From: Mathieu Tortuyaux mtortuyaux@microsoft.com

[ Upstream commit 89add40066f9ed9abe5f7f886fe5789ff7e0c50e ]

Tighten csum_start and csum_offset checks in virtio_net_hdr_to_skb for GSO packets.

The function already checks that a checksum requested with VIRTIO_NET_HDR_F_NEEDS_CSUM is in skb linear. But for GSO packets this might not hold for segs after segmentation.

Syzkaller demonstrated to reach this warning in skb_checksum_help

offset = skb_checksum_start_offset(skb); ret = -EINVAL; if (WARN_ON_ONCE(offset >= skb_headlen(skb)))

By injecting a TSO packet:

WARNING: CPU: 1 PID: 3539 at net/core/dev.c:3284 skb_checksum_help+0x3d0/0x5b0 ip_do_fragment+0x209/0x1b20 net/ipv4/ip_output.c:774 ip_finish_output_gso net/ipv4/ip_output.c:279 [inline] __ip_finish_output+0x2bd/0x4b0 net/ipv4/ip_output.c:301 iptunnel_xmit+0x50c/0x930 net/ipv4/ip_tunnel_core.c:82 ip_tunnel_xmit+0x2296/0x2c70 net/ipv4/ip_tunnel.c:813 __gre_xmit net/ipv4/ip_gre.c:469 [inline] ipgre_xmit+0x759/0xa60 net/ipv4/ip_gre.c:661 __netdev_start_xmit include/linux/netdevice.h:4850 [inline] netdev_start_xmit include/linux/netdevice.h:4864 [inline] xmit_one net/core/dev.c:3595 [inline] dev_hard_start_xmit+0x261/0x8c0 net/core/dev.c:3611 __dev_queue_xmit+0x1b97/0x3c90 net/core/dev.c:4261 packet_snd net/packet/af_packet.c:3073 [inline]

The geometry of the bad input packet at tcp_gso_segment:

[ 52.003050][ T8403] skb len=12202 headroom=244 headlen=12093 tailroom=0 [ 52.003050][ T8403] mac=(168,24) mac_len=24 net=(192,52) trans=244 [ 52.003050][ T8403] shinfo(txflags=0 nr_frags=1 gso(size=1552 type=3 segs=0)) [ 52.003050][ T8403] csum(0x60000c7 start=199 offset=1536 ip_summed=3 complete_sw=0 valid=0 level=0)

Mitigate with stricter input validation.

csum_offset: for GSO packets, deduce the correct value from gso_type. This is already done for USO. Extend it to TSO. Let UFO be: udp[46]_ufo_fragment ignores these fields and always computes the checksum in software.

csum_start: finding the real offset requires parsing to the transport header. Do not add a parser, use existing segmentation parsing. Thanks to SKB_GSO_DODGY, that also catches bad packets that are hw offloaded. Again test both TSO and USO. Do not test UFO for the above reason, and do not test UDP tunnel offload.

GSO packet are almost always CHECKSUM_PARTIAL. USO packets may be CHECKSUM_NONE since commit 10154db ("udp: Allow GSO transmit from devices with no checksum offload"), but then still these fields are initialized correctly in udp4_hwcsum/udp6_hwcsum_outgoing. So no need to test for ip_summed == CHECKSUM_PARTIAL first.

This revises an existing fix mentioned in the Fixes tag, which broke small packets with GSO offload, as detected by kselftests.

Link: https://syzkaller.appspot.com/bug?extid=e1db31216c789f552871 Link: https://lore.kernel.org/netdev/20240723223109.2196886-1-kuba@kernel.org Fixes: e269d79 ("net: missing check virtio") Cc: stable@vger.kernel.org Signed-off-by: Willem de Bruijn willemb@google.com Link: https://patch.msgid.link/20240729201108.1615114-1-willemdebruijn.kernel@gmai... Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Mathieu Tortuyaux mtortuyaux@microsoft.com --- Hi,

This patch fixes network failures on OpenStack VMs running with Kernel 5.15.165.

In 5.15.165, the commit "net: missing check virtio" is breaking networks on VMs that uses virtio in some conditions.

I slightly adapted the patch to have it fitting this branch (5.15.y).

Once patched and compiled it has been successfully tested on Flatcar CI with Kernel 5.15.165.

NOTE: This patch has already been backported on other stable branches (like 6.6.y)

Thanks,

Mathieu - @tormath1

include/linux/virtio_net.h | 17 ++++++----------- net/ipv4/tcp_offload.c | 3 +++ net/ipv4/udp_offload.c | 4 ++++ 3 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h index 29b19d0a324c..d9410d97158d 100644 --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -51,7 +51,6 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, unsigned int thlen = 0; unsigned int p_off = 0; unsigned int ip_proto; - u64 ret, remainder, gso_size;

if (hdr->gso_type != VIRTIO_NET_HDR_GSO_NONE) { switch (hdr->gso_type & ~VIRTIO_NET_HDR_GSO_ECN) { @@ -88,16 +87,6 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, u32 off = __virtio16_to_cpu(little_endian, hdr->csum_offset); u32 needed = start + max_t(u32, thlen, off + sizeof(__sum16));

- if (hdr->gso_size) { - gso_size = __virtio16_to_cpu(little_endian, hdr->gso_size); - ret = div64_u64_rem(skb->len, gso_size, &remainder); - if (!(ret && (hdr->gso_size > needed) && - ((remainder > needed) || (remainder == 0)))) { - return -EINVAL; - } - skb_shinfo(skb)->tx_flags |= SKBFL_SHARED_FRAG; - } - if (!pskb_may_pull(skb, needed)) return -EINVAL;

@@ -163,6 +152,12 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, if (gso_size == GSO_BY_FRAGS) return -EINVAL;

+ if ((gso_size & SKB_GSO_TCPV4) || + (gso_size & SKB_GSO_TCPV6)) { + if (skb->csum_offset != offsetof(struct tcphdr, check)) + return -EINVAL; + } + /* Too small packets are not really GSO ones. */ if (skb->len - nh_off > gso_size) { shinfo->gso_size = gso_size; diff --git a/net/ipv4/tcp_offload.c b/net/ipv4/tcp_offload.c index fc61cd3fea65..76684cbd63a4 100644 --- a/net/ipv4/tcp_offload.c +++ b/net/ipv4/tcp_offload.c @@ -71,6 +71,9 @@ struct sk_buff *tcp_gso_segment(struct sk_buff *skb, if (thlen < sizeof(*th)) goto out;

+ if (unlikely(skb_checksum_start(skb) != skb_transport_header(skb))) + goto out; + if (!pskb_may_pull(skb, thlen)) goto out;

diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c index c61268849948..61773a26fb34 100644 --- a/net/ipv4/udp_offload.c +++ b/net/ipv4/udp_offload.c @@ -279,6 +279,10 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb, if (gso_skb->len <= sizeof(*uh) + mss) return ERR_PTR(-EINVAL);

+ if (unlikely(skb_checksum_start(gso_skb) != + skb_transport_header(gso_skb))) + return ERR_PTR(-EINVAL); + skb_pull(gso_skb, sizeof(*uh));

/* clear destructor to avoid skb_segment assigning it to tail */