batman-adv: Fix potential broadcast BLA-duplicate-check race condition

Threads in the bottom half of batadv_bla_check_bcast_duplist() might
otherwise for instance overwrite variables which other threads might
be using/reading at the same time in the top half, potentially
leading to messing up the bcast_duplist, possibly resulting in false
bridge loop avoidance duplicate check decisions.

Signed-off-by: Linus Lüssing <linus.luessing@web.de>
Acked-by: Simon Wunderlich <siwu@hrz.tu-chemnitz.de>
Signed-off-by: Marek Lindner <lindner_marek@yahoo.de>

2 files changed, 16 insertions, 5 deletions

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index eebab20c7478..fd8d5afec0dd 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -1167,6 +1167,8 @@ int batadv_bla_init(struct batadv_priv *bat_priv)
         uint16_t crc;
         unsigned long entrytime;
 
+        spin_lock_init(&bat_priv->bla.bcast_duplist_lock);
+
         batadv_dbg(BATADV_DBG_BLA, bat_priv, "bla hash registering\n");
 
         /* setting claim destination address */
@@ -1226,7 +1228,7 @@ int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
                                    struct batadv_bcast_packet *bcast_packet,
                                    int bcast_packet_len)
 {
-        int i, length, curr;
+        int i, length, curr, ret = 0;
         uint8_t *content;
         uint16_t crc;
         struct batadv_bcast_duplist_entry *entry;
@@ -1238,6 +1240,8 @@ int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
         /* calculate the crc ... */
         crc = crc16(0, content, length);
 
+        spin_lock_bh(&bat_priv->bla.bcast_duplist_lock);
+
         for (i = 0; i < BATADV_DUPLIST_SIZE; i++) {
                 curr = (bat_priv->bla.bcast_duplist_curr + i);
                 curr %= BATADV_DUPLIST_SIZE;
@@ -1259,9 +1263,12 @@ int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
                 /* this entry seems to match: same crc, not too old,
                  * and from another gw. therefore return 1 to forbid it.
                  */
-                return 1;
+                ret = 1;
+                goto out;
         }
-        /* not found, add a new entry (overwrite the oldest entry) */
+        /* not found, add a new entry (overwrite the oldest entry)
+         * and allow it, its the first occurence.
+         */
         curr = (bat_priv->bla.bcast_duplist_curr + BATADV_DUPLIST_SIZE - 1);
         curr %= BATADV_DUPLIST_SIZE;
         entry = &bat_priv->bla.bcast_duplist[curr];
@@ -1270,8 +1277,10 @@ int batadv_bla_check_bcast_duplist(struct batadv_priv *bat_priv,
         memcpy(entry->orig, bcast_packet->orig, ETH_ALEN);
         bat_priv->bla.bcast_duplist_curr = curr;
 
-        /* allow it, its the first occurence. */
-        return 0;
+out:
+        spin_unlock_bh(&bat_priv->bla.bcast_duplist_lock);
+
+        return ret;
 }
 
 
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index 2ed82caacdca..ac1e07a80454 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -205,6 +205,8 @@ struct batadv_priv_bla {
         struct batadv_hashtable *backbone_hash;
         struct batadv_bcast_duplist_entry bcast_duplist[BATADV_DUPLIST_SIZE];
         int bcast_duplist_curr;
+        /* protects bcast_duplist and bcast_duplist_curr */
+        spinlock_t bcast_duplist_lock;
         struct batadv_bla_claim_dst claim_dest;
         struct delayed_work work;
 };