From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=170.10.133.124 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1792505065; b=MjEpWPXJE09zMDb6WaIiHRCsyeYxguno+htRRJWLUA1TZTqpy0X8saE9G883GrTUXfa9 OORZBRikbZTs3r1RHYEs2mY/Twb4zPpjyy/NX57uQQvF1HzuGR6flU6RP+9z5/JoMgsDF 2JeDJ2hgJwIhszkVza0KsQYB3XW9Ki8Sfms3ZedkXfE48Hs0ynuqklSCmkGLNbes3Z2xk hMjmIVSDvnMaRIZjpOx8q7L+X36zuuE+Pc1JUh0ucba8uxhNWIPLfAQH2MwhUiCbPwibq 4yQMtgQYZVBvrawBJ01nvQ7JJMgWU8p8iKDopXOIwFuJJtrsYSGQIQkHebB9+xt1HgQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792505065; h=DMARC-Filter:DKIM-Signature:Received:X-MC-Unique: X-Mimecast-MFC-AGG-ID:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received: X-Received:Received:Date:From:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition: Content-Transfer-Encoding:In-Reply-To; bh=VTSXONY++MHAhLW+7kA48dz0Wy/1YW5a9nSo3Jvds/4=; b=TIn7JB4/8wQkiRjZVK8B3KTRkwm2t/+Wzsp0rmW6ctei2Ip5xczdzzxhkA02klMhWVs8 8XJnwC3HVo5Msfgeixo/yI5GFDqdsZ0a9yT+NFfhO00ul51KulIs9bJ4XcgmoO6lIbyad +7zAlUgnChIdWYEIT0uATiZ0al5kIQEZ4/MeDmpUTFMOh45UNYwlvN/Ai5ObF6jSVYAe8 xd8IuWld7AiC+kWCNJP+rrn4mJDlyMaVgGhpiK+XUNnEhPD29m2XXZKtYtSGuF89JnoBu NW2AKlkYcpYdrRJSY0xXY2Iz3WSecx7A3n64oAbnTt5wEQMNsnCPjOWneKBP9Mv93hg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=d1YoMmCE; dkim=pass header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=google header.b=jD3Ku7t5; arc=none smtp.remote-ip=170.10.133.124 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C5A35606A31E for ; Tue, 20 Oct 2026 14:04:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org C5A35606A31E Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=mimecast20190719 header.b=d1YoMmCE; dkim=pass (2048-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=google header.b=jD3Ku7t5 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792505063; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=VTSXONY++MHAhLW+7kA48dz0Wy/1YW5a9nSo3Jvds/4=; b=d1YoMmCEYMXsUc8UpRWc2vm4Z0difS/OnP6W+4mgxE4foxt66RTfx804iKsbRBehOluh3o su7REJEcUv+vpsmaP/Ew8AHLLxWOAx6DAEoeF/0hFIYsUyMG2sZs10tWz7LHUJHPDxTitu QNM1ogfuxx3Pd25+L992j922ixtcHKE= Received: from mail-wm1-f72.google.com (mail-wm1-f72.google.com [209.85.128.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-36-s76RzFYxPAGWPtU5YwR01Q-1; Tue, 20 Oct 2026 10:04:22 -0400 X-MC-Unique: s76RzFYxPAGWPtU5YwR01Q-1 X-Mimecast-MFC-AGG-ID: s76RzFYxPAGWPtU5YwR01Q_1792505061 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-495689bfcc8so21991045e9.1 for ; Tue, 20 Oct 2026 07:04:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1792505061; x=1793109861; darn=vger.kernel.org; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to:content-type; bh=VTSXONY++MHAhLW+7kA48dz0Wy/1YW5a9nSo3Jvds/4=; b=jD3Ku7t53da2jDbwWAd3mnSS/fhq2YOw/BNvuENil4PTdqhIaC6xkmeQHh8XWV6ush SEEM4hj/niIDEaUFc2gJIBzf9/IU72mM9htxfduVH6owTsXNxi6u3/qlJi5vdpjwWBna OQgVbN/PQYIeJvAz5r03IlGB/OMHgf/QjprM3HDOWO+3tYVfdGzXU2cCiF+Ixl+xIMxS eIMjODXMkWJDu6vgF8R8BPfVu2lddbbDz9F1m2Pg5hY4Qx3bjqI27PhaGv9f/f1IK5rF gVICSTUt0DoLAqkM7Ym0GzMx4N7P7Eg+6qo2teQQHIp7uXmFp/AiEyWS30AdHbIWIkgT IuGg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792505061; x=1793109861; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=VTSXONY++MHAhLW+7kA48dz0Wy/1YW5a9nSo3Jvds/4=; b=f5+RUQhT5MeMabaRLZUekEswkM8mGjfat+CqduwVVNK8V117IVgss8eT9mCtP77f3/ wyKRFBWzU8ZQnVZ5O0VgOHLpzknscUmayzZpPVxmCLvw0YBFDtWx3jC32f8sCz6LA/R2 fKunkc9bwkmP9zZ8V1KuxmJjy0NcuxMLaKb5Pla47Vbgfu0C9KCU9VWQZyHcSKHavf8j rDsqqF6rsmLR8xWuyi4UyXoxOA2koYcKrVZRAfykrlWI5TVgb+eBGGKDWYJEJCRivv1R EvF96EnVzBjRuEIzv1Vkvfveeji54JXnirnIdenORqKqYYbWXwKEIGMLRWmqy0WCsVx+ S8eg== X-Forwarded-Encrypted: i=1; AKwUvBytUjP2zgxC2FUfBYCRVYADjjKQZZowcpD7hzH6QK7l5hHnBXZz3plMSplCW/WQlbFk470SSBY=@vger.kernel.org X-Gm-Message-State: AFq9FYIiWJ0+0ekfwhVnxxF9LC8bLfrkTDZtbqJItRmE0wVu7sCEsePl 1eJgSDPlH++y8AqMYXg7MkE9dbkZ1HzccAkNdBDBTU4PBBGAU0a+47YICUeD7gkSxWVZrjK/Ojd DBW+QHtkbDaj+MJ4yGq51o5K8bmrU101C/LyhmifsBT+N0DUM6qMfSB5z/Q== X-Gm-Gg: AYBFou0QaaFVYv1kvJwGfdX4v2WXMZdlLyeBb3XtRWVmmiXDDGOuMnzJ/8OBGQtkqn5 JXzHEACcet9j0LNw5XLLdsBmyJ0tRUtqoenZu9UowlRvc0EflPlJbq3IYhF78dcoS3AMwUhIAXw Aw+z2lExMGqY3/w+kUOjuT6NqutvO7GQPjIym0qebrcHSP8mQ2njWh3DOfBy8ZRKfB6SerVMLvk H4BOl0qkQU9lR3Xj4aAJ+t+SDV08pFeOWV8fjvsPjYwjCTTK/ex7DEsNPuDgWYouRKdfryboH8i 377f09WqOVX3m6z0XzgezYb5o0c7QJlKtHAByhxe4YIn15/uascNNL+gqboM6KKvj20tVw== X-Received: by 2002:a05:600c:859a:b0:4a1:d8c5:b23f with SMTP id 5b1f17b1804b1-4a1d8c5bb82mr193418455e9.24.1792505060865; Tue, 20 Oct 2026 07:04:20 -0700 (PDT) X-Received: by 2002:a05:600c:859a:b0:4a1:d8c5:b23f with SMTP id 5b1f17b1804b1-4a1d8c5bb82mr193417665e9.24.1792505060268; Tue, 20 Oct 2026 07:04:20 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:3fd7:5300:3d6b:52a4:a23f:9d0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1f2cc0708sm68065075e9.7.2026.10.20.07.04.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Oct 2026 07:04:19 -0700 (PDT) Date: Tue, 20 Oct 2026 10:04:15 -0400 From: "Michael S. Tsirkin" To: =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= Cc: linux-kernel@vger.kernel.org, Willem de Bruijn , Chris Arges , Phil Sutter , Jason Wang , Eugenio =?iso-8859-1?Q?P=E9rez?= , Xuan Zhuo , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, virtualization@lists.linux.dev, Max Krasnyansky , Rusty Russell , Jonathan Corbet , Shuah Khan , Randy Dunlap , Simon Horman , linux-doc@vger.kernel.org Subject: Re: [PATCH net v3 6/8] net: add a sysctl to opt out of virtio net hdr checksum validation Message-ID: <20261020100349-mutt-send-email-mst@kernel.org> References: <6f23c55c6eba3e3ec6b2c7e3a80728a326ed58af.1792411304.git.mst@redhat.com> <87fqy13h97.fsf@all.your.base.are.belong.to.us> X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87fqy13h97.fsf@all.your.base.are.belong.to.us> On Mon, Oct 19, 2026 at 04:19:16PM +0200, Björn Töpel wrote: > "Michael S. Tsirkin" writes: > > > The ingress validation as implemented by the previous > > patch is stricter than what it replaced: GSO > > packets whose checksum metadata matches no transport header are > > dropped, and non-GSO ones get their checksum completed in place. > > Such packets used to pass with the metadata unvalidated, > > and with no overhead. > > > > I judge that this should not affect any deployments, but there is still > > some risk that it does. In case a deployment depends on them anyway, > > provide a per-netns switch to get the old behavior back: > > > > echo 0 > /proc/sys/net/core/virtio_net_hdr_csum_check > > > > The default is validating. > > > > Assisted-by: LLM > > Signed-off-by: Michael S. Tsirkin > > --- > > Documentation/admin-guide/sysctl/net.rst | 19 ++++++++ > > include/linux/virtio_net.h | 23 +++++++++ > > include/net/netns/core.h | 1 + > > net/core/dev.c | 6 +++ > > net/core/net_namespace.c | 1 + > > net/core/sysctl_net_core.c | 60 ++++++++++++++++++++++++ > > 6 files changed, 110 insertions(+) > > > > diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst > > index e586e17fc7a5..b1a1c4714b22 100644 > > --- a/Documentation/admin-guide/sysctl/net.rst > > +++ b/Documentation/admin-guide/sysctl/net.rst > > @@ -246,6 +246,25 @@ processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. > > Default: 1 (on) > > > > > > +virtio_net_hdr_csum_check > > +------------------------- > > + > > +When processing packets with a virtio net header (through tun, tap, a > > +packet socket or a virtio network device) that request checksum offload > > +(VIRTIO_NET_HDR_F_NEEDS_CSUM), validate the packet: complete the checksum > > +in software, or drop the packet where the header does not match it. > > + > > +When disabled, the header is trusted not to corrupt the packet, and the > > +checksum is offloaded to hardware (or not verified if it never reaches > > +hardware). This is only safe if no protocol is processing the packets. > > + > > +The setting is per network namespace, but only writable by the host > > +root: root inside a network namespace created by an unprivileged user > > +cannot disable the validation. > > + > > +Default: 1 (on) > > + > > + > > wmem_default > > ------------ > > > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > > index 97b554ef7123..25aa95c11e31 100644 > > --- a/include/linux/virtio_net.h > > +++ b/include/linux/virtio_net.h > > @@ -5,6 +5,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include > > @@ -78,6 +79,19 @@ static inline struct iphdr *virtio_net_ip4_parse(struct sk_buff *skb, > > *thoff = nhoff + iph->ihl * sizeof(u32); > > return iph; > > } > > +/* Defined in net/core/dev.c, enabled while any network namespace > > + * has net.core.virtio_net_hdr_csum_check set to 0. > > + */ > > +DECLARE_STATIC_KEY_FALSE(virtio_net_hdr_csum_check_disabled_key); > > + > > +/* Failsafe: a namespace can disable the check with > > + * net.core.virtio_net_hdr_csum_check. > > + */ > > +static inline bool virtio_net_hdr_csum_check_disabled(struct sk_buff *skb) > > +{ > > + return static_branch_unlikely(&virtio_net_hdr_csum_check_disabled_key) && > > + !READ_ONCE(dev_net(skb->dev)->core.sysctl_virtio_net_hdr_csum_check); > > +} > > > > /* Where does the L3 header start, and what protocol is it? > > * Handles Ethernet and VLAN headers; other devices use the > > @@ -179,6 +193,12 @@ virtio_net_csum_partial_ok_at_offset(struct sk_buff *skb, u8 hdr_gso_type, > > unsigned int thoff; > > int ip_proto; > > > > + /* Failsafe: a namespace opted out of the validation, > > + * trust the checksum metadata as before. > > + */ > > + if (virtio_net_hdr_csum_check_disabled(skb)) > > + return true; > > + > > if (!virtio_net_l4_start(skb, nhoff, proto, &thoff, &ip_proto)) > > return false; > > > > @@ -516,6 +536,9 @@ virtio_net_tnl_offsets_ok(struct sk_buff *skb, bool outer_isv6, > > unsigned int thoff; > > int ip_proto; > > > > + if (virtio_net_hdr_csum_check_disabled(skb)) > > + return true; > > + > > if (!virtio_net_l3_start(skb, &nhoff, &proto)) > > return false; > > if (outer_isv6 != (proto == htons(ETH_P_IPV6))) > > diff --git a/include/net/netns/core.h b/include/net/netns/core.h > > index 9ef3d70e5e9c..ae8110772c97 100644 > > --- a/include/net/netns/core.h > > +++ b/include/net/netns/core.h > > @@ -18,6 +18,7 @@ struct netns_core { > > u8 sysctl_txrehash; > > u8 sysctl_tstamp_allow_data; > > u8 sysctl_bypass_prot_mem; > > + u8 sysctl_virtio_net_hdr_csum_check; > > > > #ifdef CONFIG_PROC_FS > > struct prot_inuse __percpu *prot_inuse; > > diff --git a/net/core/dev.c b/net/core/dev.c > > index e76762e29360..d14950b1af3a 100644 > > --- a/net/core/dev.c > > +++ b/net/core/dev.c > > @@ -2389,6 +2389,12 @@ EXPORT_SYMBOL(tcf_sw_enabled_key); > > > > DEFINE_STATIC_KEY_FALSE(netstamp_needed_key); > > EXPORT_SYMBOL(netstamp_needed_key); > > + > > +/* Enabled while any network namespace has net.core.virtio_net_hdr_csum_check > > + * set to 0. > > + */ > > +DEFINE_STATIC_KEY_FALSE(virtio_net_hdr_csum_check_disabled_key); > > +EXPORT_SYMBOL(virtio_net_hdr_csum_check_disabled_key); > > #ifdef CONFIG_JUMP_LABEL > > static atomic_t netstamp_needed_deferred; > > static atomic_t netstamp_wanted; > > diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c > > index da5f881fbd3b..2d340fafba85 100644 > > --- a/net/core/net_namespace.c > > +++ b/net/core/net_namespace.c > > @@ -396,6 +396,7 @@ static __net_init void preinit_net_sysctl(struct net *net) > > net->core.sysctl_optmem_max = 128 * 1024; > > net->core.sysctl_txrehash = SOCK_TXREHASH_ENABLED; > > net->core.sysctl_tstamp_allow_data = 1; > > + net->core.sysctl_virtio_net_hdr_csum_check = 1; > > net->core.sysctl_txq_reselection = msecs_to_jiffies(1000); > > } > > > > diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c > > index eb35da3556f4..c65ff86cc5f9 100644 > > --- a/net/core/sysctl_net_core.c > > +++ b/net/core/sysctl_net_core.c > > @@ -18,6 +18,7 @@ > > #include > > #include > > #include > > +#include > > > > #include > > #include > > @@ -678,6 +679,54 @@ static struct ctl_table net_core_table[] = { > > }, > > }; > > > > +/* Defined in net/core/dev.c, declared for the gate in > > + * include/linux/virtio_net.h. > > + */ > > +DECLARE_STATIC_KEY_FALSE(virtio_net_hdr_csum_check_disabled_key); > > + > > +/* > > + * Protects changes to virtio_net_hdr_csum_check_disabled_key and each > > + * net->core.sysctl_virtio_net_hdr_csum_check. Readers don't use a lock. > > + */ > > nit: OCD doesn't like mixing old netdev comments with vanilla style... > one VVV as well. > > > +static DEFINE_MUTEX(virtio_net_hdr_csum_check_mutex); > > + > > +static int virtio_net_hdr_csum_check_sysctl(const struct ctl_table *table, > > + int write, void *buffer, > > + size_t *lenp, loff_t *ppos) > > +{ > > + struct net *net = (struct net *)table->data; > > + /* checkpatch warns but this can't be const: tmp.data is set > > below */ > > nit: Redundant comment... > > > + struct ctl_table tmp = *table; > > ...and here, can't we instead get rid of tmp, and do something like: > | u8 *value = table->data; > | u8 old, new; > > > + u8 old; > > + int ret; > > + > > + /* Root in a user namespace must not be able to weaken the > > + * validation for the network namespace it controls. > > + */ > > + if (write && !capable(CAP_NET_ADMIN)) > > + return -EPERM; > > + > > + /* > > + * Make sure virtio_net_hdr_csum_check_disabled_key counts zero values of > > + * net->core.sysctl_virtio_net_hdr_csum_check. > > + */ > > + mutex_lock(&virtio_net_hdr_csum_check_mutex); > > + > > + old = net->core.sysctl_virtio_net_hdr_csum_check; > > + tmp.data = &net->core.sysctl_virtio_net_hdr_csum_check; > > + ret = proc_dou8vec_minmax(&tmp, write, buffer, lenp, ppos); > > + if (write && !ret && old != net->core.sysctl_virtio_net_hdr_csum_check) { > > and then: > | old = READ_ONCE(*value); > | ret = proc_dou8vec_minmax(table, write, buffer, lenp, ppos); > | new = READ_ONCE(*value); > | > | if (write && !ret && old != new) { > > at least that's easier to read for me. (No blocker!) > > > Reviewed-by: Björn Töpel Thanks, I'm addressing sashiko review points, will address this in v4.