• Sven Eckelmann's avatar
    batman-adv: Reduce claim hash refcnt only for removed entry · 4ba104f4
    Sven Eckelmann authored
    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
    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: 23721387 ("batman-adv: add basic bridge loop avoidance code")
    Signed-off-by: default avatarSven Eckelmann <sven@narfation.org>
    Signed-off-by: default avatarSimon Wunderlich <sw@simonwunderlich.de>
    4ba104f4
bridge_loop_avoidance.c 70.3 KB