[Qemu-devel] [Bug 1758091] [NEW] vmxnet3 unable to send IPv6 ESP packets

[Thomas Jansen]

Public bug reported:

My vmxnet3 network driver (in a closed source custom OS) is unable to
send network packets that are structured as follows: Ethernet-
Header(IPv6-Header(ESP(encrypted data))). I can verify that the packet
is sent in the VM but is dropped in qemu. I first encountered this
problem on qemu 2.10.1 but master is affected as well. After some debug
printing in qemu I could identify the following call chain as being
problematic:

eth_is_ip6_extension_header_type
eth_parse_ipv6_hdr
net_tx_pkt_parse_headers
net_tx_pkt_parse
vmxnet3_process_tx_queue

The problem seems to be the definition of the ESP header
(https://en.wikipedia.org/wiki/IPsec#Encapsulating_Security_Payload)
that does not follow the standard IPv6 extension header format starting
with next type and length. Thus the parsed ext_hdr in eth_parse_ipv6_hdr
does not contain valid data, in particular the length will contain bogus
data and lead to a info->full_hdr_len that is larger than the packet
itself and the loop would then try to read beyond the end of the packet.

Using the e1000 driver I can send these packets. My guess is that the
net_tx_pkt_parse function is not called in that case.

My guess for a fix would be to remove "case IP6_ESP:" from
eth_is_ip6_extension_header_type and not regard the ESP header as a IPv6
extension header. In a quick test this seems to fix the problem. But
that should be verified by someone who is familiar with the code.

** Affects: qemu
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1758091

Title:
  vmxnet3 unable to send IPv6 ESP packets

Status in QEMU:
  New

Bug description:
  My vmxnet3 network driver (in a closed source custom OS) is unable to
  send network packets that are structured as follows: Ethernet-
  Header(IPv6-Header(ESP(encrypted data))). I can verify that the packet
  is sent in the VM but is dropped in qemu. I first encountered this
  problem on qemu 2.10.1 but master is affected as well. After some
  debug printing in qemu I could identify the following call chain as
  being problematic:

  eth_is_ip6_extension_header_type
  eth_parse_ipv6_hdr
  net_tx_pkt_parse_headers
  net_tx_pkt_parse
  vmxnet3_process_tx_queue

  The problem seems to be the definition of the ESP header
  (https://en.wikipedia.org/wiki/IPsec#Encapsulating_Security_Payload)
  that does not follow the standard IPv6 extension header format
  starting with next type and length. Thus the parsed ext_hdr in
  eth_parse_ipv6_hdr does not contain valid data, in particular the
  length will contain bogus data and lead to a info->full_hdr_len that
  is larger than the packet itself and the loop would then try to read
  beyond the end of the packet.

  Using the e1000 driver I can send these packets. My guess is that the
  net_tx_pkt_parse function is not called in that case.

  My guess for a fix would be to remove "case IP6_ESP:" from
  eth_is_ip6_extension_header_type and not regard the ESP header as a
  IPv6 extension header. In a quick test this seems to fix the problem.
  But that should be verified by someone who is familiar with the code.

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