On Tue, Oct 13, 2026 at 06:58:41AM -0400, Michael S. Tsirkin wrote: > A virtio net header can place CHECKSUM_PARTIAL at any in-packet > offset. If that state is retained, later checksum completion can > modify the packet after protocol processing has made decisions from it. > > Let's fix that: let's validate csum_start and csum_offset and only keep > CHECKSUM_PARTIAL when csum_start and csum_offset match a parsed TCP or > UDP header, while handling VLAN headers, IPv4 options and IPv6 extension > headers. Complete other non-GSO checksums immediately, before any > protocol processing runs. > > We can't easily "complete the checksum" for GSO we don't recognize - GSO > assumes knowledge of the protocol. We could segment ignoring the > checksum then do whatever csum_start and csum_offset say, but that > seems like an overkill for something that should happen. > > UDP tunnel headers get the same handling on the inner header. > > Packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are unaffected. > > Suggested-by: Willem de Bruijn <[email protected]> > Signed-off-by: Michael S. Tsirkin <[email protected]> > Assisted-by: LLM
I forgot reported-by tags: Reported-by: Paulos Yibelo <[email protected]> Reported-by: Chris Arges <[email protected]> > --- > include/linux/virtio_net.h | 151 ++++++++++++++++++++++++++++++++----- > 1 file changed, 133 insertions(+), 18 deletions(-) > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > index d6466f96cdd00..b181183118b3a 100644 > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -5,7 +5,11 @@ > #include <linux/if_vlan.h> > #include <linux/ip.h> > #include <linux/ipv6.h> > +#include <linux/netdevice.h> > #include <linux/udp.h> > +#include <net/gso.h> > +#include <net/ip.h> > +#include <net/ipv6.h> > #include <net/tcp.h> > #include <uapi/linux/tcp.h> > #include <uapi/linux/virtio_net.h> > @@ -48,15 +52,111 @@ static inline int virtio_net_hdr_set_proto(struct > sk_buff *skb, > return 0; > } > > +/* Does checksum metadata match a known TCP or UDP header? */ > +static inline bool > +virtio_net_csum_partial_ok_at_offset(struct sk_buff *skb, u8 hdr_gso_type, > + unsigned int nhoff, __be16 proto) > +{ > + unsigned int thoff; > + int ip_proto; > + > + if (proto == htons(ETH_P_IP)) { > + const struct iphdr *iph = ip4_parse(skb, nhoff, &thoff); > + > + if (!iph || ip_is_fragment(iph)) > + return false; > + ip_proto = iph->protocol; > + } else if (proto == htons(ETH_P_IPV6)) { > + const struct ipv6hdr *iph; > + int flags = 0; > + > + if (!pskb_may_pull(skb, nhoff + sizeof(*iph))) > + return false; > + iph = (const void *)(skb->data + nhoff); > + if (iph->version != 6) > + return false; > + thoff = nhoff + sizeof(*iph); > + ip_proto = iph->nexthdr; > + if (ip_proto != IPPROTO_TCP && ip_proto != IPPROTO_UDP) { > + thoff = nhoff; > + ip_proto = ipv6_find_hdr(skb, &thoff, -1, NULL, > + &flags); > + if (ip_proto < 0 || flags & IP6_FH_F_FRAG) > + return false; > + } > + } else { > + return false; > + } > + > + if (skb_checksum_start_offset(skb) != thoff) > + return false; > + > + switch (ip_proto) { > + case IPPROTO_TCP: > + if (skb->csum_offset != offsetof(struct tcphdr, check) || > + !pskb_may_pull(skb, thoff + sizeof(struct tcphdr))) > + return false; > + break; > + case IPPROTO_UDP: > + if (skb->csum_offset != offsetof(struct udphdr, check) || > + !pskb_may_pull(skb, thoff + sizeof(struct udphdr))) > + return false; > + break; > + default: > + return false; > + } > + > + switch (hdr_gso_type & ~VIRTIO_NET_HDR_GSO_ECN) { > + case VIRTIO_NET_HDR_GSO_NONE: > + return true; > + case VIRTIO_NET_HDR_GSO_TCPV4: > + return proto == htons(ETH_P_IP) && ip_proto == IPPROTO_TCP; > + case VIRTIO_NET_HDR_GSO_TCPV6: > + return proto == htons(ETH_P_IPV6) && ip_proto == IPPROTO_TCP; > + case VIRTIO_NET_HDR_GSO_UDP: > + case VIRTIO_NET_HDR_GSO_UDP_L4: > + return ip_proto == IPPROTO_UDP; > + default: > + return false; > + } > +} > + > +static inline bool > +virtio_net_csum_partial_ok(struct sk_buff *skb, u8 hdr_gso_type) > +{ > + unsigned int nhoff; > + __be16 proto; > + > + if (skb->dev->type == ARPHRD_ETHER) { > + if (!pskb_may_pull(skb, ETH_HLEN)) > + return false; > + nhoff = ETH_HLEN; > + proto = eth_hdr(skb)->h_proto; > + if (eth_type_vlan(proto)) { > + proto = __vlan_get_protocol(skb, proto, &nhoff); > + if (!proto) > + return false; > + } > + } else { > + nhoff = skb_network_offset(skb); > + proto = skb->protocol; > + } > + > + return virtio_net_csum_partial_ok_at_offset(skb, hdr_gso_type, nhoff, > + proto); > +} > + > static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > const struct virtio_net_hdr *hdr, > - bool little_endian, u8 hdr_gso_type) > + bool little_endian, u8 hdr_gso_type, > + bool need_csum_check) > { > - unsigned int nh_min_len = sizeof(struct iphdr); > + typeof(skb->transport_header) old_transport = skb->transport_header; > unsigned int gso_type = 0; > unsigned int thlen = 0; > unsigned int p_off = 0; > unsigned int ip_proto; > + bool csum_partial_ok = true; > > if (hdr_gso_type != VIRTIO_NET_HDR_GSO_NONE) { > switch (hdr_gso_type & ~VIRTIO_NET_HDR_GSO_ECN) { > @@ -69,7 +169,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff > *skb, > gso_type = SKB_GSO_TCPV6; > ip_proto = IPPROTO_TCP; > thlen = sizeof(struct tcphdr); > - nh_min_len = sizeof(struct ipv6hdr); > break; > case VIRTIO_NET_HDR_GSO_UDP: > gso_type = SKB_GSO_UDP; > @@ -104,11 +203,11 @@ static inline int __virtio_net_hdr_to_skb(struct > sk_buff *skb, > > if (!skb_partial_csum_set(skb, start, off)) > return -EINVAL; > - if (skb_transport_offset(skb) < nh_min_len) > - return -EINVAL; > + if (need_csum_check) > + csum_partial_ok = > + virtio_net_csum_partial_ok(skb, hdr_gso_type); > > - nh_min_len = skb_transport_offset(skb); > - p_off = nh_min_len + thlen; > + p_off = skb_transport_offset(skb) + thlen; > if (!pskb_may_pull(skb, p_off)) > return -EINVAL; > } else if (gso_type) { > @@ -158,8 +257,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff > *skb, > case SKB_GSO_UDP_L4: > if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM)) > return -EINVAL; > - if (skb->csum_offset != offsetof(struct udphdr, check)) > - return -EINVAL; > if (skb->len - p_off > gso_size * UDP_MAX_SEGMENTS) > return -EINVAL; > if (gso_type != SKB_GSO_UDP_L4) > @@ -167,10 +264,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff > *skb, > break; > case SKB_GSO_TCPV4: > case SKB_GSO_TCPV6: > - if (skb->ip_summed == CHECKSUM_PARTIAL && > - skb->csum_offset != offsetof(struct tcphdr, check)) > - return -EINVAL; > - > BUILD_BUG_ON(TCP_MIN_GSO_SIZE * GSO_MAX_SEGS < > GSO_MAX_SIZE); > gso_size = max(gso_size, TCP_MIN_GSO_SIZE); > break; > @@ -191,6 +284,17 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff > *skb, > } > } > > + if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && !csum_partial_ok) { > + int err; > + > + if (skb_is_gso(skb)) > + return -EINVAL; > + > + err = skb_checksum_help(skb); > + skb->transport_header = old_transport; > + return err; > + } > + > return 0; > } > > @@ -198,7 +302,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff > *skb, > const struct virtio_net_hdr *hdr, > bool little_endian) > { > - return __virtio_net_hdr_to_skb(skb, hdr, little_endian, hdr->gso_type); > + return __virtio_net_hdr_to_skb(skb, hdr, little_endian, > + hdr->gso_type, true); > } > > /* This function must be called after virtio_net_hdr_from_skb(). */ > @@ -293,6 +398,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > unsigned int inner_nh, outer_th, inner_th; > unsigned int inner_l3min, outer_l3min; > u8 gso_inner_type, gso_tunnel_type; > + __be16 inner_proto; > bool outer_isv6, inner_isv6; > int ret; > > @@ -334,7 +440,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > /* Let the basic parsing deal with plain GSO features. */ > ret = __virtio_net_hdr_to_skb(skb, hdr, true, > - hdr->gso_type & ~gso_tunnel_type); > + hdr->gso_type & ~gso_tunnel_type, false); > if (ret) > return ret; > > @@ -352,8 +458,8 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > return -EINVAL; > } > > - skb_set_inner_protocol(skb, inner_isv6 ? htons(ETH_P_IPV6) : > - htons(ETH_P_IP)); > + inner_proto = inner_isv6 ? htons(ETH_P_IPV6) : htons(ETH_P_IP); > + skb_set_inner_protocol(skb, inner_proto); > if (hdr->flags & VIRTIO_NET_HDR_F_UDP_TUNNEL_CSUM) { > if (!tnl_csum_negotiated) > return -EINVAL; > @@ -368,7 +474,16 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > skb->inner_mac_header = inner_nh + skb_headroom(skb); > skb->transport_header = outer_th + skb_headroom(skb); > skb->encapsulation = 1; > - return 0; > + > + if (virtio_net_csum_partial_ok_at_offset(skb, gso_inner_type, inner_nh, > + inner_proto)) > + return 0; > + > + if (skb_is_gso(skb)) > + return -EINVAL; > + > + ret = skb_checksum_help(skb); > + return ret ?: 1; > } > > /* Checksum-related fields validation for the driver */ > -- > MST >
