batman-adv: Make MCAST capability changes atomic

commit 9c936e3f upstream.

Bitwise OR/AND assignments in C aren't guaranteed to be atomic. One
OGM handler might undo the set/clear of a specific bit from another
handler run in between.

Fix this by using the atomic set_bit()/clear_bit()/test_bit() functions.

Fixes: 60432d75 ("batman-adv: Announce new capability via multicast TVLV")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: Antonio Quartulli <antonio@meshcoding.com>
[ luis: backported to 3.16: adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

net/batman-adv/multicast.c

@@ -22,6 +22,8 @@
 #include "translation-table.h"
 #include "multicast.h"
 
+#include <linux/bitops.h>
+
 /**
  * batadv_mcast_mla_softif_get - get softif multicast listeners
  * @dev: the device to collect multicast addresses from
@@ -675,29 +677,30 @@ static void batadv_mcast_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
 	uint8_t mcast_flags = BATADV_NO_FLAGS;
 	bool orig_initialized;
 
-	orig_initialized = orig->capa_initialized & BATADV_ORIG_CAPA_HAS_MCAST;
+	orig_initialized = test_bit(BATADV_ORIG_CAPA_HAS_MCAST,
+				    &orig->capa_initialized);
 
 	/* If mcast support is turned on decrease the disabled mcast node
 	 * counter only if we had increased it for this node before. If this
 	 * is a completely new orig_node no need to decrease the counter.
 	 */
 	if (orig_mcast_enabled &&
-	    !(orig->capabilities & BATADV_ORIG_CAPA_HAS_MCAST)) {
+	    !test_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capabilities)) {
 		if (orig_initialized)
 			atomic_dec(&bat_priv->mcast.num_disabled);
-		orig->capabilities |= BATADV_ORIG_CAPA_HAS_MCAST;
+		set_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capabilities);
 	/* If mcast support is being switched off or if this is an initial
 	 * OGM without mcast support then increase the disabled mcast
 	 * node counter.
 	 */
 	} else if (!orig_mcast_enabled &&
-		   (orig->capabilities & BATADV_ORIG_CAPA_HAS_MCAST ||
+		   (test_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capabilities) ||
 		    !orig_initialized)) {
 		atomic_inc(&bat_priv->mcast.num_disabled);
-		orig->capabilities &= ~BATADV_ORIG_CAPA_HAS_MCAST;
+		clear_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capabilities);
 	}
 
-	orig->capa_initialized |= BATADV_ORIG_CAPA_HAS_MCAST;
+	set_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capa_initialized);
 
 	if (orig_mcast_enabled && tvlv_value &&
 	    (tvlv_value_len >= sizeof(mcast_flags)))
@@ -741,8 +744,8 @@ void batadv_mcast_purge_orig(struct batadv_orig_node *orig)
 {
 	struct batadv_priv *bat_priv = orig->bat_priv;
 
-	if (!(orig->capabilities & BATADV_ORIG_CAPA_HAS_MCAST) &&
-	    orig->capa_initialized & BATADV_ORIG_CAPA_HAS_MCAST)
+	if (!test_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capabilities) &&
+	    test_bit(BATADV_ORIG_CAPA_HAS_MCAST, &orig->capa_initialized))
 		atomic_dec(&bat_priv->mcast.num_disabled);
 
 	batadv_mcast_want_unsnoop_update(bat_priv, orig, BATADV_NO_FLAGS);

net/batman-adv/types.h

@@ -301,7 +301,7 @@ enum batadv_orig_capabilities {
 	BATADV_ORIG_CAPA_HAS_DAT,
 	BATADV_ORIG_CAPA_HAS_NC,
 	BATADV_ORIG_CAPA_HAS_TT,
-	BATADV_ORIG_CAPA_HAS_MCAST = BIT(3),
+	BATADV_ORIG_CAPA_HAS_MCAST,
 };
 
 /**