From 4cd6d3a4b96a8576f1fed8f9f9f17c2dc2978e0c Mon Sep 17 00:00:00 2001 From: Sven Eckelmann Date: Wed, 10 Jun 2026 13:33:19 +0200 Subject: [PATCH] batman-adv: ensure bcast is writable before modifying TTL Before batman-adv is allowed to write to an skb, it either has to have its own copy of the skb or used skb_cow() to ensure that the data part is not shared. The old implementation used a shared queue and created copies before attempting to write to it. But with the new implementation, the broadcast packet is already modified when it gets received. Potentially writing to shared buffers in this process. Adding a skb_cow() right before this operation avoids this and can at the same time prepare it for the modifications required to rebroadcast the packet. Cc: stable@kernel.org Fixes: 3f69339068f9 ("batman-adv: bcast: queue per interface, if needed") Signed-off-by: Sven Eckelmann --- net/batman-adv/routing.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/net/batman-adv/routing.c b/net/batman-adv/routing.c index cd4368b846ad..7b4acd1ad991 100644 --- a/net/batman-adv/routing.c +++ b/net/batman-adv/routing.c @@ -1191,6 +1191,12 @@ int batadv_recv_bcast_packet(struct sk_buff *skb, if (batadv_is_my_mac(bat_priv, bcast_packet->orig)) goto free_skb; + /* create a copy of the skb, if needed, to modify it. */ + if (skb_cow(skb, ETH_HLEN) < 0) + goto free_skb; + + bcast_packet = (struct batadv_bcast_packet *)skb->data; + if (bcast_packet->ttl-- < 2) goto free_skb;