linux-kernel - [PATCH 4.4 40/93] batman-adv: Only put orig_node

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Message-Id: <20200319123937.892341383@linuxfoundation.org>
Date:   Thu, 19 Mar 2020 13:59:44 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sven Eckelmann <sven@...fation.org>,
        Marek Lindner <mareklindner@...mailbox.ch>,
        Antonio Quartulli <a@...table.cc>
Subject: [PATCH 4.4 40/93] batman-adv: Only put orig_node_vlan list reference when removed

From: Sven Eckelmann <sven@...fation.org>

commit 3db152093efb750bc47fd4d69355b90b18113105 upstream.

The batadv_orig_node_vlan reference counter in batadv_tt_global_size_mod
can only be reduced when the list entry was actually removed. Otherwise the
reference counter may reach zero when batadv_tt_global_size_mod is called
from two different contexts for the same orig_node_vlan but only one
context is actually removing the entry from the list.

The release function for this orig_node_vlan is not called inside the
vlan_list_lock spinlock protected region because the function
batadv_tt_global_size_mod still holds a orig_node_vlan reference for the
object pointer on the stack. Thus the actual release function (when
required) will be called only at the end of the function.

Fixes: 7ea7b4a14275 ("batman-adv: make the TT CRC logic VLAN specific")
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Marek Lindner <mareklindner@...mailbox.ch>
Signed-off-by: Antonio Quartulli <a@...table.cc>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 net/batman-adv/translation-table.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -303,9 +303,11 @@ static void batadv_tt_global_size_mod(st

 	if (atomic_add_return(v, &vlan->tt.num_entries) == 0) {
 		spin_lock_bh(&orig_node->vlan_list_lock);
-		hlist_del_init_rcu(&vlan->list);
+		if (!hlist_unhashed(&vlan->list)) {
+			hlist_del_init_rcu(&vlan->list);
+			batadv_orig_node_vlan_free_ref(vlan);
+		}
 		spin_unlock_bh(&orig_node->vlan_list_lock);
-		batadv_orig_node_vlan_free_ref(vlan);
 	}

 	batadv_orig_node_vlan_free_ref(vlan);