From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7C541242910; Fri, 4 Sep 2026 06:00:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788501642; cv=none; b=XWw1TFwYGBOc+H9mmjFoufpRNhTy6Y2KQ+jlL7mZves6yUzva6/IJulY5CDfgDevXFVRyamr5k+lwbCbqv4ybwFZ2M8UqI02sDIMoriG5pvyWY2y1ctIvP/UrGRsYVVoj+R8P8KdFDtUtaDVivfLis3oxhRNFMSwRk0qRoBX3u0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788501642; c=relaxed/simple; bh=KREGQcF3TqHbxO3dG1ESl49I1p4/OvsxqarhPW64Roc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=MlhlvCeEuygAa76yP3K2dg2MRgkYzev2pgdGWaOacoELJ+KyS1E5+5KZA+V5bOsNXwB3ccxvb1r5devJyoJTO0LDsK3a15a5utZf01gqd7AqYNh3z22PkBrwb47YDVq4/i5B+lI7MNZ+33KQvlmH/OjWh4udeInUXlDargCMVMI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=NZbZ1Hyh; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="NZbZ1Hyh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D366A1F00A3D; Fri, 4 Sep 2026 06:00:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1788501641; bh=OcA0l2PHoPC4B01idMrCZsTDHZp0q4kEBPBdHHUt7g8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=NZbZ1HyhaA3lvAaGQssO7JWehzFdfd74TQgfxMpQzYS5p/gmAtVKOoA8LsGdx05pi gnl3AjuulcHRa7qSnFSBl5bYPdZ7sRRoejsg4k1tRTsUsW6aVTboo3gYTrex31E/5n dDwRS2LSHql0dvtAeQSVUfSL9+w7VmoTMxYhMwsU= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vega , Zhiling Zou , Ido Schimmel , Paolo Abeni Subject: [PATCH 6.18 479/552] net: cap advertised IP tunnel headroom Date: Fri, 4 Sep 2026 07:00:36 +0200 Message-ID: <20260904045801.537982343@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260904045747.813364717@linuxfoundation.org> References: <20260904045747.813364717@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Zhiling Zou commit 6b222adeb9340306e2ff97127c76117abb9b3df8 upstream. IP tunnel devices derive their advertised needed_headroom from lower output devices. A stack of user-created devices can make the derived value larger than the 16-bit skb header offsets can represent. Once IP output reserves it, skb head expansion can wrap those offsets. The runtime transmit path already caps a growing needed_headroom at 512. Apply the same cap when tunnel configuration publishes needed_headroom derived from a lower output device. Capping the advertised value is safe: IP tunnel transmit still expands the skb when a packet needs more headroom. A nonsensical stacked configuration can therefore incur an extra reallocation, but it cannot publish an unbounded reservation to upper layers. Fixes: 1a37e412a022 ("net: Use 16bits for *_headers fields of struct skbuff") Cc: stable@vger.kernel.org Reported-by: Vega Signed-off-by: Zhiling Zou Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/ba04a1fd6bfae2377607fad5d8f80f7eb80fd4c4.1786542637.git.zhilinz@nebusec.ai Signed-off-by: Paolo Abeni Signed-off-by: Greg Kroah-Hartman --- include/net/ip_tunnels.h | 11 +++++++++-- net/ipv4/ip_tunnel.c | 2 +- net/ipv6/ip6_gre.c | 7 +++++-- net/ipv6/ip6_tunnel.c | 7 +++++-- net/ipv6/sit.c | 2 +- 5 files changed, 21 insertions(+), 8 deletions(-) --- a/include/net/ip_tunnels.h +++ b/include/net/ip_tunnels.h @@ -629,8 +629,7 @@ struct metadata_dst *iptunnel_metadata_r int skb_tunnel_check_pmtu(struct sk_buff *skb, struct dst_entry *encap_dst, int headroom, bool reply); -static inline void ip_tunnel_adj_headroom(struct net_device *dev, - unsigned int headroom) +static inline unsigned int ip_tunnel_limit_headroom(unsigned int headroom) { /* we must cap headroom to some upperlimit, else pskb_expand_head * will overflow header offsets in skb_headers_offset_update(). @@ -640,6 +639,14 @@ static inline void ip_tunnel_adj_headroo if (headroom > max_allowed) headroom = max_allowed; + return headroom; +} + +static inline void ip_tunnel_adj_headroom(struct net_device *dev, + unsigned int headroom) +{ + headroom = ip_tunnel_limit_headroom(headroom); + if (headroom > READ_ONCE(dev->needed_headroom)) WRITE_ONCE(dev->needed_headroom, headroom); } --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -317,7 +317,7 @@ static int ip_tunnel_bind_dev(struct net mtu = min(tdev->mtu, IP_MAX_MTU); } - dev->needed_headroom = t_hlen + hlen; + dev->needed_headroom = ip_tunnel_limit_headroom(t_hlen + hlen); mtu -= t_hlen + (dev->type == ARPHRD_ETHER ? dev->hard_header_len : 0); if (mtu < IPV4_MIN_MTU) --- a/net/ipv6/ip6_gre.c +++ b/net/ipv6/ip6_gre.c @@ -1136,8 +1136,11 @@ static void ip6gre_tnl_link_config_route return; if (rt->dst.dev) { - dev->needed_headroom = rt->dst.dev->hard_header_len + - t_hlen; + unsigned int headroom; + + headroom = rt->dst.dev->hard_header_len + t_hlen; + headroom = ip_tunnel_limit_headroom(headroom); + dev->needed_headroom = headroom; if (set_mtu) { int mtu = rt->dst.dev->mtu - t_hlen; --- a/net/ipv6/ip6_tunnel.c +++ b/net/ipv6/ip6_tunnel.c @@ -1506,8 +1506,11 @@ static void ip6_tnl_link_config(struct i tdev = __dev_get_by_index(t->net, p->link); if (tdev) { - dev->needed_headroom = tdev->hard_header_len + - tdev->needed_headroom + t_hlen; + unsigned int headroom; + + headroom = tdev->hard_header_len + tdev->needed_headroom; + headroom += t_hlen; + dev->needed_headroom = ip_tunnel_limit_headroom(headroom); mtu = min_t(unsigned int, tdev->mtu, IP6_MAX_MTU); mtu = mtu - t_hlen; --- a/net/ipv6/sit.c +++ b/net/ipv6/sit.c @@ -1128,7 +1128,7 @@ static void ipip6_tunnel_bind_dev(struct WRITE_ONCE(dev->mtu, mtu); hlen = tdev->hard_header_len + tdev->needed_headroom; } - dev->needed_headroom = t_hlen + hlen; + dev->needed_headroom = ip_tunnel_limit_headroom(t_hlen + hlen); } static void ipip6_tunnel_update(struct ip_tunnel *t,