CVE-2026-98950flow_dissector: avoid u16 truncation of hlen in bpf_flow_dissect()

Official description

In the Linux kernel, the following vulnerability has been resolved: flow_dissector: avoid u16 truncation of hlen in bpf_flow_dissect() bpf_flow_dissect() sanitizes the offsets returned by the BPF program with clamp_t(u16, ..., hlen). If hlen is bigger than 65535, the upper bound is truncated before the comparison. For instance, with hlen == 65536, both nhoff and thoff are forced to zero, even if the program returned sane values. This is the same class of bug as the one fixed in commit 99bda1ecbd56 ("flow_dissector: avoid u16 truncation of skb->len when computing thoff"). That fix does not cover the BPF path, because __skb_flow_dissect() returns early when a BPF flow dissector handles the packet. struct bpf_flow_keys stores nhoff and thoff as u16, so cap hlen to U16_MAX before clamping. Found by sashiko while reviewing the commit above.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/46d21495f633e38d40857401504ee51c56ffed2a
• https://git.kernel.org/stable/c/6267f8304cbd9ec9f3f53bd227a733e07131492e
• https://git.kernel.org/stable/c/99c59062172620a0bac4ae8cf37c83bb78772cdd
• https://git.kernel.org/stable/c/c44c02c930c6583b235a1937c69ff716c4bb4514
• https://git.kernel.org/stable/c/3fb5ad2951a6df92c98f4f06cd70f20c50a2eb2a
• https://git.kernel.org/stable/c/cc18eb0e9941162c03f03f411ed7f6c339d91fa0
• https://git.kernel.org/stable/c/61b43a51a55929ec040bee3ea51af2121b956d05
• https://git.kernel.org/stable/c/f202578efc738b883cfa04889eb97328914265a7