Repository : ssh://git@open-mesh.org/batman-adv

On branch : master

commit 0c86a0511e97de502276900c5d6f22b09e042d21 Author: Sven Eckelmann sven@narfation.org Date: Sat Feb 23 15:09:05 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: af912d77181f ("batman-adv: protect tt_local_entry from concurrent delete events") Signed-off-by: Sven Eckelmann sven@narfation.org

0c86a0511e97de502276900c5d6f22b09e042d21 net/batman-adv/translation-table.c | 14 +++++++++----- 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c index f73d7913..b5cfc506 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)