[B.A.T.M.A.N.] [PATCH maint] batman-adv: Avoid tt_req_node list put for unhashed entry

[Sven Eckelmann]

It can happen that a tt_req_node list entry was already removed from
tt.req_list when batadv_send_tt_request reaches the end of the function.
The reference counter was already reduced by 1 for the list entry and thus
the reference counter is not allowed to be reduced again. Otherwise, the
entry is freed too early and the next batadv_tt_req_node_put in this
function will operate on freed memory.

Fixes: cea194d90b11 ("batman-adv: improved client announcement mechanism")
Signed-off-by: Sven Eckelmann <s...@narfation.org>
---
 net/batman-adv/translation-table.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/net/batman-adv/translation-table.c 
b/net/batman-adv/translation-table.c
index 3c32f5f..7e6df7a 100644
--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -2639,11 +2639,13 @@ static bool batadv_send_tt_request(struct batadv_priv 
*bat_priv,
 out:
        if (primary_if)
                batadv_hardif_put(primary_if);
+
        if (ret && tt_req_node) {
                spin_lock_bh(&bat_priv->tt.req_list_lock);
-               /* hlist_del_init() verifies tt_req_node still is in the list */
-               hlist_del_init(&tt_req_node->list);
-               batadv_tt_req_node_put(tt_req_node);
+               if (!hlist_unhashed(&tt_req_node->list)) {
+                       hlist_del_init(&tt_req_node->list);
+                       batadv_tt_req_node_put(tt_req_node);
+               }
                spin_unlock_bh(&bat_priv->tt.req_list_lock);
        }