[PATCH net-next v2 0/7] more virtio-net csum hardening

["Michael S. Tsirkin" <mst@redhat.com>]

As reported first by Paulos Yibelo <habte.yibelo@gmail.com> (after which
others, credited below, found more ways the bug can affect users):

allowing untrusted hardware to specify csum start/offset for
CHECKSUM_PARTIAL was not a good idea, because, if it edits the packet
outside the actual checksum, and depending on the setup, the networking
stack could be looking at the packet both before and after the edit, and
seeing different results.

Previously, commit 6785011f8b16 ("ipv4: validate checksum_start before
completing checksum") validated all known instances where this
causes the most grief, but the real fix is to make sure
that either only actual checksum fields are ever edited,
or the checksum is completed before the net stack looks at it,
so it is always consistent.


This basically goes back to
what we did before f43798c27684 ("tun: Allow GSO using virtio_net_hdr"),
except in a narrow list of specified known good cases.


Summary of the patchset:
  net: account for ingress-resolved virtio net hdr state
	- accounting, not the fix itself, dependency of the next one
  net: resolve uncommon partial checksums at ingress
	- fix itself
  net: add a sysctl to opt out of virtio net hdr checksum validation
	- reducing risk of the fix by adding a sysctl to disable it
  net: add ip4_parse()
  virtio_net: cleanup protocol calculation
	- cleanup resulting code duplication
	 (kept separate to simplify backporting)

Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")

Changes since v1:
	- reorder patches to fix bisectability, addressing
	  a comment by Björn Töpel.
	- code refactoring, different patch splitup,
	  a sysctl knob to disable as suggested by Willem de Bruijn.
	- fix a bunch of minor issues spotted by LLMs


Michael S. Tsirkin (7):
  net: account for ingress-resolved virtio net hdr state
  um: vector: honor virtio net hdr conversion failures
  um: vector: trim skbs before verifying the header
  net: resolve uncommon partial checksums at ingress
  net: add a sysctl to opt out of virtio net hdr checksum validation
  net: add ip4_parse()
  virtio_net: cleanup protocol calculation

 Documentation/admin-guide/sysctl/net.rst |  15 ++
 arch/um/drivers/vector_kern.c            |   6 +-
 arch/um/drivers/vector_transports.c      |   4 +-
 drivers/net/tap.c                        |   4 +-
 drivers/net/tun.c                        |  41 +++-
 drivers/net/virtio_net.c                 |   2 +-
 include/linux/ip.h                       |  24 +++
 include/linux/virtio_net.h               | 249 ++++++++++++++++++++++-
 include/net/netns/core.h                 |   1 +
 net/bridge/br_netfilter_hooks.c          |  15 +-
 net/core/dev.c                           |   6 +
 net/core/net_namespace.c                 |   1 +
 net/core/sysctl_net_core.c               |  54 +++++
 net/ipv4/ip_input.c                      |  13 +-
 net/ipv4/netfilter/nf_reject_ipv4.c      |  13 +-
 net/packet/af_packet.c                   |   4 +-
 16 files changed, 404 insertions(+), 48 deletions(-)

-- 
MST