On 2026-10-19 08:03:00, Michael S. Tsirkin wrote: > > As reported first by Paulos Yibelo <[email protected]> (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: > > These are definitely net material (and seem to be too big for stable, > or I would recommend backporting there, too): > > 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 > > These are cleanups, can be deferred to net-next, too: > > 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 > > > Changes since v2: > > virtio_net: parse tunnel csum_start little-endian > - new patch. correctly parsing the header is a dependency > of validating it, otherwise i do not know what to validate > > net: account for ingress-resolved virtio net hdr state > - make rx_csum_sw counter 64 bit so it won't wrap > (spotted by LLM review) > > net: resolve uncommon partial checksums at ingress > - tunnel fixes to bugs noticed by Willem de Bruijn and > Chris Arges > - restore the csum_offset checks as suggested by Willem > - parse csum_start in the tunnel header little-endian like > the rest of it (spotted by LLM review) > > net: add a sysctl to opt out of virtio net hdr checksum validation > - the knob is no longer writable by root inside a user > namespace: changing it now requires capable(CAP_NET_ADMIN) > suggested by Willem de Bruijn > > net: add ip4_parse() > - comment converted to kernel-doc format (Willem de Bruijn) > > um: vector: honor virtio net hdr conversion failures > - commit log tweaks > > New patch: > um: vector: trim skbs before verifying the header > found by code review > > Somewhat tested, tunnel also tested now, um part compiled only >
I was able to run my tests and can confirm no more KASAN errors. I did not test the um patches. Tested-by: Chris Arges <[email protected]> > > Michael S. Tsirkin (8): > 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 > virtio_net: parse tunnel csum_start little-endian > 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 | 19 ++ > 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 | 27 +++ > include/linux/virtio_net.h | 272 ++++++++++++++++++++++- > 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 | 60 +++++ > net/ipv4/ip_input.c | 13 +- > net/ipv4/netfilter/nf_reject_ipv4.c | 13 +- > net/packet/af_packet.c | 4 +- > 16 files changed, 445 insertions(+), 43 deletions(-) > > -- > MST >
