batman-adv: Make DAT capability changes atomic

commit 65d7d460 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: 17cf0ea4 ("batman-adv: tvlv - add distributed arp table container")
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>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

net/batman-adv/distributed-arp-table.c

@@ -17,6 +17,7 @@
  * 02110-1301, USA
  */
 
+#include <linux/bitops.h>
 #include <linux/if_ether.h>
 #include <linux/if_arp.h>
 #include <linux/if_vlan.h>
@@ -424,7 +425,7 @@ static bool batadv_is_orig_node_eligible(struct batadv_dat_candidate *res,
 	int j;
 
 	/* check if orig node candidate is running DAT */
-	if (!(candidate->capabilities & BATADV_ORIG_CAPA_HAS_DAT))
+	if (!test_bit(BATADV_ORIG_CAPA_HAS_DAT, &candidate->capabilities))
 		goto out;
 
 	/* Check if this node has already been selected... */
@@ -681,9 +682,9 @@ static void batadv_dat_tvlv_ogm_handler_v1(struct batadv_priv *bat_priv,
 					   uint16_t tvlv_value_len)
 {
 	if (flags & BATADV_TVLV_HANDLER_OGM_CIFNOTFND)
-		orig->capabilities &= ~BATADV_ORIG_CAPA_HAS_DAT;
+		clear_bit(BATADV_ORIG_CAPA_HAS_DAT, &orig->capabilities);
 	else
-		orig->capabilities |= BATADV_ORIG_CAPA_HAS_DAT;
+		set_bit(BATADV_ORIG_CAPA_HAS_DAT, &orig->capabilities);
 }
 
 /**

net/batman-adv/types.h

@@ -217,7 +217,7 @@ struct batadv_orig_node {
 	unsigned long last_seen;
 	unsigned long bcast_seqno_reset;
 	unsigned long batman_seqno_reset;
-	uint8_t capabilities;
+	unsigned long capabilities;
 	atomic_t last_ttvn;
 	unsigned char *tt_buff;
 	int16_t tt_buff_len;
@@ -258,7 +258,7 @@ struct batadv_orig_node {
  * @BATADV_ORIG_CAPA_HAS_NC: orig node has network coding enabled
  */
 enum batadv_orig_capabilities {
-	BATADV_ORIG_CAPA_HAS_DAT = BIT(0),
+	BATADV_ORIG_CAPA_HAS_DAT,
 	BATADV_ORIG_CAPA_HAS_NC = BIT(1),
 };