From 94d27005016be15ffc638b2ecbc4d58805ad7b48 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Sat, 2 May 2026 19:47:11 +0200 Subject: [PATCH] batman-adv: tt: fix TOCTOU race for reported vlans The local TT based TVLV is generated by first checking the number of VLANs which have at least one TT entry. A new buffer with the correct size for the VLANs is then allocated. Only then, the list of VLANs s used to fill the VLAN entries in the buffer. During this time, the meshif_vlan_list_lock is held. But the actual number of TT entries of each VLAN can still increase during this time - just not the number of VLANs in the list. But the prefilter used in the buffer size calculation might still cause an increase of the number of VLANs which need to be stored. Simply because a VLAN might now suddenly have at least one entry when it had none in the pre-alloc check - and then needs to occupy space which was not allocated. It is better to overestimate the buffer size at the beginning and then fill the buffer only with the VLANs which are not empty. Cc: stable@kernel.org Fixes: 16116dac2339 ("batman-adv: prevent TT request storms by not sending inconsistent TT TLVLs") Signed-off-by: Sven Eckelmann --- net/batman-adv/translation-table.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/net/batman-adv/translation-table.c b/net/batman-adv/translation-table.c index 06548dae1039..f009cbf8a276 100644 --- a/net/batman-adv/translation-table.c +++ b/net/batman-adv/translation-table.c @@ -887,11 +887,8 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv, spin_lock_bh(&bat_priv->meshif_vlan_list_lock); hlist_for_each_entry(vlan, &bat_priv->meshif_vlan_list, list) { vlan_entries = atomic_read(&vlan->tt.num_entries); - if (vlan_entries < 1) - continue; - - num_vlan++; total_entries += vlan_entries; + num_vlan++; } change_offset = struct_size(*tt_data, vlan_data, num_vlan); @@ -916,6 +913,7 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv, (*tt_data)->num_vlan = htons(num_vlan); tt_vlan = (*tt_data)->vlan_data; + num_vlan = 0; hlist_for_each_entry(vlan, &bat_priv->meshif_vlan_list, list) { vlan_entries = atomic_read(&vlan->tt.num_entries); if (vlan_entries < 1) @@ -926,8 +924,15 @@ batadv_tt_prepare_tvlv_local_data(struct batadv_priv *bat_priv, tt_vlan->reserved = 0; tt_vlan++; + num_vlan++; } + /* recalculate in case number of VLANs reduced */ + change_offset = struct_size(*tt_data, vlan_data, num_vlan); + tvlv_len = *tt_len + change_offset; + + (*tt_data)->num_vlan = htons(num_vlan); + tt_change_ptr = (u8 *)*tt_data + change_offset; *tt_change = (struct batadv_tvlv_tt_change *)tt_change_ptr;