CVE-2025-68725

In the Linux kernel, the following vulnerability has been resolved:

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 121d57af308d ("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.