linux-kernel - Re: [PATCH next] wifi: nl80211: emit CMD_START_AP on multicast group when an AP is started

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Message-ID: <c7eac35785bf672b3b9da45c41baa4149a632daa.camel@sipsolutions.net>
Date:   Wed, 18 Jan 2023 17:26:19 +0100
From:   Johannes Berg <johannes@...solutions.net>
To:     Alvin Šipraga <alvin@...s.dk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     Alvin Šipraga <alsi@...g-olufsen.dk>,
        linux-wireless@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH next] wifi: nl80211: emit CMD_START_AP on multicast
 group when an AP is started

On Fri, 2022-12-09 at 16:28 +0100, Alvin Šipraga wrote:
> 
> 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= 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".
> 

You might not care if you want the SSID, but it still seems wrong:

> +static void nl80211_send_ap_started(struct wireless_dev *wdev)
> +{
> +	struct wiphy *wiphy = wdev->wiphy;
> +	struct cfg80211_registered_device *rdev = wiphy_to_rdev(wiphy);
> +	struct sk_buff *msg;
> +	void *hdr;
> +
> +	msg = nlmsg_new(NLMSG_DEFAULT_SIZE, GFP_KERNEL);
> +	if (!msg)
> +		return;
> +
> +	hdr = 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);
> +}

This has no indication of the link, but with multi-link you could
actually be sending this event multiple times to userspace on the same
netdev.

>  static int nl80211_start_ap(struct sk_buff *skb, struct genl_info *info)
>  {
>  	struct cfg80211_registered_device *rdev = info->user_ptr[0];
> @@ -6050,6 +6083,8 @@ static int nl80211_start_ap(struct sk_buff *skb, struct genl_info *info)
>  
>  		if (info->attrs[NL80211_ATTR_SOCKET_OWNER])
>  			wdev->conn_owner_nlportid = info->snd_portid;
> +
> +		nl80211_send_ap_started(wdev);
>  	}

because this can be called multiple times, once for each link.

Seems like you should include the link ID or something?

johannes