From 566f8d5c8a443f2dd69c5460fdec43ed1c870c65 Mon Sep 17 00:00:00 2001 From: Dmitry Safonov Date: Thu, 9 Oct 2025 16:02:19 +0100 Subject: [PATCH] net/ip6_tunnel: Prevent perpetual tunnel growth [ Upstream commit 21f4d45eba0b2dcae5dbc9e5e0ad08735c993f16 ] Similarly to ipv4 tunnel, ipv6 version updates dev->needed_headroom, too. While ipv4 tunnel headroom adjustment growth was limited in commit 5ae1e9922bbd ("net: ip_tunnel: prevent perpetual headroom growth"), ipv6 tunnel yet increases the headroom without any ceiling. Reflect ipv4 tunnel headroom adjustment limit on ipv6 version. Credits to Francesco Ruggeri, who was originally debugging this issue and wrote local Arista-specific patch and a reproducer. Fixes: 8eb30be0352d ("ipv6: Create ip6_tnl_xmit") Cc: Florian Westphal Cc: Francesco Ruggeri Signed-off-by: Dmitry Safonov Link: https://patch.msgid.link/20251009-ip6_tunnel-headroom-v2-1-8e4dbd8f7e35@arista.com Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- include/net/ip_tunnels.h | 15 +++++++++++++++ net/ipv4/ip_tunnel.c | 14 -------------- net/ipv6/ip6_tunnel.c | 3 +-- 3 files changed, 16 insertions(+), 16 deletions(-) diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h index 3a04e2ccfb39..d2945ec5aba2 100644 --- a/include/net/ip_tunnels.h +++ b/include/net/ip_tunnels.h @@ -454,6 +454,21 @@ void iptunnel_xmit(struct sock *sk, struct rtable *rt, struct sk_buff *skb, struct metadata_dst *iptunnel_metadata_reply(struct metadata_dst *md, gfp_t flags); +static inline void ip_tunnel_adj_headroom(struct net_device *dev, + unsigned int headroom) +{ + /* we must cap headroom to some upperlimit, else pskb_expand_head + * will overflow header offsets in skb_headers_offset_update(). + */ + const unsigned int max_allowed = 512; + + if (headroom > max_allowed) + headroom = max_allowed; + + if (headroom > READ_ONCE(dev->needed_headroom)) + WRITE_ONCE(dev->needed_headroom, headroom); +} + int iptunnel_handle_offloads(struct sk_buff *skb, int gso_type_mask); static inline int iptunnel_pull_offloads(struct sk_buff *skb) diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 906c37c7f80d..38cace81bfa2 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -560,20 +560,6 @@ static int tnl_update_pmtu(struct net_device *dev, struct sk_buff *skb, return 0; } -static void ip_tunnel_adj_headroom(struct net_device *dev, unsigned int headroom) -{ - /* we must cap headroom to some upperlimit, else pskb_expand_head - * will overflow header offsets in skb_headers_offset_update(). - */ - static const unsigned int max_allowed = 512; - - if (headroom > max_allowed) - headroom = max_allowed; - - if (headroom > READ_ONCE(dev->needed_headroom)) - WRITE_ONCE(dev->needed_headroom, headroom); -} - void ip_md_tunnel_xmit(struct sk_buff *skb, struct net_device *dev, u8 proto, int tunnel_hlen) { diff --git a/net/ipv6/ip6_tunnel.c b/net/ipv6/ip6_tunnel.c index 5319093d9aa6..c79e6c032b30 100644 --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -1201,8 +1201,7 @@ route_lookup: */ max_headroom = LL_RESERVED_SPACE(dst->dev) + sizeof(struct ipv6hdr) + dst->header_len + t->hlen; - if (max_headroom > READ_ONCE(dev->needed_headroom)) - WRITE_ONCE(dev->needed_headroom, max_headroom); + ip_tunnel_adj_headroom(dev, max_headroom); err = ip6_tnl_encap(skb, t, &proto, fl6); if (err)