3.16.72-rc1 review patch. If anyone has any objections, please let me know.
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From: Sven Eckelmann sven@narfation.org
commit f131a56880d10932931e74773fb8702894a94a75 upstream.
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@linuxlounge.net Signed-off-by: Sven Eckelmann sven@narfation.org Acked-by: Antonio Quartulli a@unstable.cc Signed-off-by: Simon Wunderlich sw@simonwunderlich.de [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/batman-adv/translation-table.c | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-)
--- a/net/batman-adv/translation-table.c +++ b/net/batman-adv/translation-table.c @@ -483,14 +483,26 @@ static void batadv_tt_global_free(struct 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_free_ref(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_free_ref(tt_removed_entry); }
/**