From nobody Fri Dec 19 12:50:32 2025 Received: from mailgate01.uberspace.is (mailgate01.uberspace.is [95.143.172.20]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2AAFA2FE068 for ; Sat, 6 Dec 2025 16:26:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.143.172.20 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765038381; cv=none; b=fGT3oRoCES8mhrTZD7tnWvqAwEU8aY3HJSw+VWgjIjVQz6ARgQLnOxfgwWiNwtCl7FL5DZ54USkuc7QovnB5QdZ8HQ294tBxa8y+/KclQk3v1hfQ51whShDeUj+0QPIQp5m/hauCA9cRSpK2NA485grx0bHOIq0eK+UVBdG/H0Q= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765038381; c=relaxed/simple; bh=oY2ka5lja8UpTFcpu2gZKgfaOGa68I0bntBzjHS9b8k=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=hYPi6DikDBbSsLyjLKZOhAvK0QJrB2l+FAtF924qkCx8p1MurmE7nItXPVZZtS+7diKRGMoWN8nOjm5Q5JAhxjrhQooMlc0UDEccQhMlIcUF0c30ux6UOkZWzBryIFQDl/f3Nl89eB47yOI4AtqFrxMGIA7uRZbEaQJoHxm8HVY= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=david-bauer.net; spf=pass smtp.mailfrom=david-bauer.net; dkim=pass (4096-bit key) header.d=david-bauer.net header.i=@david-bauer.net header.b=wINfV37U; arc=none smtp.client-ip=95.143.172.20 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=david-bauer.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=david-bauer.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (4096-bit key) header.d=david-bauer.net header.i=@david-bauer.net header.b="wINfV37U" Received: from perseus.uberspace.de (perseus.uberspace.de [95.143.172.134]) by mailgate01.uberspace.is (Postfix) with ESMTPS id 590EE60D07 for ; Sat, 06 Dec 2025 17:26:10 +0100 (CET) Received: (qmail 16583 invoked by uid 988); 6 Dec 2025 16:26:10 -0000 Authentication-Results: perseus.uberspace.de; auth=pass (plain) Received: from unknown (HELO unkown) (::1) by perseus.uberspace.de (Haraka/3.0.1) with ESMTPSA; Sat, 06 Dec 2025 17:26:10 +0100 From: David Bauer To: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , "R. Parameswaran" Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net] l2tp: account for IP version in SKB headroom Date: Sat, 6 Dec 2025 17:26:01 +0100 Message-ID: <20251206162603.24900-1-mail@david-bauer.net> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Rspamd-Bar: / X-Rspamd-Report: SUSPICIOUS_RECIPS(1.5) BAYES_HAM(-3) MID_CONTAINS_FROM(1) MIME_GOOD(-0.1) R_MISSING_CHARSET(0.5) X-Rspamd-Score: -0.1 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=david-bauer.net; s=uberspace; h=from:to:cc:subject:date; bh=oY2ka5lja8UpTFcpu2gZKgfaOGa68I0bntBzjHS9b8k=; b=wINfV37UHZ4TMH/IR8ttaWc5wP9+Hyx2xTYANNdPHP2Fq3TCxj6aecY+07GCXj6BIdSiS9TyYD +jZptlE1NwPSGoVzWmd4XCMNmYu5b7IM5GkjJ25bh5eNSf6m9Wys60Ba4nN2YMxMKy9QqvY2Zdnh ptemAZ0rMEAcl56dAW15QLVmSa18Vz4XHYo1o5p/NrWs1hsVd3F4+3oPhix6vVEWlxgeEZ2Mx/Vd gfMbEsylEs7I32WYe2z2Fm6TB30fz+kbBC7VHqLt/J9GrQONey6JabAjbRIpuXet8zx8IHyHbjDS ee4gFubRTG/7dlq/tntAwyxGXow/9jxalbHvkxufsQMQkPIFyIOlvbPA4yItAXrajTnbGu5hlYrW ZP9JepYLX7/wBEDMvxdVvORvn2jzVppSN9CUJyOBo4sAh28KI08YMXO09A9ktKJzzyDlp50MsxcA zELbXyThO1ghMgzd15OhbIH349CmUpHvqBGien1KMR/O0xOFrglzN5AsmeTJDdCANWFXBHYmFRnr hyfJRiNj8Vb9BZ1qn/Vi+3dnGSLakEa5+j5m1HX6a/OggiN6fjLSR397Xowu2QwwVQK61iGm9dNZ XYIi1qKc+/jIvAvHOsXzB5VmxXYgSATKVPi4DaAqHgHKJ+1BojyecaqBlN9HirAv1mG5gFu2IqtX I= Content-Type: text/plain; charset="utf-8" Account for the IP version of the tunnel when accounting skb headroom on xmit. This avoids having to potentially copy the skb a second time down the stack due to allocating not enough space for IPv6 headers in case the tunnel uses IPv6. Fixes: b784e7ebfce8 ("L2TP:Adjust intf MTU, add underlay L3, L2 hdrs.") Signed-off-by: David Bauer --- net/l2tp/l2tp_core.c | 3 ++- net/l2tp/l2tp_core.h | 1 + net/l2tp/l2tp_eth.c | 9 ++------- 3 files changed, 5 insertions(+), 8 deletions(-) diff --git a/net/l2tp/l2tp_core.c b/net/l2tp/l2tp_core.c index 687c1366a4d0f..b07b4861f2f59 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1234,7 +1234,7 @@ static int l2tp_xmit_core(struct l2tp_session *sessio= n, struct sk_buff *skb, uns * make room. Adjust truesize. */ uhlen =3D (tunnel->encap =3D=3D L2TP_ENCAPTYPE_UDP) ? sizeof(*uh) : 0; - headroom =3D NET_SKB_PAD + sizeof(struct iphdr) + uhlen + session->hdr_le= n; + headroom =3D NET_SKB_PAD + tunnel->l3_overhead + uhlen + session->hdr_len; if (skb_cow_head(skb, headroom)) { kfree_skb(skb); return NET_XMIT_DROP; @@ -1680,6 +1680,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, = struct net *net, } =20 sk->sk_allocation =3D GFP_ATOMIC; + tunnel->l3_overhead =3D kernel_sock_ip_overhead(sk); release_sock(sk); =20 sock_hold(sk); diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h index ffd8ced3a51ff..aab574376d95f 100644 --- a/net/l2tp/l2tp_core.h +++ b/net/l2tp/l2tp_core.h @@ -167,6 +167,7 @@ struct l2tp_tunnel { u32 tunnel_id; u32 peer_tunnel_id; int version; /* 2=3D>L2TPv2, 3=3D>L2TPv3 */ + int l3_overhead; /* IP header overhead */ =20 char name[L2TP_TUNNEL_NAME_MAX]; /* for logging */ enum l2tp_encap_type encap; diff --git a/net/l2tp/l2tp_eth.c b/net/l2tp/l2tp_eth.c index cf0b66f4fb29b..709e1fb1b2e3c 100644 --- a/net/l2tp/l2tp_eth.c +++ b/net/l2tp/l2tp_eth.c @@ -187,7 +187,6 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tun= nel, struct net_device *dev) { unsigned int overhead =3D 0; - u32 l3_overhead =3D 0; u32 mtu; =20 /* if the encap is UDP, account for UDP header size */ @@ -196,11 +195,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tu= nnel, dev->needed_headroom +=3D sizeof(struct udphdr); } =20 - lock_sock(tunnel->sock); - l3_overhead =3D kernel_sock_ip_overhead(tunnel->sock); - release_sock(tunnel->sock); - - if (l3_overhead =3D=3D 0) { + if (tunnel->l3_overhead =3D=3D 0) { /* L3 Overhead couldn't be identified, this could be * because tunnel->sock was NULL or the socket's * address family was not IPv4 or IPv6, @@ -211,7 +206,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tun= nel, /* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr * UDP overhead, if any, was already factored in above. */ - overhead +=3D session->hdr_len + ETH_HLEN + l3_overhead; + overhead +=3D session->hdr_len + ETH_HLEN + tunnel->l3_overhead; =20 mtu =3D l2tp_tunnel_dst_mtu(tunnel) - overhead; if (mtu < dev->min_mtu || mtu > dev->max_mtu) --=20 2.51.0