From d70b592551ff23747e26e74081205babf8dba9b6 Mon Sep 17 00:00:00 2001 From: David Bauer Date: Tue, 18 Nov 2025 01:16:18 +0100 Subject: [PATCH] l2tp: reset skb control buffer on xmit The L2TP stack did not reset the skb control buffer before sending the encapsulated package. In a setup with an ath10k radio and batman-adv over an L2TP tunnel massive fragmentations happen sporadically if the L2TP tunnel is established over IPv4. L2TP might reset some of the fields in the IP control buffer, but L2TP assumes the type of the control buffer to be of an IPv4 packet. In case the L2TP interface is used as a batadv hardif or the packet is an IPv6 packet, this assumption breaks. Clear the entire control buffer to avoid such mishaps altogether. Fixes: f77ae9390438 ("[PPPOL2TP]: Reset meta-data in xmit function") Signed-off-by: David Bauer Link: https://patch.msgid.link/20251118001619.242107-1-mail@david-bauer.net Signed-off-by: Paolo Abeni --- net/l2tp/l2tp_core.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 369a2f2e459c..0710281dd95a 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1246,9 +1246,9 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns else l2tp_build_l2tpv3_header(session, __skb_push(skb, session->hdr_len)); - /* Reset skb netfilter state */ - memset(&(IPCB(skb)->opt), 0, sizeof(IPCB(skb)->opt)); - IPCB(skb)->flags &= ~(IPSKB_XFRM_TUNNEL_SIZE | IPSKB_XFRM_TRANSFORMED | IPSKB_REROUTED); + /* Reset control buffer */ + memset(skb->cb, 0, sizeof(skb->cb)); + nf_reset_ct(skb); /* L2TP uses its own lockdep subclass to avoid lockdep splats caused by -- 2.47.3