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

batman at open-mesh.org batman at open-mesh.org
Sat Mar 30 00:19:31 CET 2019


The following commit has been merged in the master branch:
commit f131a56880d10932931e74773fb8702894a94a75
Author: Sven Eckelmann <sven at narfation.org>
Date:   Sat Feb 23 14:27:10 2019 +0100

    batman-adv: Reduce tt_global 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_tt_global_free 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
    reduced.
    
    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: 7683fdc1e886 ("batman-adv: protect the local and the global trans-tables with rcu")
    Reported-by: Martin Weinelt <martin at linuxlounge.net>
    Signed-off-by: Sven Eckelmann <sven at narfation.org>
    Acked-by: Antonio Quartulli <a at unstable.cc>
    Signed-off-by: Simon Wunderlich <sw at simonwunderlich.de>

diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c
index b5cfc5068a90..26c4e2493ddf 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -616,14 +616,26 @@ static void batadv_tt_global_free(struct batadv_priv *bat_priv,
 				  struct batadv_tt_global_entry *tt_global,
 				  const char *message)
 {
+	struct batadv_tt_global_entry *tt_removed_entry;
+	struct hlist_node *tt_removed_node;
+
 	batadv_dbg(BATADV_DBG_TT, bat_priv,
 		   "Deleting global tt entry %pM (vid: %d): %s\n",
 		   tt_global->common.addr,
 		   batadv_print_vid(tt_global->common.vid), message);
 
-	batadv_hash_remove(bat_priv->tt.global_hash, batadv_compare_tt,
-			   batadv_choose_tt, &tt_global->common);
-	batadv_tt_global_entry_put(tt_global);
+	tt_removed_node = batadv_hash_remove(bat_priv->tt.global_hash,
+					     batadv_compare_tt,
+					     batadv_choose_tt,
+					     &tt_global->common);
+	if (!tt_removed_node)
+		return;
+
+	/* drop reference of remove hash entry */
+	tt_removed_entry = hlist_entry(tt_removed_node,
+				       struct batadv_tt_global_entry,
+				       common.hash_entry);
+	batadv_tt_global_entry_put(tt_removed_entry);
 }
 
 /**

-- 
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