[B.A.T.M.A.N.] [PATCH maint 1/6] batman-adv: mcast: fix multicast tt/tvlv worker locking

Linus Lüssing linus.luessing at c0d3.blue
Wed Apr 24 03:19:14 CEST 2019


Syzbot has reported some issues with the locking assumptions made for
the multicast tt/tvlv worker: It was able to trigger the WARN_ON() in
batadv_mcast_mla_tt_retract() and batadv_mcast_mla_tt_add().
While hard/not reproduceable for us so far it seems that the
delayed_work_pending() we use might not be quite safe from reordering.

Therefore this patch adds an explicit, new spinlock to protect the
update of the mla_list and flags in bat_priv and then removes the
WARN_ON(delayed_work_pending()).

Reported-by: syzbot+83f2d54ec6b7e417e13f at syzkaller.appspotmail.com
Reported-by: syzbot+050927a651272b145a5d at syzkaller.appspotmail.com
Fixes: 40b384052672 ("batman-adv: Use own timer for multicast TT and TVLV updates")
Signed-off-by: Linus Lüssing <linus.luessing at c0d3.blue>
---
https://www.open-mesh.org/issues/369
https://www.open-mesh.org/issues/370

Remark: In the past, before 40b384052672, there things were actually explicitly
locked under the tt.commit_lock.
---
 net/batman-adv/main.c      |  1 +
 net/batman-adv/multicast.c | 11 +++--------
 net/batman-adv/types.h     |  5 +++++
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/batman-adv/main.c b/net/batman-adv/main.c
index dabcaff8..4a89177d 100644
--- a/net/batman-adv/main.c
+++ b/net/batman-adv/main.c
@@ -168,6 +168,7 @@ int batadv_mesh_init(struct net_device *soft_iface)
 	spin_lock_init(&bat_priv->tt.commit_lock);
 	spin_lock_init(&bat_priv->gw.list_lock);
 #ifdef CONFIG_BATMAN_ADV_MCAST
+	spin_lock_init(&bat_priv->mcast.mla_lock);
 	spin_lock_init(&bat_priv->mcast.want_lists_lock);
 #endif
 	spin_lock_init(&bat_priv->tvlv.container_list_lock);
diff --git a/net/batman-adv/multicast.c b/net/batman-adv/multicast.c
index 3feb9435..ec54e236 100644
--- a/net/batman-adv/multicast.c
+++ b/net/batman-adv/multicast.c
@@ -314,8 +314,6 @@ static void batadv_mcast_mla_list_free(struct hlist_head *mcast_list)
  * translation table except the ones listed in the given mcast_list.
  *
  * If mcast_list is NULL then all are retracted.
- *
- * Do not call outside of the mcast worker! (or cancel mcast worker first)
  */
 static void batadv_mcast_mla_tt_retract(struct batadv_priv *bat_priv,
 					struct hlist_head *mcast_list)
@@ -323,8 +321,6 @@ static void batadv_mcast_mla_tt_retract(struct batadv_priv *bat_priv,
 	struct batadv_hw_addr *mcast_entry;
 	struct hlist_node *tmp;
 
-	WARN_ON(delayed_work_pending(&bat_priv->mcast.work));
-
 	hlist_for_each_entry_safe(mcast_entry, tmp, &bat_priv->mcast.mla_list,
 				  list) {
 		if (mcast_list &&
@@ -348,8 +344,6 @@ static void batadv_mcast_mla_tt_retract(struct batadv_priv *bat_priv,
  *
  * Adds multicast listener announcements from the given mcast_list to the
  * translation table if they have not been added yet.
- *
- * Do not call outside of the mcast worker! (or cancel mcast worker first)
  */
 static void batadv_mcast_mla_tt_add(struct batadv_priv *bat_priv,
 				    struct hlist_head *mcast_list)
@@ -357,8 +351,6 @@ static void batadv_mcast_mla_tt_add(struct batadv_priv *bat_priv,
 	struct batadv_hw_addr *mcast_entry;
 	struct hlist_node *tmp;
 
-	WARN_ON(delayed_work_pending(&bat_priv->mcast.work));
-
 	if (!mcast_list)
 		return;
 
@@ -647,7 +639,10 @@ static void batadv_mcast_mla_update(struct work_struct *work)
 	priv_mcast = container_of(delayed_work, struct batadv_priv_mcast, work);
 	bat_priv = container_of(priv_mcast, struct batadv_priv, mcast);
 
+	spin_lock(&bat_priv->mcast.mla_lock);
 	__batadv_mcast_mla_update(bat_priv);
+	spin_unlock(&bat_priv->mcast.mla_lock);
+
 	batadv_mcast_start_timer(bat_priv);
 }
 
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 357ca119..74b64473 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -1211,6 +1211,11 @@ struct batadv_priv_mcast {
 	/** @bridged: whether the soft interface has a bridge on top */
 	unsigned char bridged:1;
 
+	/**
+	 * @mla_lock: a lock protecting mla_list and mla_flags
+	 */
+	spinlock_t mla_lock;
+
 	/**
 	 * @num_want_all_unsnoopables: number of nodes wanting unsnoopable IP
 	 *  traffic
-- 
2.20.1



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