[linux-next] LinuxNextTracking branch, master, updated. next-20190329

batman at open-mesh.org batman at open-mesh.org
Sat Mar 30 00:19:29 CET 2019

The following commit has been merged in the master branch:
commit 4ba104f468bbfc27362c393815d03aa18fb7a20f
Author: Sven Eckelmann <sven at narfation.org>
Date:   Sat Feb 23 14:27:10 2019 +0100

    batman-adv: Reduce claim hash refcnt only for removed entry
    The batadv_hash_remove is a function which searches the hashtable for an
    entry using a needle, a hashtable bucket selection function and a compare
    function. It will lock the bucket list and delete an entry when the compare
    function matches it with the needle. It returns the pointer to the
    hlist_node which matches or NULL when no entry matches the needle.
    The batadv_bla_del_claim is not itself protected in anyway to avoid that
    any other function is modifying the hashtable between the search for the
    entry and the call to batadv_hash_remove. It can therefore happen that the
    entry either doesn't exist anymore or an entry was deleted which is not the
    same object as the needle. In such an situation, the reference counter (for
    the reference stored in the hashtable) must not be reduced for the needle.
    Instead the reference counter of the actually removed entry has to be
    Otherwise the reference counter will underflow and the object might be
    freed before all its references were dropped. The kref helpers reported
    this problem as:
      refcount_t: underflow; use-after-free.
    Fixes: 23721387c409 ("batman-adv: add basic bridge loop avoidance code")
    Signed-off-by: Sven Eckelmann <sven at narfation.org>
    Signed-off-by: Simon Wunderlich <sw at simonwunderlich.de>

diff --git a/net/batman-adv/bridge_loop_avoidance.c b/net/batman-adv/bridge_loop_avoidance.c
index ef39aabdb694..4fb01108e5f5 100644
--- a/net/batman-adv/bridge_loop_avoidance.c
+++ b/net/batman-adv/bridge_loop_avoidance.c
@@ -803,6 +803,8 @@ static void batadv_bla_del_claim(struct batadv_priv *bat_priv,
 				 const u8 *mac, const unsigned short vid)
 	struct batadv_bla_claim search_claim, *claim;
+	struct batadv_bla_claim *claim_removed_entry;
+	struct hlist_node *claim_removed_node;
 	ether_addr_copy(search_claim.addr, mac);
 	search_claim.vid = vid;
@@ -813,10 +815,18 @@ static void batadv_bla_del_claim(struct batadv_priv *bat_priv,
 	batadv_dbg(BATADV_DBG_BLA, bat_priv, "%s(): %pM, vid %d\n", __func__,
 		   mac, batadv_print_vid(vid));
-	batadv_hash_remove(bat_priv->bla.claim_hash, batadv_compare_claim,
-			   batadv_choose_claim, claim);
-	batadv_claim_put(claim); /* reference from the hash is gone */
+	claim_removed_node = batadv_hash_remove(bat_priv->bla.claim_hash,
+						batadv_compare_claim,
+						batadv_choose_claim, claim);
+	if (!claim_removed_node)
+		goto free_claim;
+	/* reference from the hash is gone */
+	claim_removed_entry = hlist_entry(claim_removed_node,
+					  struct batadv_bla_claim, hash_entry);
+	batadv_claim_put(claim_removed_entry);
 	/* don't need the reference from hash_find() anymore */


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