From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (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 19A7358E2D8 for ; Fri, 16 Oct 2026 17:51:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792173094; cv=none; b=gpKuJHjRWYXEId84+amv+9dMqnJ2uf78geJ70wGm4G1D1Q0fDnmMZ3/kLOkfKRAALQoD9VTdt+FrfcPL4hdB5Z8CfsduoiOGquy6KX2iIT3jnOlcJfJ7SzS1z4/J2G8rtCRtnW+dJk7+E74PqG9dYsirxf+C76Z4+x+VQGkY56I= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792173094; c=relaxed/simple; bh=mcjHbTCaVayfmlcAGqrGUKY2cLvBM1brbv0Ml34HCNY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=B3E/6sM5bJOS5xKPJ/7GZS03cOzyLL8rB/juKg0pPZLdGmTqXK7wFWj7MtpdNODJOqJhKaM3/U6Qh1HrR1HDCba+Ws/MswJj0BnMqFYusTaAipHLZvCFM9DP/6RPNBaiX4whYkNk/HSMgFClRY2g/xbAi5RQJzZFerXWifbj5Mc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=hEZWR9TO; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=BfleaDsC; arc=none smtp.client-ip=170.10.129.124 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) header.d=redhat.com header.i=@redhat.com header.b="hEZWR9TO"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="BfleaDsC" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792173092; 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: in-reply-to:in-reply-to:references:references; bh=W74nlXHsz1uD6EVItToAyocJ9byMIagIgs9+oTaSxM0=; b=hEZWR9TOgLF1iH4ciKnUY1IAjvpNGM8V37blixJD/tWb8LwATZpEi5Woft0Z7BMq3OmeS9 /ovz3omlWi+xBj1Xc0QCb7N4nPYafTzkIJ16wuoBZ9o1y0jxINoVXnRcBLcpO/Q4chalzI c847JSKOMvhhgsIuMsjS6uMUA3X6ghQ= Received: from mail-wr1-f71.google.com (mail-wr1-f71.google.com [209.85.221.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-259-LbcWv2cdPMemHmWqH84YNA-1; Fri, 16 Oct 2026 17:51:30 +0000 X-MC-Unique: LbcWv2cdPMemHmWqH84YNA-1 X-Mimecast-MFC-AGG-ID: LbcWv2cdPMemHmWqH84YNA_1792173088 Received: by mail-wr1-f71.google.com with SMTP id ffacd0b85a97d-48b02e93a1eso68464f8f.1 for ; Fri, 16 Oct 2026 10:51:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1792173088; x=1792777888; darn=vger.kernel.org; h=in-reply-to: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=W74nlXHsz1uD6EVItToAyocJ9byMIagIgs9+oTaSxM0=; b=BfleaDsCKFL9BHUqW/U6Sh0oe1BWsxCMN8//1ucf7R2GouhOYYoNVU83o8D/VPxhZe WZ/hLcGUS1c/FZK7uCv/XMMsc8NqtxVXFQ4ap2gPy6nVikwYgJZC+ezCiJML0r097TnW J6qHkT9u6RH7kK+IJA9GVvmWbIhIXK25KmygwnYIyRZvX2MB+cMgmscU6I6M9A+LG3rb yWUL6Dmf/XGSbbN2U281cW6gMbOZH6pUAAMz703dRE9yL4ZNyWMqjQPcWqjW6RtrzgE9 tDeErOkgMOUh92F/resIwFB7NsngkzD3w/RhxRDFsYMZi5BMdws7+0Cy2p0+homNNry8 wGsQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792173088; x=1792777888; h=in-reply-to: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=W74nlXHsz1uD6EVItToAyocJ9byMIagIgs9+oTaSxM0=; b=Ni9b2adrC3smRUQ8XBsbPAv2xuVc6XV2N6i+JMy4jnzV1HtsYvJZCLfHPsQekz10dZ KNuSr2OWiC8KRBFqbUOC2gP+b9p1hy6qTqK2NJUgeRW8r0OQnfSb/odij1c9F5ivdue7 Rvt4IdJ4Zs65j3BVXWVDr57XogmdwC8AWjxcyfnT5IEOB5BUPIquNe7iz8HCoqjI9aGq vZnL4J21leX8i00tjY4UQ4ktjCY9sc0kKXQkSAojuKShW8+0FesFobSWnUDZLSRrssEP zoT8Q34rNbzcwT4mkVPMDhLWrryr2lQ8PLcfkn7spB2XSKh2mQUNkbhGZPg6r4RVaP2Z 58Vw== X-Forwarded-Encrypted: i=1; AKwUvBzoIIVdtgk7eEHFV5dSfOIGGLkOyx6h/3tJIZ320yJ2H3PpgIMkVR6e+azykS4B+AcfvjM8cFcssAo=@vger.kernel.org X-Gm-Message-State: AFq9FYJuyvXMos0PWM4+RUZLfTBG+Hvi7husNSpdFyzwiF/PZRbXGHjH EprbMhRIrr3aQ+Ri50sD2lGasDzXzZHESF+WHNUy6LMtqHzn9/zalo+xCepDnzN+hn4NtUohivA J5JuRptl0AWZAuPvyu4eC+7ji++qJJZsZuGFwFdMWXSoLu5IgeiMglUvkcInEGA== X-Gm-Gg: AYBFou2ZrZZ4JcHGTTw46ESm/O+HomBD2Cga63/Miy1Dsr2B36ncgRkWyYt6uzUdPXS /PdReDkSHtlAJwSSZGpKSDO1mZ2f/rZUUC272JqJ75Zf+Ksa82izLHS64Mj64zfX5kWPm5Pp71e Ai309V+dIQuYXSaQqq+V0cpSaggzlIDMikzor2CuK1M53YYc4RT3c6dEcm/MGYfviSPn3VsUIZh tku6fznmBXlBVI33RmNdJ+EkaPSMFI+ZwP/l7XP7mTTYcDgxrxspMBk+pBD7FfchqUxySO2t0dU QgJ7DfNC7fZ7QcuZn3g/wkOzBZxxB3LbhhcOpbcpmgoOM03IGzeudngNR8hcuK+s6Kw1C+A= X-Received: by 2002:a05:6000:40e1:b0:48b:1c:d6e1 with SMTP id ffacd0b85a97d-48e07f9ebc9mr605349f8f.43.1792173087860; Fri, 16 Oct 2026 10:51:27 -0700 (PDT) X-Received: by 2002:a05:6000:40e1:b0:48b:1c:d6e1 with SMTP id ffacd0b85a97d-48e07f9ebc9mr605297f8f.43.1792173087273; Fri, 16 Oct 2026 10:51:27 -0700 (PDT) Received: from redhat.com ([2a06:c701:73fb:d100:601d:d7d4:d03f:527b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48dfe4d2321sm6861579f8f.19.2026.10.16.10.51.24 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Oct 2026 10:51:26 -0700 (PDT) Date: Fri, 16 Oct 2026 13:51:21 -0400 From: "Michael S. Tsirkin" To: Willem de Bruijn Cc: linux-kernel@vger.kernel.org, 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, Rusty Russell , Max Krasnyansky , Jonathan Corbet , Shuah Khan , Randy Dunlap , Simon Horman , linux-doc@vger.kernel.org Subject: Re: [PATCH net-next v2 5/7] net: add a sysctl to opt out of virtio net hdr checksum validation Message-ID: <20261016134823-mutt-send-email-mst@kernel.org> References: <20261016051827-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Oct 16, 2026 at 11:30:17AM -0400, Willem de Bruijn wrote: > Michael S. Tsirkin wrote: > > On Thu, Oct 15, 2026 at 01:50:54PM -0400, Willem de Bruijn wrote: > > > Michael S. Tsirkin wrote: > > > > 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 | 15 +++++++ > > > > 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 | 54 ++++++++++++++++++++++++ > > > > 6 files changed, 100 insertions(+) > > > > > > > > diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst > > > > index e586e17fc7a5..7f230929c37e 100644 > > > > --- a/Documentation/admin-guide/sysctl/net.rst > > > > +++ b/Documentation/admin-guide/sysctl/net.rst > > > > @@ -246,6 +246,21 @@ processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set. > > > > Default: 1 (on) > > > > > > > > > > > > +virtio_net_hdr_csum_check > > > > +------------------------- > > > > > > Make more generic, virtio_net_hdr_validate? > > > > > > In case we add more validation in the future (as we have in the past), > > > without having to introduce multiple such knobs. > > > > But it's uapi, are you sure we'll be able to change the meaning > > of an existing knob, even if we keep the name vague? > > > > > > + > > > > +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. > > > > + > > > > +Default: 1 (on) > > > > + > > > > + > > > > wmem_default > > > > ------------ > > > > > > > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > > > > index 357115ff0ec2..aa2f8ac4657c 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. > > > > + */ > > > > > > Should this be a global sysctl, rather than per netns? > > > > > > For customers I work with, it would be much less useful. > > Third option: make it an integer rather than a boolean. > > 0: no validation > 1: current level of validation > 2 and beyond: if we have to extend it later > > Not pretty, I'll admit. So fine to keep as is too if you prefer. > But I do foresee more changes in this area, if history is a guide. > > > > > > Even if per-netns, most likely do not want it writable by netns root > > > with user namespaces. > > > > > > That is the equivalent of ns_capable(CAP_NET_RAW), which is the cause > > > of many crashes due to bad packets ingested by, e.g., a packet socket. > > > > Hmm, yes i get that. Two knobs? a. verify b. the per netns value ro? Both > > on by default? > > A single system wide field is simplest. > > Is there a benefit to making this configurable on a per netns basis? As I tried to explain: a specific container breaks, you decide to trust it, you do not need to trust all. > If so, that's fine too. As long as root-in-namespace cannot modify it, > so readonly indeed. Right. So I envision along the lines of: net.core.virtio_net_hdr_validate_all - validate packets from any netns, netns root can not change it, only host root net.core.virtio_net_hdr_validate - per netns both set by default, validation runs if either is set. -- MST