From: Willem de Bruijn <willemb@xxxxxxxxxx> commit 6513eb3d3191574b58859ef2d6dc26c0277c6f81 upstream. The referenced commit drops bad input, but has false positives. Tighten the check to avoid these. The check detects illegal checksum offload requests, which produce csum_start/csum_off beyond end of packet after segmentation. But it is based on two incorrect assumptions: 1. virtio_net_hdr_to_skb with VIRTIO_NET_HDR_GSO_TCP[46] implies GSO. True in callers that inject into the tx path, such as tap. But false in callers that inject into rx, like virtio-net. Here, the flags indicate GRO, and CHECKSUM_UNNECESSARY or CHECKSUM_NONE without VIRTIO_NET_HDR_F_NEEDS_CSUM is normal. 2. TSO requires checksum offload, i.e., ip_summed == CHECKSUM_PARTIAL. False, as tcp[46]_gso_segment will fix up csum_start and offset for all other ip_summed by calling __tcp_v4_send_check. Because of 2, we can limit the scope of the fix to virtio_net_hdr that do try to set these fields, with a bogus value. Link: https://lore.kernel.org/netdev/20240909094527.GA3048202@xxxxxxxxxx/ Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr") Signed-off-by: Willem de Bruijn <willemb@xxxxxxxxxx> Acked-by: Jason Wang <jasowang@xxxxxxxxxx> Acked-by: Michael S. Tsirkin <mst@xxxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://patch.msgid.link/20240910213553.839926-1-willemdebruijn.kernel@xxxxxxxxx Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- include/linux/virtio_net.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/include/linux/virtio_net.h +++ b/include/linux/virtio_net.h @@ -161,7 +161,8 @@ retry: break; case SKB_GSO_TCPV4: case SKB_GSO_TCPV6: - if (skb->csum_offset != offsetof(struct tcphdr, check)) + if (skb->ip_summed == CHECKSUM_PARTIAL && + skb->csum_offset != offsetof(struct tcphdr, check)) return -EINVAL; break; } Patches currently in stable-queue which might be from willemb@xxxxxxxxxx are queue-5.15/net-tighten-bad-gso-csum-offset-check-in-virtio_net_hdr.patch
