Patch "mac80211: fix locking in update_vlan_tailroom_need_count()" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    mac80211: fix locking in update_vlan_tailroom_need_count()

to the 4.1-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     mac80211-fix-locking-in-update_vlan_tailroom_need_count.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Fri Jul  3 20:00:25 PDT 2015
From: Johannes Berg <johannes.berg@intel.com>
Date: Wed, 17 Jun 2015 13:54:54 +0200
Subject: mac80211: fix locking in update_vlan_tailroom_need_count()

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

[ Upstream commit 51f458d9612177f69c2e2c437034ae15f93078e7 ]

Unfortunately, Michal's change to fix AP_VLAN crypto tailroom
caused a locking issue that was reported by lockdep, but only
in a few cases - the issue was a classic ABBA deadlock caused
by taking the mtx after the key_mtx, where normally they're
taken the other way around.

As the key mutex protects the field in question (I'm adding a
few annotations to make that clear) only the iteration needs
to be protected, but we can also iterate the interface list
with just RCU protection while holding the key mutex.

Fixes: f9dca80b98ca ("mac80211: fix AP_VLAN crypto tailroom calculation")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/mac80211/key.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/net/mac80211/key.c
+++ b/net/mac80211/key.c
@@ -66,12 +66,15 @@ update_vlan_tailroom_need_count(struct i
 	if (sdata->vif.type != NL80211_IFTYPE_AP)
 		return;
 
-	mutex_lock(&sdata->local->mtx);
+	/* crypto_tx_tailroom_needed_cnt is protected by this */
+	assert_key_lock(sdata->local);
 
-	list_for_each_entry(vlan, &sdata->u.ap.vlans, u.vlan.list)
+	rcu_read_lock();
+
+	list_for_each_entry_rcu(vlan, &sdata->u.ap.vlans, u.vlan.list)
 		vlan->crypto_tx_tailroom_needed_cnt += delta;
 
-	mutex_unlock(&sdata->local->mtx);
+	rcu_read_unlock();
 }
 
 static void increment_tailroom_need_count(struct ieee80211_sub_if_data *sdata)
@@ -95,6 +98,8 @@ static void increment_tailroom_need_coun
 	 * http://mid.gmane.org/1308590980.4322.19.camel@jlt3.sipsolutions.net
 	 */
 
+	assert_key_lock(sdata->local);
+
 	update_vlan_tailroom_need_count(sdata, 1);
 
 	if (!sdata->crypto_tx_tailroom_needed_cnt++) {
@@ -109,6 +114,8 @@ static void increment_tailroom_need_coun
 static void decrease_tailroom_need_count(struct ieee80211_sub_if_data *sdata,
 					 int delta)
 {
+	assert_key_lock(sdata->local);
+
 	WARN_ON_ONCE(sdata->crypto_tx_tailroom_needed_cnt < delta);
 
 	update_vlan_tailroom_need_count(sdata, -delta);


Patches currently in stable-queue which might be from johannes.berg@intel.com are

queue-4.1/mac80211-fix-locking-in-update_vlan_tailroom_need_count.patch