[Bug 294666] VLAN packets through bridge and dummynet gets VLAN ID set to 0

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=294666

            Bug ID: 294666
           Summary: VLAN packets through bridge and dummynet gets VLAN ID
                    set to 0
           Product: Base System
           Version: 15.0-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: kern
          Assignee: bugs@FreeBSD.org
          Reporter: groos@xiplink.com

Simple bridge setup with ipfw and dummynet:

root@satsim:~ # ifconfig bridge0
bridge0: flags=1008843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST,LOWER_UP> metric
0 mtu 9000
        options=10<VLAN_HWTAGGING>
        ether 58:9c:fc:10:9f:8e
        id 00:00:00:00:00:00 priority 32768 hellotime 2 fwddelay 15
        maxage 20 holdcnt 6 proto rstp maxaddr 2000 timeout 1200
        root id 00:00:00:00:00:00 priority 32768 ifcost 0 port 0
        bridge flags=0<>
        member: em2 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
                port 3 priority 128 path cost 2000 vlan protocol 802.1q
        member: em1 flags=143<LEARNING,DISCOVER,AUTOEDGE,AUTOPTP>
                port 2 priority 128 path cost 2000 vlan protocol 802.1q
        groups: bridge
        nd6 options=9<PERFORMNUD,IFDISABLED>

root@satsim:~ # ipfw show
00100 363624 43841638 pipe 1 ip from any to any out via em1
00100 363630 43842757 pipe 1 ip from any to any out via em2
65535      0        0 count ip from any to any not // orphaned dynamic states
counter
65535 766733 89810147 allow ip from any to any

root@satsim:~ # ipfw pipe 1 show
00001: 300.000 Mbit/s  300 ms burst 0 
q131073 1000 KB 0 flows (1 buckets) sched 65537 weight 0 lmax 0 pri 0 droptail
 sched 65537 type FIFO flags 0x0 0 buckets 1 active
BKT Prot ___Source IP/port____ ____Dest. IP/port____ Tot_pkt/bytes Pkt/Byte Drp
  0 ip           0.0.0.0/0             0.0.0.0/0     730004 98236299  0    0  
0

VLAN packets egressing have their VLAN ID's incorrectly set to 0:

10:20:29.755829 02:f8:36:ad:3c:e2 > 02:64:f0:31:29:45, ethertype 802.1Q
(0x8100), length 114: vlan 0, p 0, ethertype IPv4 (0x0800), 10.98.252.204 >
10.98.252.205: ESP(spi=0xc6a48616,seq=0x634), length 76

Removing the ipfw pipe rules result in the original, correct VLAN ID on the
egressing packets.

The following seems to fix it:

diff --git a/sys/netpfil/ipfw/ip_dn_io.c b/sys/netpfil/ipfw/ip_dn_io.c
index 03116cb0641c..af256b1a76a7 100644
--- a/sys/netpfil/ipfw/ip_dn_io.c
+++ b/sys/netpfil/ipfw/ip_dn_io.c
@@ -848,6 +848,22 @@ dummynet_send(struct mbuf *m)
                case DIR_OUT | PROTO_LAYER2 | PROTO_IPV6:
                case DIR_OUT | PROTO_LAYER2: /* DN_TO_ETH_OUT: */
                        MPASS(ifp != NULL);
+                       /*
+                        * If the packet carries a VLAN tag in M_VLANTAG,
+                        * encode it into the Ethernet header before passing
+                        * to ether_output_frame().  ether_set_pcp() (called
+                        * from ether_output_frame) would otherwise re-insert
+                        * a VLAN tag with VID 0, discarding the original VID.
+                        */
+                       if (m->m_flags & M_VLANTAG) {
+                               m = ether_vlanencap_proto(m,
+                                   m->m_pkthdr.ether_vtag, ETHERTYPE_VLAN);
+                               if (m == NULL)
+                                       break;
+                               m->m_flags &= ~M_VLANTAG;
+                       }
+
                        ether_output_frame(ifp, m);
                        break;

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