[PATCH net 0/3] net: virtio: validate outer protocol of UDP tunnel GSO packets

[Eric Dumazet <edumazet@kernel.org>]

virtio_net_hdr_tnl_to_skb() does not check that a UDP tunnel GSO
packet really has an outer IPv4/IPv6 header matching the declared
tunnel type. A guest, or any tap writer, can send a frame with another
outer ethertype (NSH in the report), and the GSO stack then builds
segments with skb->data before skb->head. The host crashes in
skb_under_panic() as soon as a header is pushed.

Patch 1 adds the missing check. Ethernet frames can carry VLAN tags
before the outer IP header; for IFF_TUN, skb->protocol is provided
by the caller.

Patch 2 fixes a selftest helper computing UDP checksums over a length
in network byte order.

Patch 3 adds tun selftests: valid outer IPv4 frames (plain and VLAN
tagged) are accepted, mismatched or non-IP outer headers are rejected.

Eric Dumazet (3):
  net: virtio: validate outer protocol of UDP tunnel GSO packets
  selftests: net: tuntap: fix UDP checksum length in
    build_udp_packet_csum()
  selftests: net: tun: test outer protocol of UDP tunnel GSO packets

 include/linux/virtio_net.h                   |  28 ++++
 tools/testing/selftests/net/tun.c            | 130 +++++++++++++++++++
 tools/testing/selftests/net/tuntap_helpers.h |   2 +-
 3 files changed, 159 insertions(+), 1 deletion(-)


base-commit: 647b81ddefc6364290e67bf33c89d54971f8995e
-- 
2.53.0