[PATCH net] l2tp: account for IP version in SKB headroom
From: David Bauer <hidden>
Date: 2025-12-06 16:26:17
Also in:
lkml
Subsystem:
networking [general], the rest · Maintainers:
"David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds
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 <redacted>
---
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 *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;
@@ -1680,6 +1680,7 @@ 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 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 *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 */
@@ -196,11 +195,7 @@ 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,
@@ -211,7 +206,7 @@ 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