Le ven. 6 nov. 2026 à 09:16, <[email protected]> a écrit :
>
> Thank you for your contribution! Sashiko AI review found 1 potential
> issue to consider:
> - [Medium] selftests: net: tun: UDP tunnel GSO tests still fail on
> big-endian hosts
> --
>
> commit 19b0a422177cb62b0357c401d17b939feb10dca3
> Author: Eric Dumazet <[email protected]>
>
> selftests: net: tuntap: write UDP tunnel offsets in little endian
>
> This commit converts the outer_th_offset and inner_nh_offset fields of
> struct virtio_net_hdr_v1_hash_tunnel to little-endian in the tuntap
> selftests while leaving the base virtio_net_hdr_v1 fields in host byte
> order.
>
> > diff --git a/tools/testing/selftests/net/tuntap_helpers.h
> > b/tools/testing/selftests/net/tuntap_helpers.h
> > index ecad83fae1582..dc85cd9bc0aec 100644
> > --- a/tools/testing/selftests/net/tuntap_helpers.h
> > +++ b/tools/testing/selftests/net/tuntap_helpers.h
>
> [ ... ]
>
> > @@ -375,11 +377,14 @@ static inline int
> > build_virtio_net_hdr_v1_hash_tunnel(uint8_t *buf, bool is_tap,
> > inner_iphlen = (inner_family == AF_INET) ? sizeof(struct iphdr) :
> > sizeof(struct ipv6hdr);
> >
> > - vh_tunnel->outer_th_offset = eth_hlen + outer_iphlen;
> > - vh_tunnel->inner_nh_offset = vh_tunnel->outer_th_offset + ETH_HLEN +
> > - GENEVE_HLEN + sizeof(struct udphdr);
> > + outer_th = eth_hlen + outer_iphlen;
> > + inner_nh = outer_th + ETH_HLEN + GENEVE_HLEN + sizeof(struct udphdr);
> >
> > - vh->csum_start = vh_tunnel->inner_nh_offset + inner_iphlen;
> > + /* The tunnel offsets are always little endian. */
> > + vh_tunnel->outer_th_offset = htole16(outer_th);
> > + vh_tunnel->inner_nh_offset = htole16(inner_nh);
> > +
> > + vh->csum_start = inner_nh + inner_iphlen;
> > vh->csum_offset = __builtin_offsetof(struct udphdr, check);
> > vh->flags = VIRTIO_NET_HDR_F_NEEDS_CSUM;
> > vh->hdr_len = hdr_len;
>
> [Severity: Medium]
> Will the UDP tunnel GSO tests still fail on big-endian hosts because the
> kernel hardcodes little_endian = true when delegating the base header fields
> in virtio_net_hdr_tnl_to_skb() and virtio_net_hdr_tnl_from_skb()?
Right, the kernel treats the whole tunnel header as little endian, so
the tests need TUNSETVNETLE and little endian accesses for all fields,
not only the tunnel offsets. I will do that in the separate selftests
series.
>
> In tools/testing/selftests/net/tun.c, tun_open() does not set TUNSETVNETLE,
> so tun_vnet_is_little_endian() is false and __tun_vnet_hdr_get() reads
> hdr_len, csum_start, and csum_offset in host order. However, when
> tun_vnet_hdr_tnl_to_skb() calls virtio_net_hdr_tnl_to_skb() with
> little_endian = false:
>
> include/linux/virtio_net.h:virtio_net_hdr_tnl_to_skb() {
> ...
> inner_th = __virtio16_to_cpu(little_endian, hdr->csum_start);
> inner_nh = le16_to_cpu(vhdr->inner_nh_offset);
> outer_th = le16_to_cpu(vhdr->outer_th_offset);
> if (outer_th < outer_l3min ||
> inner_nh < outer_th + sizeof(struct udphdr) ||
> inner_th < inner_nh + inner_l3min)
> return -EINVAL;
>
> /* Let the basic parsing deal with plain GSO features. */
> ret = __virtio_net_hdr_to_skb(skb, hdr, true,
> hdr->gso_type & ~gso_tunnel_type);
> if (ret)
> return ret;
>
> if (!virtio_net_tnl_offsets_ok(skb, has_eth, outer_isv6, outer_th))
> return -EINVAL;
> ...
> }
>
> Because __virtio_net_hdr_to_skb() is called with little_endian hardcoded to
> true instead of passing little_endian, it byte-swaps the host-order
> csum_start, csum_offset, and gso_size on big-endian hosts. That causes
> __virtio_net_hdr_to_skb() to return -EINVAL (either in pskb_may_pull() or the
> skb->csum_offset check) before virtio_net_tnl_offsets_ok() is reached in
> tun_vnet_udptnl_proto, tun_vnet_udptnl_proto_l3, and tun_vnet_udptnl.
>
> Similarly, on the receive path in virtio_net_hdr_tnl_from_skb():
>
> include/linux/virtio_net.h:virtio_net_hdr_tnl_from_skb() {
> ...
> /* Let the basic parsing deal with plain GSO features. */
> skb_shinfo(skb)->gso_type &= ~tnl_gso_type;
> ret = virtio_net_hdr_from_skb(skb, hdr, true, false, vlan_hlen);
> skb_shinfo(skb)->gso_type |= tnl_gso_type;
> ...
> }
>
> virtio_net_hdr_from_skb() is also called with little_endian hardcoded to
> true, writing hdr->gso_size in little-endian while recv_gso_packet in
> tools/testing/selftests/net/tun.c compares vh->gso_size against host-order
> variant->gso_size.
>
> --
> Sashiko AI review ·
> https://sashiko.dev/#/patchset/[email protected]?part=8
