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[80.71.142.18]) by smtp.gmail.com with ESMTPSA id o20-20020a170906769400b0077a11b79b9bsm24901ejm.133.2022.12.09.07.28.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Dec 2022 07:28:49 -0800 (PST) From: =?UTF-8?q?Alvin=20=C5=A0ipraga?= To: Johannes Berg , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: =?UTF-8?q?Alvin=20=C5=A0ipraga?= , linux-wireless@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH next] wifi: nl80211: emit CMD_START_AP on multicast group when an AP is started Date: Fri, 9 Dec 2022 16:28:36 +0100 Message-Id: <20221209152836.1667196-1-alvin@pqrs.dk> X-Mailer: git-send-email 2.37.3 MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Alvin =C5=A0ipraga Userspace processes such as network daemons may wish to be informed when any AP interface is brought up on the system, for example to initiate a (re)configuration of IP settings or to start a DHCP server. Currently nl80211 does not broadcast any such event on its multicast groups, leaving userspace only two options: 1. the process must be the one that actually issued the NL80211_CMD_START_AP request, so that it can react on the response to that request; 2. the process must react to RTM_NEWLINK events indicating a change in carrier state, and may query for further information about the AP and react accordingly. Option (1) is robust, but it does not cover all scenarios. It is easy to imagine a situation where this is not the case (e.g. hostapd + systemd-networkd). Option (2) is not robust, because RTM_NEWLINK events may be silently discarded by the linkwatch logic (cf. linkwatch_fire_event()). Concretely, consider a scenario in which the carrier state flip-flops in the following way: ^ carrier state (high/low =3D carrier/no carrier) | | _______ _______ ... | | | | | ______| "foo" |____| "bar" (SSID in "quotes") | +-------A-------B----C---------> time If the time interval between (A) and (C) is less than 1 second, then linkwatch may emit only a single RTM_NEWLINK event indicating carrier gain. This is problematic because it is possible that the network configuration that should be applied is a function of the AP's properties such as SSID (cf. SSID=3D in systemd.network(5)). As illustrated in the above diagram, it may be that the AP with SSID "bar" ends up being configured as though it had SSID "foo". Address the above issue by having nl80211 emit an NL80211_CMD_START_AP message on the MLME nl80211 multicast group. This allows for arbitrary processes to be reliably informed. Signed-off-by: Alvin =C5=A0ipraga --- net/wireless/nl80211.c | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c index 33a82ecab9d5..323b7e40d855 100644 --- a/net/wireless/nl80211.c +++ b/net/wireless/nl80211.c @@ -5770,6 +5770,39 @@ static bool nl80211_valid_auth_type(struct cfg80211_= registered_device *rdev, } } =20 +static void nl80211_send_ap_started(struct wireless_dev *wdev) +{ + struct wiphy *wiphy =3D wdev->wiphy; + struct cfg80211_registered_device *rdev =3D wiphy_to_rdev(wiphy); + struct sk_buff *msg; + void *hdr; + + msg =3D nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL); + if (!msg) + return; + + hdr =3D nl80211hdr_put(msg, 0, 0, 0, NL80211_CMD_START_AP); + if (!hdr) + goto out; + + if (nla_put_u32(msg, NL80211_ATTR_WIPHY, rdev->wiphy_idx) || + nla_put_u32(msg, NL80211_ATTR_IFINDEX, wdev->netdev->ifindex) || + nla_put_u64_64bit(msg, NL80211_ATTR_WDEV, wdev_id(wdev), + NL80211_ATTR_PAD) || + (wdev->u.ap.ssid_len && + nla_put(msg, NL80211_ATTR_SSID, wdev->u.ap.ssid_len, + wdev->u.ap.ssid))) + goto out; + + genlmsg_end(msg, hdr); + + genlmsg_multicast_netns(&nl80211_fam, wiphy_net(wiphy), msg, 0, + NL80211_MCGRP_MLME, GFP_KERNEL); + return; +out: + nlmsg_free(msg); +} + static int nl80211_start_ap(struct sk_buff *skb, struct genl_info *info) { struct cfg80211_registered_device *rdev =3D info->user_ptr[0]; @@ -6050,6 +6083,8 @@ static int nl80211_start_ap(struct sk_buff *skb, stru= ct genl_info *info) =20 if (info->attrs[NL80211_ATTR_SOCKET_OWNER]) wdev->conn_owner_nlportid =3D info->snd_portid; + + nl80211_send_ap_started(wdev); } out_unlock: wdev_unlock(wdev); --=20 2.37.3