[PATCH wireless-next 07/28] wifi: mac80211: Fix use-after-free of debugfs inodes.

[greearb@candelatech.com]

From: Ben Greear <greearb@candelatech.com>

When recursively removing debugfs files, clean up child link
debugfs pointers since the recursive removal will have deleted
their memory.  This fixes use-after-free problem when those child
links are eventually cleaned up.

Signed-off-by: Ben Greear <greearb@candelatech.com>
---
 net/mac80211/debugfs_netdev.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/net/mac80211/debugfs_netdev.c b/net/mac80211/debugfs_netdev.c
index 51d2ae232a85..bc2da35db4ae 100644
--- a/net/mac80211/debugfs_netdev.c
+++ b/net/mac80211/debugfs_netdev.c
@@ -1039,9 +1039,28 @@ static void ieee80211_debugfs_add_netdev(struct ieee80211_sub_if_data *sdata,
 
 void ieee80211_debugfs_remove_netdev(struct ieee80211_sub_if_data *sdata)
 {
+	struct ieee80211_link_data *link;
+	int i;
+
 	if (!sdata->vif.debugfs_dir)
 		return;
 
+	/* In case where there were errors on station creation and maybe
+	 * teardown, we may get here with some links still active.  We are
+	 * about to recursively delete debugfs, so remove any pointers the
+	 * links may have.
+	 */
+	rcu_read_lock();
+
+	for (i = 0; i < IEEE80211_MLD_MAX_NUM_LINKS; i++) {
+		link = rcu_access_pointer(sdata->link[i]);
+		if (!link)
+			continue;
+
+		link->debugfs_dir = NULL;
+	}
+	rcu_read_unlock();
+
 	debugfs_remove_recursive(sdata->vif.debugfs_dir);
 	sdata->vif.debugfs_dir = NULL;
 	sdata->debugfs.subdir_stations = NULL;
-- 
2.42.0