Daniel Borkmann 04a899573f bpf: Do not let BPF test infra emit invalid GSO types to stack ... Yinhao et al. reported that their fuzzer tool was able to trigger a skb_warn_bad_offload() from netif_skb_features() -> gso_features_check(). When a BPF program - triggered via BPF test infra - pushes the packet to the loopback device via bpf_clone_redirect() then mentioned offload warning can be seen. GSO-related features are then rightfully disabled. We get into this situation due to convert___skb_to_skb() setting gso_segs and gso_size but not gso_type. Technically, it makes sense that this warning triggers since the GSO properties are malformed due to the gso_type. Potentially, the gso_type could be marked non-trustworthy through setting it at least to SKB_GSO_DODGY without any other specific assumptions, but that also feels wrong given we should not go further into the GSO engine in the first place. The checks were added in 121d57af30 ("gso: validate gso_type in GSO handlers") because there were malicious (syzbot) senders that combine a protocol with a non-matching gso_type. If we would want to drop such packets, gso_features_check() currently only returns feature flags via netif_skb_features(), so one location for potentially dropping such skbs could be validate_xmit_unreadable_skb(), but then otoh it would be an additional check in the fast-path for a very corner case. Given bpf_clone_redirect() is the only place where BPF test infra could emit such packets, lets reject them right there. Fixes: 850a88cc40 ("bpf: Expose __sk_buff wire_len/gso_segs to BPF_PROG_TEST_RUN") Fixes: cf62089b0e ("bpf: Add gso_size to __sk_buff") Reported-by: Yinhao Hu <dddddd@hust.edu.cn> Reported-by: Kaiyan Mei <M202472210@hust.edu.cn> Reported-by: Dongliang Mu <dzm91@hust.edu.cn> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org> Link: https://patch.msgid.link/20251020075441.127980-1-daniel@iogearbox.net		2025-10-20 13:16:10 -07:00
..
Makefile	bpf: Add dummy BPF STRUCT_OPS for test purpose	2021-11-01 14:10:00 -07:00
bpf_dummy_struct_ops.c	bpf: Add attach_type field to bpf_link	2025-07-11 10:51:55 -07:00
test_run.c	bpf: Do not let BPF test infra emit invalid GSO types to stack	2025-10-20 13:16:10 -07:00