From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f200.google.com (mail-yw1-f200.google.com [209.85.128.200]) (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 B9FCF4B8DE8 for ; Wed, 16 Sep 2026 10:02:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.200 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789552939; cv=none; b=Zui27xekjUd6EqbnmLvBO3EDVi1wgehfRV82+eyLe7mLYpa9KZWPA0hNQ1NZJMZ5KclL6APNVMNv7paIWId8qELyDyVgy0malrX6+FBbc1vqyqim3fZh7ODhChHZ22sKmu5XExUUOBAf6NJBSwkMxWvqCY5zOVJOUqKzJPuzDf0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789552939; c=relaxed/simple; bh=lTeAKy2cUMECYz9XAgj6jm8FSzEY92vwbcBe9a5mHxs=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=XuoBpNc4YqeTWtEfjLDMqi7hEkbdFAHZ7kr+m+cz2XzEKb3PoyRC5xgqwjOgox/HndxdkdO+86PdBuOBom/lo7F3fCi5dfo1N8yd1spQIKeiMe3/6swazP2x/xub147mhRXyFS7CWJLIshRIwRDghgBWiLJz26HO/POjq4aL1so= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--edumazet.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=PhErvUhE; arc=none smtp.client-ip=209.85.128.200 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--edumazet.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="PhErvUhE" Received: by mail-yw1-f200.google.com with SMTP id 00721157ae682-8200c815489so64813887b3.2 for ; Wed, 16 Sep 2026 03:02:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1789552919; x=1790157719; darn=vger.kernel.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=9QagC2ovlqvpy0hNeyHV6M9kvPtIc7PIUyX82cZctBg=; b=PhErvUhEQ70LFbqV75KYnmsMG7LQJW0z4MLSQ1FiepuGeTpZyZIbOrtqKM87T809Oc 8DUUWTbHUl1UqDDl+NuROlxmG1x/vymNCkaANl1cEx7FHnoTdvXQq3mk1LJeT2/8BO2I kLRbi3A/rsEw0jIp4IundB7V5L7Tq1CLxx/YgEk8VPNKC8W4vbbqypaKxvZbKG1pdP2j zNtpZLd8Y5+Bk9RLmF3hkmeRYzgtEdk9xBHp1ssJ+K2DP6LeTCR7oUr7CIFhL9WXaKbo hSiijyefcP0h9WqhqGTAR3zEoC4NzbXPyqTtYnwsOOIfinGbxUnC+irf1S21cVlzYIh/ G+bg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789552919; x=1790157719; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=9QagC2ovlqvpy0hNeyHV6M9kvPtIc7PIUyX82cZctBg=; b=Lnec8YWGxjF97vcunVGkhlHGwBhu9R/0zD7hCnkFobRv9LTlsphTYMmd4zFX7mOJ2d Ayq8E2/POBuu61SNIfeCLVWfcdUwcVg2qBS+irfkiY2P/CyRwYT/JLD401A/Y6opQ5UF Wede9pIbatZVZRC1HG/QpD8FNlIp3VfIvX584LGurXaZbdQ8haMyS+I/P6biEycZc8qB cySV8brd17MrUXjxYj4ndMYU/21856zk3JyQ5ThrKVsST6N2bWAMmLwTzFF7YiE8ka3B zwlJTqu9va6nwrwkp6OA+o1XsoLeZFcKHn+All2SJjWNjHoeig1oz+wLtaFB6RDCim+/ KWKg== X-Forwarded-Encrypted: i=1; AKwUvBwmi3uznRvZwjyFX9b+Mkggc2weTMbovHYE6JDgD2dtjVmC9vab8q7bZG+PY9zCKkwphqee9NA=@vger.kernel.org X-Gm-Message-State: AFuF++nvadgxwqyemkE1WLueomPIsC/KrjhDBTdG56sneTB1M8bE3lbL 4YTQ6dgMqCvJujuRSWmn6WaP9omndgAYj1Abx4QHBvxcJAVubbIZ+KehyixPd7Wdp1etF6X+Ee7 xSGxPf5gd53WAaQ== X-Received: from qkcbk8-n2.prod.google.com ([2002:a05:620a:72c8:20b0:939:ff54:fa9c]) (user=edumazet job=prod-delivery.src-stubby-dispatcher) by 2002:a05:690c:f14:b0:882:31:3af9 with SMTP id 00721157ae682-8922076277cmr4830857b3.9.1789552918844; Wed, 16 Sep 2026 03:01:58 -0700 (PDT) Date: Wed, 16 Sep 2026 10:01:53 +0000 In-Reply-To: <20260916100155.1398403-1-edumazet@google.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20260912150944.3470971-1-edumazet@google.com> <20260916100155.1398403-1-edumazet@google.com> X-Mailer: git-send-email 2.55.0.1032.g73a4cd73de-goog Message-ID: <20260916100155.1398403-4-edumazet@google.com> Subject: [PATCH net v2 3/5] ip_gre: compute tunnel lengths absolutely instead of by delta From: Eric Dumazet To: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com Cc: horms@kernel.org, dsahern@kernel.org, idosch@nvidia.com, netdev@vger.kernel.org, eric.dumazet@gmail.com, Eric Dumazet Content-Type: text/plain; charset="UTF-8" ipgre_link_update() adjusts the device lengths by a difference it computes from tun_hlen alone: len = tunnel->tun_hlen; tunnel->tun_hlen = gre_calc_hlen(tunnel->parms.o_flags); len = tunnel->tun_hlen - len; tunnel->hlen = tunnel->hlen + len; But tunnel->hlen also contains encap_hlen, which ipgre_changelink() can change through ipgre_newlink_encap_setup(). Such a request leaves @len at zero: adding "encap fou" to an existing gre device keeps the MTU of a bare tunnel, while creating it with "encap fou" from the start gets the smaller MTU from ip_tunnel_bind_dev(). A difference is the wrong tool anyway: ip_tunnel_bind_dev() already assigns dev->needed_headroom from tunnel->hlen, so changing the link and the encapsulation at once is accounted twice, and ip_tunnel_encap_setup() publishes a new tunnel->hlen before the request is validated, making the next difference bogus. Recompute tunnel->hlen from tun_hlen and encap_hlen, as __gre_tunnel_init() does, and add ip_tunnel_refresh_lengths() so that ip_tunnel_bind_dev() is the only writer of dev->needed_headroom and dev->mtu. ipgre_changelink() must then refresh on its error paths too, since the new encapsulation is published by then. dev->hard_header_len is recomputed the same way, but it stays in ipgre_link_update(): for the ARPHRD_IPGRE devices installing ipgre_header_ops it is the outer IP + GRE header, which ip_tunnel_bind_dev() does not know about. Check specifically for ipgre_header_ops: gretap devices also have header_ops (eth_header_ops), where hard_header_len is the 14-byte inner Ethernet header that ip_tunnel_bind_dev() subtracts from the MTU, and commit fdafed459998 ("ip_gre: set dev->hard_header_len and dev->needed_headroom properly") wrongly adjusted hard_header_len instead of needed_headroom for them. @old_hlen survives only as a predicate telling whether the MTU became stale, never as a difference, so it can not make the lengths drift. When the header length does change, the MTU is now recomputed rather than shifted, as ip_tunnel_update() already does for a link or fwmark change. There is no memory safety issue: ipgre_xmit() cows dev->needed_headroom at tunnel entry, which always reserves sizeof(struct iphdr) + lower device headroom (>= 34 bytes after the GRE header), enough for ip_tunnel_encap() to push the FOU/GUE header before ip_tunnel_xmit() cows again for the outer IP header. Fixes: dd9d598c6657 ("ip_gre: add the support for i/o_flags update via netlink") Fixes: fdafed459998 ("ip_gre: set dev->hard_header_len and dev->needed_headroom properly") Cc: stable@vger.kernel.org Signed-off-by: Eric Dumazet --- include/net/ip_tunnels.h | 1 + net/ipv4/ip_gre.c | 55 ++++++++++++++++++++++++++++------------ net/ipv4/ip_tunnel.c | 17 +++++++++++++ 3 files changed, 57 insertions(+), 16 deletions(-) diff --git a/include/net/ip_tunnels.h b/include/net/ip_tunnels.h index 7c9aadfe8fe396da10a47e93499a97141ac04f4c..fd0396aa5039538a0391a352ace6d15f554df874 100644 --- a/include/net/ip_tunnels.h +++ b/include/net/ip_tunnels.h @@ -429,6 +429,7 @@ int ip_tunnel_newlink(struct net *net, struct net_device *dev, struct nlattr *tb[], struct ip_tunnel_parm_kern *p, __u32 fwmark); void ip_tunnel_setup(struct net_device *dev, unsigned int net_id); +void ip_tunnel_refresh_lengths(struct net_device *dev, bool set_mtu); bool ip_tunnel_netlink_encap_parms(struct nlattr *data[], struct ip_tunnel_encap *encap); diff --git a/net/ipv4/ip_gre.c b/net/ipv4/ip_gre.c index dad3d054bd15612a3ebe1cf27e6e8c5d9e6896e9..ced57cbeaad4991487e9ddb29fa18ae6a1f134fb 100644 --- a/net/ipv4/ip_gre.c +++ b/net/ipv4/ip_gre.c @@ -789,23 +789,36 @@ static netdev_tx_t gre_tap_xmit(struct sk_buff *skb, return NETDEV_TX_OK; } -static void ipgre_link_update(struct net_device *dev, bool set_mtu) +/* tunnel->hlen depends on tunnel->parms.o_flags and on tunnel->encap_hlen, + * both of which ipgre_changelink() can change. Recompute it the way + * __gre_tunnel_init() does, then let ip_tunnel_bind_dev() derive the device + * lengths from it. + * + * @old_hlen is only used to tell whether the MTU became stale, never as a + * difference to apply, so it can not make the lengths drift. It must be + * sampled before ip_tunnel_encap_setup(), which already publishes the new + * tunnel->hlen for us. + */ +static void ipgre_link_update(struct net_device *dev, bool set_mtu, + int old_hlen) { struct ip_tunnel *tunnel = netdev_priv(dev); - int len; - len = tunnel->tun_hlen; tunnel->tun_hlen = gre_calc_hlen(tunnel->parms.o_flags); - len = tunnel->tun_hlen - len; - tunnel->hlen = tunnel->hlen + len; + tunnel->hlen = tunnel->tun_hlen + tunnel->encap_hlen; - if (dev->header_ops) - dev->hard_header_len += len; - else - dev->needed_headroom += len; + /* For the ARPHRD_IPGRE devices installing ipgre_header_ops, + * dev->hard_header_len is the outer IP + GRE header, as set by + * ipgre_tunnel_init(). ip_tunnel_bind_dev() does not maintain it: + * it only subtracts it from the MTU, and only for ARPHRD_ETHER. + */ + if (dev->header_ops == &ipgre_header_ops) + dev->hard_header_len = tunnel->hlen + sizeof(struct iphdr); - if (set_mtu) - WRITE_ONCE(dev->mtu, max_t(int, dev->mtu - len, 68)); + /* Only reset a MTU that the header length just invalidated, so that + * a MTU configured by the user survives an unrelated change. + */ + ip_tunnel_refresh_lengths(dev, set_mtu && tunnel->hlen != old_hlen); if (test_bit(IP_TUNNEL_SEQ_BIT, tunnel->parms.o_flags) || (test_bit(IP_TUNNEL_CSUM_BIT, tunnel->parms.o_flags) && @@ -853,7 +866,7 @@ static int ipgre_tunnel_ctl(struct net_device *dev, ip_tunnel_flags_copy(t->parms.o_flags, p->o_flags); if (strcmp(dev->rtnl_link_ops->kind, "erspan")) - ipgre_link_update(dev, true); + ipgre_link_update(dev, true, t->hlen); } i_flags = gre_tnl_flags_to_gre_flags(p->i_flags); @@ -1474,6 +1487,7 @@ static int ipgre_changelink(struct net_device *dev, struct nlattr *tb[], struct ip_tunnel *t = netdev_priv(dev); struct ip_tunnel_parm_kern p; __u32 fwmark = t->fwmark; + int old_hlen = t->hlen; int err; if (!rtnl_dev_link_net_capable(dev, t->net)) @@ -1485,18 +1499,27 @@ static int ipgre_changelink(struct net_device *dev, struct nlattr *tb[], err = ipgre_netlink_parms(dev, data, tb, &p, &fwmark); if (err < 0) - return err; + goto link_update; err = ip_tunnel_changelink(dev, tb, &p, fwmark); if (err < 0) - return err; + goto link_update; ip_tunnel_flags_copy(t->parms.i_flags, p.i_flags); ip_tunnel_flags_copy(t->parms.o_flags, p.o_flags); - ipgre_link_update(dev, !tb[IFLA_MTU]); +link_update: + /* ipgre_newlink_encap_setup() has published a new encapsulation even + * if the rest of the request failed, so the lengths must be refreshed + * on the error paths as well. This has to come last, because + * ipgre_link_update() needs the flags copied above. + * + * IFLA_MTU only defers the MTU to do_setlink(), which rtnl_changelink() + * does not reach if we return an error, so it must not hold it back. + */ + ipgre_link_update(dev, err || !tb[IFLA_MTU], old_hlen); - return 0; + return err; } static int erspan_changelink(struct net_device *dev, struct nlattr *tb[], diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c index 2a313b18134e2f0bafd52d59d8e173fa1a084f03..dd1b2f719f21670b02bfc1cafa62689b4a28a580 100644 --- a/net/ipv4/ip_tunnel.c +++ b/net/ipv4/ip_tunnel.c @@ -326,6 +326,23 @@ static int ip_tunnel_bind_dev(struct net_device *dev) return mtu; } +/* Recompute dev->needed_headroom and dev->mtu after tunnel->hlen changed. + * + * Both are derived from tunnel->hlen, so they must be recomputed from it + * rather than adjusted by the difference: ip_tunnel_bind_dev() is also + * called from ip_tunnel_create(), ip_tunnel_newlink(), ip_tunnel_init_net() + * and ip_tunnel_update(), and a caller adding its own delta on top would + * double count it. + */ +void ip_tunnel_refresh_lengths(struct net_device *dev, bool set_mtu) +{ + int mtu = ip_tunnel_bind_dev(dev); + + if (set_mtu) + WRITE_ONCE(dev->mtu, mtu); +} +EXPORT_SYMBOL_GPL(ip_tunnel_refresh_lengths); + static struct ip_tunnel *ip_tunnel_create(struct net *net, struct ip_tunnel_net *itn, struct ip_tunnel_parm_kern *parms) -- 2.55.0.1032.g73a4cd73de-goog