On Tue, Oct 13, 2026 at 06:58:28AM -0400, Michael S. Tsirkin wrote:
> 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 does this: checksum at ingress, except in a narrow list
> of specified known good cases.
>
> Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr")
I forgot.
Reported-by: Paulos Yibelo <[email protected]>
Reported-by: Chris Arges <[email protected]>
> Michael S. Tsirkin (4):
> net: add ip4_parse()
> net: use ip4_parse() in receive validation
> net: resolve uncommon partial checksums at ingress
> net: account for ingress-resolved virtio net hdr state
>
> drivers/net/tap.c | 4 +-
> drivers/net/tun.c | 44 +++++++-
> drivers/net/virtio_net.c | 2 +-
> include/linux/ip.h | 24 +++++
> include/linux/virtio_net.h | 161 ++++++++++++++++++++++++----
> net/bridge/br_netfilter_hooks.c | 15 +--
> net/ipv4/ip_input.c | 13 +--
> net/ipv4/netfilter/nf_reject_ipv4.c | 13 +--
> net/packet/af_packet.c | 4 +-
> 9 files changed, 228 insertions(+), 52 deletions(-)
>
> --
> MST
>
