cfg80211: allow userspace to take ownership of interfaces

When dynamically creating interfaces from userspace, e.g. for P2P usage,
such interfaces are usually owned by the process that created them, i.e.
wpa_supplicant. Should wpa_supplicant crash, such interfaces will often
cease operating properly and cause problems on restarting the process.

To avoid this problem, introduce an ownership concept for interfaces. If
an interface is owned by a netlink socket, then it will be destroyed if
the netlink socket is closed for any reason, including if the process it
belongs to crashed. This gives us a race-free way to get rid of any such
interfaces.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 27 insertions, 1 deletions

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 052c1bf..b25b5ce 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -385,6 +385,7 @@ static const struct nla_policy nl80211_policy[NL80211_ATTR_MAX+1] = {
 	[NL80211_ATTR_MAC_HINT] = { .len = ETH_ALEN },
 	[NL80211_ATTR_WIPHY_FREQ_HINT] = { .type = NLA_U32 },
 	[NL80211_ATTR_TDLS_PEER_CAPABILITY] = { .type = NLA_U32 },
+	[NL80211_ATTR_IFACE_SOCKET_OWNER] = { .type = NLA_FLAG },
 };
 
 /* policy for the key attributes */
@@ -2514,6 +2515,9 @@ static int nl80211_new_interface(struct sk_buff *skb, struct genl_info *info)
 	enum nl80211_iftype type = NL80211_IFTYPE_UNSPECIFIED;
 	u32 flags;
 
+	/* to avoid failing a new interface creation due to pending removal */
+	cfg80211_destroy_ifaces(rdev);
+
 	memset(&params, 0, sizeof(params));
 
 	if (!info->attrs[NL80211_ATTR_IFNAME])
@@ -2563,6 +2567,9 @@ static int nl80211_new_interface(struct sk_buff *skb, struct genl_info *info)
 		return PTR_ERR(wdev);
 	}
 
+	if (info->attrs[NL80211_ATTR_IFACE_SOCKET_OWNER])
+		wdev->owner_nlportid = info->snd_portid;
+
 	switch (type) {
 	case NL80211_IFTYPE_MESH_POINT:
 		if (!info->attrs[NL80211_ATTR_MESH_ID])
@@ -11649,9 +11656,15 @@ static int nl80211_netlink_notify(struct notifier_block * nb,
 	rcu_read_lock();
 
 	list_for_each_entry_rcu(rdev, &cfg80211_rdev_list, list) {
-		list_for_each_entry_rcu(wdev, &rdev->wdev_list, list)
+		bool schedule_destroy_work = false;
+
+		list_for_each_entry_rcu(wdev, &rdev->wdev_list, list) {
 			cfg80211_mlme_unregister_socket(wdev, notify->portid);
 
+			if (wdev->owner_nlportid == notify->portid)
+				schedule_destroy_work = true;
+		}
+
 		spin_lock_bh(&rdev->beacon_registrations_lock);
 		list_for_each_entry_safe(reg, tmp, &rdev->beacon_registrations,
 					 list) {
@@ -11662,6 +11675,19 @@ static int nl80211_netlink_notify(struct notifier_block * nb,
 			}
 		}
 		spin_unlock_bh(&rdev->beacon_registrations_lock);
+
+		if (schedule_destroy_work) {
+			struct cfg80211_iface_destroy *destroy;
+
+			destroy = kzalloc(sizeof(*destroy), GFP_ATOMIC);
+			if (destroy) {
+				destroy->nlportid = notify->portid;
+				spin_lock(&rdev->destroy_list_lock);
+				list_add(&destroy->list, &rdev->destroy_list);
+				spin_unlock(&rdev->destroy_list_lock);
+				schedule_work(&rdev->destroy_work);
+			}
+		}
 	}
 
 	rcu_read_unlock();