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

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


The following commit has been merged in the master branch:
commit 3d65b9accab4a7ed5038f6df403fbd5e298398c7
Author: Sven Eckelmann <sven at narfation.org>
Date:   Sat Feb 23 14:27:10 2019 +0100

    batman-adv: Reduce tt_local 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_local_remove 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: ef72706a0543 ("batman-adv: protect tt_local_entry from concurrent delete events")
    Signed-off-by: Sven Eckelmann <sven at narfation.org>
    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 f73d79139ae7..b5cfc5068a90 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -1337,9 +1337,10 @@ u16 batadv_tt_local_remove(struct batadv_priv *bat_priv, const u8 *addr,
 			   unsigned short vid, const char *message,
 			   bool roaming)
 {
+	struct batadv_tt_local_entry *tt_removed_entry;
 	struct batadv_tt_local_entry *tt_local_entry;
 	u16 flags, curr_flags = BATADV_NO_FLAGS;
-	void *tt_entry_exists;
+	struct hlist_node *tt_removed_node;
 
 	tt_local_entry = batadv_tt_local_hash_find(bat_priv, addr, vid);
 	if (!tt_local_entry)
@@ -1368,15 +1369,18 @@ u16 batadv_tt_local_remove(struct batadv_priv *bat_priv, const u8 *addr,
 	 */
 	batadv_tt_local_event(bat_priv, tt_local_entry, BATADV_TT_CLIENT_DEL);
 
-	tt_entry_exists = batadv_hash_remove(bat_priv->tt.local_hash,
+	tt_removed_node = batadv_hash_remove(bat_priv->tt.local_hash,
 					     batadv_compare_tt,
 					     batadv_choose_tt,
 					     &tt_local_entry->common);
-	if (!tt_entry_exists)
+	if (!tt_removed_node)
 		goto out;
 
-	/* extra call to free the local tt entry */
-	batadv_tt_local_entry_put(tt_local_entry);
+	/* drop reference of remove hash entry */
+	tt_removed_entry = hlist_entry(tt_removed_node,
+				       struct batadv_tt_local_entry,
+				       common.hash_entry);
+	batadv_tt_local_entry_put(tt_removed_entry);
 
 out:
 	if (tt_local_entry)

-- 
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