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[80.230.79.236]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49fda8f04f7sm2635925e9.0.2026.09.21.15.11.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 21 Sep 2026 15:11:44 -0700 (PDT) Date: Mon, 21 Sep 2026 18:11:39 -0400 From: "Michael S. Tsirkin" To: Paulos Yibelo Cc: netdev@vger.kernel.org, richard@nod.at, anton.ivanov@cambridgegreys.com, johannes@sipsolutions.net, willemdebruijn.kernel@gmail.com, jasowangio@gmail.com, eperezma@redhat.com, xuanzhuo@linux.alibaba.com, andrew+netdev@lunn.ch, pablo@netfilter.org, fw@strlen.de, phil@nwl.cc, razor@blackwall.org, idosch@nvidia.com, dsahern@kernel.org, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, linux-um@lists.infradead.org, virtualization@lists.linux.dev, netfilter-devel@vger.kernel.org, coreteam@netfilter.org, bridge@lists.linux.dev, linux-kernel@vger.kernel.org Subject: Re: [PATCH net v5 1/2] net: validate virtio checksum start after network header Message-ID: <20260921181115-mutt-send-email-mst@kernel.org> References: <20260920004733.6473-1-habte.yibelo@gmail.com> <20260921025341.44846-1-habte.yibelo@gmail.com> <20260921025341.44846-2-habte.yibelo@gmail.com> Precedence: bulk X-Mailing-List: bridge@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20260921025341.44846-2-habte.yibelo@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: gCiyW5i-EXLL9HCR9Lo6oToyO2dqnqyT5m7Zwa13f68_1790028706 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Sun, Sep 20, 2026 at 10:53:40PM -0400, Paulos Yibelo wrote: > __virtio_net_hdr_to_skb() rejects a CHECKSUM_PARTIAL start smaller than > an estimated minimum network-header length. Its input offsets are relative > to skb->data. > > Using skb_network_offset() here is unsafe. TUN/TAP, virtio-net, and UML > parse a received virtio header before skb->network_header is established. > On an skb with headroom, the resulting negative offset enlarges the > apparent distance to the transport header and can admit a checksum start > inside the network header. > > Pass the data-relative L3 offset to the converter explicitly. IFF_TUN uses > zero, AF_PACKET supplies its established network offset, and Ethernet > receive paths parse Ethernet and nested VLAN headers with > skb_header_pointer(), without changing skb state. Use the same origin for > tunnel-offset validation, and make UML propagate conversion failures. > > This does not require a virtual-machine guest. A TUN or TAP device with > virtio-net header support is sufficient to reach these paths. > > Fixes: 49d14b54a527 ("net: test for not too small csum_start in virtio_net_hdr_to_skb()") > Fixes: a2fb4bc4e2a6 ("net: implement virtio helpers to handle UDP GSO tunneling.") > Reported-by: Paulos Yibelo > Link: https://lore.kernel.org/netdev/20260920004733.6473-2-habte.yibelo@gmail.com/ > Cc: stable@vger.kernel.org > Signed-off-by: Paulos Yibelo v4 had assisted-by tag? same q for patch 2. > --- > Changes in v5: > - Replace the not-yet-established skb network-header offset with an > explicit data-relative L3 origin. > - Cover all in-tree callers, including Ethernet/VLAN receive paths, > tunnel metadata, and UML error propagation. > - Drop the prior Acked-by and Reviewed-by tags because the code changed. > > Changes in v4: > - State that a TUN device is sufficient and no guest is required, as > noted by Michael S. Tsirkin. > > Changes in v3: > - Keep the network-relative comparison on one line for readability, as > requested by David Ahern. > > Changes in v2: > - Make nh_min_len an int and remove the casts, as suggested by Michael S. > Tsirkin. > > arch/um/drivers/vector_transports.c | 10 +++- > drivers/net/tun_vnet.h | 28 ++++++++++- > drivers/net/virtio_net.c | 8 ++- > include/linux/virtio_net.h | 76 +++++++++++++++++++++++------ > net/packet/af_packet.c | 6 ++- > 5 files changed, 106 insertions(+), 22 deletions(-) > > diff --git a/arch/um/drivers/vector_transports.c b/arch/um/drivers/vector_transports.c > index ddd127ee9..79bc05fc6 100644 > --- a/arch/um/drivers/vector_transports.c > +++ b/arch/um/drivers/vector_transports.c > @@ -197,6 +197,7 @@ static int raw_verify_header( > uint8_t *header, struct sk_buff *skb, struct vector_private *vp) > { > struct virtio_net_hdr *vheader = (struct virtio_net_hdr *) header; > + int network_offset; > > if ((vheader->gso_type != VIRTIO_NET_HDR_GSO_NONE) && > (vp->req_size != 65536)) { > @@ -209,8 +210,13 @@ static int raw_verify_header( > if ((vheader->flags & VIRTIO_NET_HDR_F_DATA_VALID) > 0) > return 1; > > - virtio_net_hdr_to_skb(skb, vheader, virtio_legacy_is_little_endian()); > - return 0; > + network_offset = virtio_net_hdr_get_l3_offset(skb, vheader); > + if (network_offset < 0) > + return network_offset; > + > + return virtio_net_hdr_to_skb(skb, vheader, > + virtio_legacy_is_little_endian(), > + network_offset); > } > > static bool get_uint_param( > diff --git a/drivers/net/tun_vnet.h b/drivers/net/tun_vnet.h > index f4c652b1f..1c83c359d 100644 > --- a/drivers/net/tun_vnet.h > +++ b/drivers/net/tun_vnet.h > @@ -177,10 +177,27 @@ static inline int tun_vnet_hdr_put(int sz, struct iov_iter *iter, > return __tun_vnet_hdr_put(sz, 0, iter, hdr); > } > > +static inline int > +tun_vnet_hdr_get_l3_offset(unsigned int flags, const struct sk_buff *skb, > + const struct virtio_net_hdr *hdr) > +{ > + if ((flags & TUN_TYPE_MASK) != IFF_TAP) > + return 0; > + > + return virtio_net_hdr_get_l3_offset(skb, hdr); > +} > + > static inline int tun_vnet_hdr_to_skb(unsigned int flags, struct sk_buff *skb, > const struct virtio_net_hdr *hdr) > { > - return virtio_net_hdr_to_skb(skb, hdr, tun_vnet_is_little_endian(flags)); > + int network_offset = tun_vnet_hdr_get_l3_offset(flags, skb, hdr); > + > + if (network_offset < 0) > + return network_offset; > + > + return virtio_net_hdr_to_skb(skb, hdr, > + tun_vnet_is_little_endian(flags), > + network_offset); > } > > /* > @@ -199,10 +216,17 @@ tun_vnet_hdr_tnl_to_skb(unsigned int flags, netdev_features_t features, > struct sk_buff *skb, > const struct virtio_net_hdr_v1_hash_tunnel *hdr) > { > + const struct virtio_net_hdr *vnet_hdr = (const struct virtio_net_hdr *)hdr; > + int network_offset = tun_vnet_hdr_get_l3_offset(flags, skb, vnet_hdr); > + > + if (network_offset < 0) > + return network_offset; > + > return virtio_net_hdr_tnl_to_skb(skb, hdr, > features & NETIF_F_GSO_UDP_TUNNEL, > features & NETIF_F_GSO_UDP_TUNNEL_CSUM, > - tun_vnet_is_little_endian(flags)); > + tun_vnet_is_little_endian(flags), > + network_offset); > } > > static inline int tun_vnet_hdr_from_skb(unsigned int flags, > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index e34c52d05..059eeb18e 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2502,6 +2502,7 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue * > { > struct virtio_net_common_hdr *hdr; > struct net_device *dev = vi->dev; > + int network_offset; > > hdr = skb_vnet_common_hdr(skb); > if (dev->features & NETIF_F_RXHASH && vi->has_rss_hash_report) > @@ -2515,9 +2516,12 @@ static void virtnet_receive_done(struct virtnet_info *vi, struct receive_queue * > goto frame_err; > } > > - if (virtio_net_hdr_tnl_to_skb(skb, &hdr->tnl_hdr, vi->rx_tnl, > + network_offset = virtio_net_hdr_get_l3_offset(skb, &hdr->hdr); > + if (network_offset < 0 || > + virtio_net_hdr_tnl_to_skb(skb, &hdr->tnl_hdr, vi->rx_tnl, > vi->rx_tnl_csum, > - virtio_is_little_endian(vi->vdev))) { > + virtio_is_little_endian(vi->vdev), > + network_offset)) { > net_warn_ratelimited("%s: bad gso: type: %x, size: %u, flags %x tunnel %d tnl csum %d\n", > dev->name, hdr->hdr.gso_type, > hdr->hdr.gso_size, hdr->hdr.flags, > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > index c381b916c..a4c005796 100644 > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -48,11 +48,49 @@ static inline int virtio_net_hdr_set_proto(struct sk_buff *skb, > return 0; > } > > +/* > + * Return the L3 offset of an Ethernet frame starting at skb->data. > + * The offset is unused without NEEDS_CSUM, so avoid parsing and return zero. > + */ > +static inline int > +virtio_net_hdr_get_l3_offset(const struct sk_buff *skb, > + const struct virtio_net_hdr *hdr) > +{ > + unsigned int parse_depth = VLAN_MAX_DEPTH; > + const struct ethhdr *eth; > + struct ethhdr ethbuf; > + __be16 protocol; > + int depth = ETH_HLEN; > + > + if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM)) > + return 0; > + > + eth = skb_header_pointer(skb, 0, sizeof(ethbuf), ðbuf); > + if (!eth) > + return -EINVAL; > + > + protocol = eth->h_proto; > + while (eth_type_vlan(protocol)) { > + const struct vlan_hdr *vh; > + struct vlan_hdr vhdr; > + > + vh = skb_header_pointer(skb, depth, sizeof(vhdr), &vhdr); > + if (!vh || !--parse_depth) > + return -EINVAL; > + > + protocol = vh->h_vlan_encapsulated_proto; > + depth += VLAN_HLEN; > + } > + > + return depth; > +} > + > 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, > + int network_offset) > { > - unsigned int nh_min_len = sizeof(struct iphdr); > + int nh_min_len = sizeof(struct iphdr); > unsigned int gso_type = 0; > unsigned int thlen = 0; > unsigned int p_off = 0; > @@ -98,16 +136,20 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > u32 start = __virtio16_to_cpu(little_endian, hdr->csum_start); > u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); > u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16)); > + int transport_offset; > > if (!pskb_may_pull(skb, needed)) > return -EINVAL; > > if (!skb_partial_csum_set(skb, start, off)) > return -EINVAL; > - if (skb_transport_offset(skb) < nh_min_len) > + > + transport_offset = skb_transport_offset(skb); > + if (transport_offset < nh_min_len || network_offset < 0 || > + network_offset > transport_offset - nh_min_len) > return -EINVAL; > > - nh_min_len = skb_transport_offset(skb); > + nh_min_len = transport_offset; > p_off = nh_min_len + thlen; > if (!pskb_may_pull(skb, p_off)) > return -EINVAL; > @@ -206,9 +248,11 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, > const struct virtio_net_hdr *hdr, > - bool little_endian) > + bool little_endian, > + int network_offset) > { > - 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, > + network_offset); > } > > /* This function must be called after virtio_net_hdr_from_skb(). */ > @@ -287,7 +331,7 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb, > return 0; > } > > -static inline unsigned int virtio_l3min(bool is_ipv6) > +static inline int virtio_l3min(bool is_ipv6) > { > return is_ipv6 ? sizeof(struct ipv6hdr) : sizeof(struct iphdr); > } > @@ -297,18 +341,19 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > const struct virtio_net_hdr_v1_hash_tunnel *vhdr, > bool tnl_hdr_negotiated, > bool tnl_csum_negotiated, > - bool little_endian) > + bool little_endian, int network_offset) > { > const struct virtio_net_hdr *hdr = (const struct virtio_net_hdr *)vhdr; > - unsigned int inner_nh, outer_th, inner_th; > - unsigned int inner_l3min, outer_l3min; > u8 gso_inner_type, gso_tunnel_type; > bool outer_isv6, inner_isv6; > + int inner_nh, outer_th, inner_th; > + int inner_l3min, outer_l3min; > int ret; > > gso_tunnel_type = hdr->gso_type & VIRTIO_NET_HDR_GSO_UDP_TUNNEL; > if (!gso_tunnel_type) > - return virtio_net_hdr_to_skb(skb, hdr, little_endian); > + return virtio_net_hdr_to_skb(skb, hdr, little_endian, > + network_offset); > > /* Tunnel not supported/negotiated, but the hdr asks for it. */ > if (!tnl_hdr_negotiated) > @@ -332,19 +377,22 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > outer_isv6 = gso_tunnel_type & VIRTIO_NET_HDR_GSO_UDP_TUNNEL_IPV6; > inner_isv6 = gso_inner_type == VIRTIO_NET_HDR_GSO_TCPV6; > inner_l3min = virtio_l3min(inner_isv6); > - outer_l3min = ETH_HLEN + virtio_l3min(outer_isv6); > + outer_l3min = virtio_l3min(outer_isv6); > > 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 || > + if (network_offset < 0 || > + outer_th < outer_l3min || > + network_offset > 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); > + hdr->gso_type & ~gso_tunnel_type, > + network_offset); > if (ret) > return ret; > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c > index 50cae32ae..04c80e23d 100644 > --- a/net/packet/af_packet.c > +++ b/net/packet/af_packet.c > @@ -2901,7 +2901,8 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg) > } > > if (has_vnet_hdr) { > - if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le())) { > + if (virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le(), > + skb_network_offset(skb))) { > tp_len = -EINVAL; > goto tpacket_error; > } > @@ -3103,7 +3104,8 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len) > packet_parse_headers(skb, sock); > > if (vnet_hdr_sz) { > - err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le()); > + err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le(), > + skb_network_offset(skb)); > if (err) > goto out_free; > len += vnet_hdr_sz; > -- > 2.46.0