kernel/kthread.c:388 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304 read-write to 0xffff8881374b2178 of 8 bytes by interrupt on cpu 0: br_handle_frame_finish+0xd4f/0xef0 net/bridge/br_input.c:189 br_nf_hook_thresh+0x1ed/0x220 br_nf_pre_routing_finish_ipv6+0x50f/0x540 NF_HOOK include/linux/netfilter.h:304 [inline] br_nf_pre_routing_ipv6+0x1e3/0x2a0 net/bridge/br_netfilter_ipv6.c:178 br_nf_pre_routing+0x526/0xba0 net/bridge/br_netfilter_hooks.c:508 nf_hook_entry_hookfn include/linux/netfilter.h:144 [inline] nf_hook_bridge_pre net/bridge/br_input.c:272 [inline] br_handle_frame+0x4c9/0x940 net/bridge/br_input.c:417 __netif_receive_skb_core+0xa8a/0x21e0 net/core/dev.c:5417 __netif_receive_skb_one_core net/core/dev.c:5521 [inline] __netif_receive_skb+0x57/0x1b0 net/core/dev.c:5637 process_backlog+0x21f/0x380 net/core/dev.c:5965 __napi_poll+0x60/0x3b0 net/core/dev.c:6527 napi_poll net/core/dev.c:6594 [inline] net_rx_action+0x32b/0x750 net/core/dev.c:6727 __do_softirq+0xc1/0x265 kernel/softirq.c:553 do_softirq+0x5e/0x90 kernel/softirq.c:454 __local_bh_enable_ip+0x64/0x70 kernel/softirq.c:381 __raw_spin_unlock_bh include/linux/spinlock_api_smp.h:167 [inline] _raw_spin_unlock_bh+0x36/0x40 kernel/locking/spinlock.c:210 spin_unlock_bh include/linux/spinlock.h:396 [inline] batadv_tt_local_purge+0x1a8/0x1f0 net/batman-adv/translation-table.c:1356 batadv_tt_purge+0x2b/0x630 net/batman-adv/translation-table.c:3560 process_one_work kernel/workqueue.c:2630 [inline] process_scheduled_works+0x5b8/0xa30 kernel/workqueue.c:2703 worker_thread+0x525/0x730 kernel/workqueue.c:2784 kthread+0x1d7/0x210 kernel/kthread.c:388 ret_from_fork+0x48/0x60 arch/x86/kernel/process.c:147 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:304 value changed: 0x00000000000d7190 -> 0x00000000000d7191 Reported by Kernel Concurrency Sanitizer on: CPU: 0 PID: 14848 Comm: kworker/u4:11 Not tainted 6.6.0-rc1-syzkaller-00236-gad8a69f361b9 #0 Fixes: 1c29fc4989bc ("[BRIDGE]: keep track of received multicast packets") Reported-by: syzbot Signed-off-by: Eric Dumazet Cc: Roopa Prabhu Cc: Nikolay Aleksandrov Cc: bridge@lists.linux-foundation.org Acked-by: Nikolay Aleksandrov Link: https://lore.kernel.org/r/20230918091351.1356153-1-edumazet@google.com Signed-off-by: Paolo Abeni

bridge: Add backup nexthop ID support

2023-07-19T09:53:49+00:00

Add a new bridge port attribute that allows attaching a nexthop object ID to an skb that is redirected to a backup bridge port with VLAN tunneling enabled. Specifically, when redirecting a known unicast packet, read the backup nexthop ID from the bridge port that lost its carrier and set it in the bridge control block of the skb before forwarding it via the backup port. Note that reading the ID from the bridge port should not result in a cache miss as the ID is added next to the 'backup_port' field that was already accessed. After this change, the 'state' field still stays on the first cache line, together with other data path related fields such as 'flags and 'vlgrp': struct net_bridge_port { struct net_bridge * br; /* 0 8 */ struct net_device * dev; /* 8 8 */ netdevice_tracker dev_tracker; /* 16 0 */ struct list_head list; /* 16 16 */ long unsigned int flags; /* 32 8 */ struct net_bridge_vlan_group * vlgrp; /* 40 8 */ struct net_bridge_port * backup_port; /* 48 8 */ u32 backup_nhid; /* 56 4 */ u8 priority; /* 60 1 */ u8 state; /* 61 1 */ u16 port_no; /* 62 2 */ /* --- cacheline 1 boundary (64 bytes) --- */ [...] } __attribute__((__aligned__(8))); When forwarding an skb via a bridge port that has VLAN tunneling enabled, check if the backup nexthop ID stored in the bridge control block is valid (i.e., not zero). If so, instead of attaching the pre-allocated metadata (that only has the tunnel key set), allocate a new metadata, set both the tunnel key and the nexthop object ID and attach it to the skb. By default, do not dump the new attribute to user space as a value of zero is an invalid nexthop object ID. The above is useful for EVPN multihoming. When one of the links composing an Ethernet Segment (ES) fails, traffic needs to be redirected towards the host via one of the other ES peers. For example, if a host is multihomed to three different VTEPs, the backup port of each ES link needs to be set to the VXLAN device and the backup nexthop ID needs to point to an FDB nexthop group that includes the IP addresses of the other two VTEPs. The VXLAN driver will extract the ID from the metadata of the redirected skb, calculate its flow hash and forward it towards one of the other VTEPs. If the ID does not exist, or represents an invalid nexthop object, the VXLAN driver will drop the skb. This relieves the bridge driver from the need to validate the ID. Signed-off-by: Ido Schimmel Acked-by: Nikolay Aleksandrov Signed-off-by: David S. Miller