mac80211 copies cfg80211's variable-length countdown offset list into a zero-initialized fixed-size array, leaving unused entries at zero. The beacon branch already skips those zero entries, but the AP probe-response branch writes through them unconditionally. When a probe-response template has no countdown offset, the write through an unused zero entry overwrites resp->data[0], corrupting the first byte of the template. cfg80211 already bounds explicitly supplied non-zero offsets in nl80211_parse_counter_offsets(), so this is a zero-sentinel bug, not an out-of-bounds write. Skip zero probe-response offsets, matching the beacon path. Fixes: af296bdb8da4 ("mac80211: move csa counters from sdata to beacon/presp") Link: https://lore.kernel.org/all/20260708195911.84365-6-enderaoelyther@gmail.com/ Assisted-by: Codex:gpt-5 Assisted-by: Claude:opus-4.8 Signed-off-by: Zhao Li --- Changes in v2: - Describe offset zero as the unused-entry sentinel; do not claim an out-of-bounds access. net/mac80211/tx.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c index 91b14112e24f0..fd4c379b3f201 100644 --- a/net/mac80211/tx.c +++ b/net/mac80211/tx.c @@ -5249,7 +5249,8 @@ static void ieee80211_set_beacon_cntdwn(struct ieee80211_sub_if_data *sdata, if (sdata->vif.type == NL80211_IFTYPE_AP && resp) { u16 *resp_offsets = resp->cntdwn_counter_offsets; - resp->data[resp_offsets[i]] = count; + if (resp_offsets[i]) + resp->data[resp_offsets[i]] = count; } } } -- 2.50.1 (Apple Git-155)