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net: tighten bad gso csum offset check in virtio_net_hdr
stable inclusion from stable-v6.6.52 commit 4ec0d8dbd7025d0dd0e00ac8a4e0df3d02045e97 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/IAYXOD Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4ec0d8dbd7025d0dd0e00ac8a4e0df3d02045e97 -------------------------------- 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@port70.net/ Fixes: 89add40066f9 ("net: drop bad gso csum_start and offset in virtio_net_hdr") Signed-off-by:Willem de Bruijn <willemb@google.com> Acked-by: