6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Eric Dumazet [ Upstream commit f202578efc738b883cfa04889eb97328914265a7 ] 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. Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook") Signed-off-by: Eric Dumazet Link: https://patch.msgid.link/20261007045616.445596-1-edumazet@kernel.org Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/core/flow_dissector.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c index 37864578e8687..57fb95186238a 100644 --- a/net/core/flow_dissector.c +++ b/net/core/flow_dissector.c @@ -999,6 +999,8 @@ u32 bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx, result = bpf_prog_run_pin_on_cpu(prog, ctx); + /* bpf_flow_keys offsets are u16: do not let @hlen be truncated. */ + hlen = min_t(int, hlen, U16_MAX); flow_keys->nhoff = clamp_t(u16, flow_keys->nhoff, nhoff, hlen); flow_keys->thoff = clamp_t(u16, flow_keys->thoff, flow_keys->nhoff, hlen); -- 2.53.0