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[Stable-9.1.3,64/65] net/dump: Correctly compute Ethernet packet offset

Message ID 20250207115501.2278106-6-mjt@tls.msk.ru (mailing list archive)
State New
Headers show
Series Patch Round-up for stable 9.1.3, freeze on 2025-02-06 (frozen) | expand

Commit Message

Michael Tokarev Feb. 7, 2025, 11:54 a.m. UTC 
From: Laurent Vivier <lvivier@redhat.com>

When a packet is sent with QEMU_NET_PACKET_FLAG_RAW by QEMU it
never includes virtio-net header even if qemu_get_vnet_hdr_len()
is not 0, and filter-dump is not managing this case.

The only user of QEMU_NET_PACKET_FLAG_RAW is announce_self,
we can show the problem using it and tcpddump:

- QEMU parameters:

  .. -monitor stdio \
     -netdev bridge,id=netdev0,br=virbr0 \
     -device virtio-net,mac=9a:2b:2c:2d:2e:2f,netdev=netdev0 \
     -object filter-dump,netdev=netdev0,file=log.pcap,id=pcap0

- HMP command:

  (qemu) announce_self

- TCP dump:

  $ tcpdump -nxr log.pcap

  without the fix:

    08:00:06:04:00:03 > 2e:2f:80:35:00:01, ethertype Unknown (0x9a2b), length 50:
         0x0000:  2c2d 2e2f 0000 0000 9a2b 2c2d 2e2f 0000
         0x0010:  0000 0000 0000 0000 0000 0000 0000 0000
         0x0020:  0000 0000

  with the fix:

    ARP, Reverse Request who-is 9a:2b:2c:2d:2e:2f tell 9a:2b:2c:2d:2e:2f, length 46
         0x0000:  0001 0800 0604 0003 9a2b 2c2d 2e2f 0000
         0x0010:  0000 9a2b 2c2d 2e2f 0000 0000 0000 0000
         0x0020:  0000 0000 0000 0000 0000 0000 0000

Fixes: 481c52320a26 ("net: Strip virtio-net header when dumping")
Cc: akihiko.odaki@daynix.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
Reviewed-by: Michael Tokarev <mjt@tls.msk.ru>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
(cherry picked from commit c6a1b591a68b4d7230d6c3f56965e18080d737e5)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
diff mbox series

Patch

diff --git a/net/dump.c b/net/dump.c
index 956e34a123..42ab8d7716 100644
--- a/net/dump.c
+++ b/net/dump.c
@@ -155,7 +155,8 @@  static ssize_t filter_dump_receive_iov(NetFilterState *nf, NetClientState *sndr,
 {
     NetFilterDumpState *nfds = FILTER_DUMP(nf);
 
-    dump_receive_iov(&nfds->ds, iov, iovcnt, qemu_get_vnet_hdr_len(nf->netdev));
+    dump_receive_iov(&nfds->ds, iov, iovcnt, flags & QEMU_NET_PACKET_FLAG_RAW ?
+                     0 : qemu_get_vnet_hdr_len(nf->netdev));
     return 0;
 }