From: Weiming Yang ieee80211_start_ap() enters the EHT block when params->eht_cap is set, but its last statement unconditionally dereferences params->eht_oper. The two pointers are parsed from separate beacon-tail elements in nl80211_calculate_ap_params(), and an EHT Operation element is not required to be present when an EHT Capability element is. A beacon tail carrying an HE Capability and HE Operation element (so he_support is set) plus an EHT Capability element, but no EHT Operation element, thus dereferences a NULL params->eht_oper: KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: 0010:ieee80211_start_ap (net/mac80211/cfg.c:1599) Call Trace: nl80211_start_ap (net/wireless/nl80211.c:7177) genl_family_rcv_msg_doit (net/netlink/genetlink.c:1114) genl_rcv_msg (net/netlink/genetlink.c:1209) netlink_rcv_skb (net/netlink/af_netlink.c:2550) genl_rcv (net/netlink/genetlink.c:1218) netlink_unicast (net/netlink/af_netlink.c:1344) netlink_sendmsg (net/netlink/af_netlink.c:1894) __sys_sendto (net/socket.c:2265) NL80211_CMD_START_AP uses GENL_UNS_ADMIN_PERM, so this is reachable by an unprivileged user in a user namespace. Guard the dereference on params->eht_oper, as the HE block above already does for params->he_oper. Fixes: 22c64f37e1d4 ("wifi: mac80211: Update MCS15 support in link_conf") Reported-by: Xiang Mei Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Weiming Shi --- net/mac80211/cfg.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/net/mac80211/cfg.c b/net/mac80211/cfg.c index 7b77d57c9f96f..5e8d4ccaa6be4 100644 --- a/net/mac80211/cfg.c +++ b/net/mac80211/cfg.c @@ -1595,9 +1595,10 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev, (IEEE80211_EHT_PHY_CAP7_NON_OFDMA_UL_MU_MIMO_80MHZ | IEEE80211_EHT_PHY_CAP7_NON_OFDMA_UL_MU_MIMO_160MHZ | IEEE80211_EHT_PHY_CAP7_NON_OFDMA_UL_MU_MIMO_320MHZ); - link_conf->eht_disable_mcs15 = - u8_get_bits(params->eht_oper->params, - IEEE80211_EHT_OPER_MCS15_DISABLE); + if (params->eht_oper) + link_conf->eht_disable_mcs15 = + u8_get_bits(params->eht_oper->params, + IEEE80211_EHT_OPER_MCS15_DISABLE); } else { link_conf->eht_su_beamformer = false; link_conf->eht_su_beamformee = false; -- 2.43.0