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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH net-next 1/2] l2tp: account for IP version in SKB headroom Date: Fri, 27 Feb 2026 23:07:37 +0100 Message-ID: <20260227220740.11928-1-mail@david-bauer.net> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Bar: - X-Rspamd-Report: MID_CONTAINS_FROM(1) BAYES_HAM(-2.999999) MIME_GOOD(-0.1) R_MISSING_CHARSET(0.5) X-Rspamd-Score: -1.599999 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=david-bauer.net; s=uberspace; h=from:to:cc:subject:date; bh=TTfI44tvuFwsGVLvU35bqIiczRST6P5VXzFUFdVzMys=; b=LRBsSFV/tQIaEZ5IpwS8nn6+fHpAG05Pty3FtVIJsAeuhhb7yep1eHIKy7PlmB7lAjReIRDEnf e4/RMWvZ+b+OPKhAN9ex+CSA/8MkcYB/JRW4IJsmlpaENdmmNNiAQROB7NbM+WECa2xhw6P7Xauf p6zX1Vf4PGeJlR+Hf5/xp2q/8QfUjSo8TwfONHzfJS95Li7F8UO3Bq4mHnq/PZNn/8pv4eqSGJkn 0pZ+mBOdErLocu7VJzNwas/u6aeGCq1bqPePdATapyIKbVErj++SrT1MHm6uCbrU3PSUXxnaN03Q e1QyOsKPAHJXTjArjY3JEs+cJ7hHHDQt3zT1XBljoY0t7799lhy1d6+CClaZSxCiKvSGJM9dk5no +WEF1iBEIjFm4NSe48ZK2gCQm/NiOv1chQuYPxtzGlEUbOn2kURYnWKE0opuJouEC6yjXAsQ+XWC fZkTxifkbdbqeYa8bmpprWk/s6gqCHOJVegQaYCXlxevHc+YCN3A8HhGVHLYetsNDDJNYktccFAd F/zcbny/KE//6mZy9sxzEDUnfzH1kTy5puDes2mxv/6z38GPOj9xPNJgCyfWJ5tkG64FdZt+l9Cr HEOPMijBgta522JAvac6HAswEQzlnlS1fZ34EfZgIhFLJ5aW0Vl9ootGYpnUva89hJi8+wPZFLAB w= 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. 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 c89ae52764b89..bb19c11b0af8e 100644 --- a/net/l2tp/l2tp_core.c +++ b/net/l2tp/l2tp_core.c @@ -1236,7 +1236,7 @@ static int l2tp_xmit_core(struct l2tp_session *session, struct sk_buff *skb, uns * make room. Adjust truesize. */ uhlen = (tunnel->encap == L2TP_ENCAPTYPE_UDP) ? sizeof(*uh) : 0; - headroom = NET_SKB_PAD + sizeof(struct iphdr) + uhlen + session->hdr_len; + headroom = NET_SKB_PAD + tunnel->l3_overhead + uhlen + session->hdr_len; if (skb_cow_head(skb, headroom)) { kfree_skb(skb); return NET_XMIT_DROP; @@ -1682,6 +1682,7 @@ int l2tp_tunnel_register(struct l2tp_tunnel *tunnel, struct net *net, } sk->sk_allocation = GFP_ATOMIC; + tunnel->l3_overhead = kernel_sock_ip_overhead(sk); release_sock(sk); 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=>L2TPv2, 3=>L2TPv3 */ + int l3_overhead; /* IP header overhead */ 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 a4956ef9574cc..9e5f9deac08cf 100644 --- a/net/l2tp/l2tp_eth.c +++ b/net/l2tp/l2tp_eth.c @@ -188,7 +188,6 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel, struct net_device *dev) { unsigned int overhead = 0; - u32 l3_overhead = 0; u32 mtu; /* if the encap is UDP, account for UDP header size */ @@ -197,11 +196,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel, dev->needed_headroom += sizeof(struct udphdr); } - lock_sock(tunnel->sock); - l3_overhead = kernel_sock_ip_overhead(tunnel->sock); - release_sock(tunnel->sock); - - if (l3_overhead == 0) { + if (tunnel->l3_overhead == 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, @@ -212,7 +207,7 @@ static void l2tp_eth_adjust_mtu(struct l2tp_tunnel *tunnel, /* Adjust MTU, factor overhead - underlay L3, overlay L2 hdr * UDP overhead, if any, was already factored in above. */ - overhead += session->hdr_len + ETH_HLEN + l3_overhead; + overhead += session->hdr_len + ETH_HLEN + tunnel->l3_overhead; mtu = l2tp_tunnel_dst_mtu(tunnel) - overhead; if (mtu < dev->min_mtu || mtu > dev->max_mtu) -- 2.51.0