[PATCH 5.16 108/227] cfg80211: fix race in netlink owner interface destruction

Greg Kroah-Hartman
2022-02-21T09:58:44Z

From: Johannes Berg <johannes.berg@intel.com>

commit f0a6fd1527067da537e9c48390237488719948ed upstream.

My previous fix here to fix the deadlock left a race where
the exact same deadlock (see the original commit referenced
below) can still happen if cfg80211_destroy_ifaces() already
runs while nl80211_netlink_notify() is still marking some
interfaces as nl_owner_dead.

The race happens because we have two loops here - first we
dev_close() all the netdevs, and then we destroy them. If we
also have two netdevs (first one need only be a wdev though)
then we can find one during the first iteration, close it,
and go to the second iteration -- but then find two, and try
to destroy also the one we didn't close yet.

Fix this by only iterating once.

Reported-by: Toke Høiland-Jørgensen <toke@redhat.com>
Fixes: ea6b2098dd02 ("cfg80211: fix locking in netlink owner interface destruction")
Tested-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/r/20220201130951.22093-1-johannes@sipsolutions.net
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/wireless/core.c | 17 ++++-------------
1 file changed, 4 insertions(+), 13 deletions(-)

--- a/net/wireless/core.c
+++ b/net/wireless/core.c
@@ -5,7 +5,7 @@
* Copyright 2006-2010 Johannes Berg <johannes@sipsolutions.net>
* Copyright 2013-2014 Intel Mobile Communications GmbH
* Copyright 2015-2017 Intel Deutschland GmbH
- * Copyright (C) 2018-2021 Intel Corporation
+ * Copyright (C) 2018-2022 Intel Corporation
*/

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
@@ -332,29 +332,20 @@ static void cfg80211_event_work(struct w
void cfg80211_destroy_ifaces(struct cfg80211_registered_device *rdev)
{
struct wireless_dev *wdev, *tmp;
- bool found = false;

ASSERT_RTNL();

- list_for_each_entry(wdev, &rdev->wiphy.wdev_list, list) {
+ list_for_each_entry_safe(wdev, tmp, &rdev->wiphy.wdev_list, list) {
if (wdev->nl_owner_dead) {
if (wdev->netdev)
dev_close(wdev->netdev);
- found = true;
- }
- }
-
- if (!found)
- return;

- wiphy_lock(&rdev->wiphy);
- list_for_each_entry_safe(wdev, tmp, &rdev->wiphy.wdev_list, list) {
- if (wdev->nl_owner_dead) {
+ wiphy_lock(&rdev->wiphy);
cfg80211_leave(rdev, wdev);
rdev_del_virtual_intf(rdev, wdev);
+ wiphy_unlock(&rdev->wiphy);
}
}
- wiphy_unlock(&rdev->wiphy);
}

static void cfg80211_destroy_iface_wk(struct work_struct *work)