From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (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 7C6B4470EA0 for ; Fri, 16 Oct 2026 09:36:22 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.133.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792143384; cv=none; b=GlKVwV3uKxgcGBZIAKaN2S4i83pm3nLKKbn0ZZXxG79IxWXXrqr/dhS8l4jqpDrA1D4IENsPSShPCxSU9swjwBJksRjriRM0B170pr/mM/+I81g3NgOXSsrKLxd+XaR4pk0CKj9TLhjYDchccT67oL4eN2iaPPu8Whk2L7bcvlU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792143384; c=relaxed/simple; bh=RoFTc+bgT+YiyaaL4TBiebP88H3fEi765U7d5X2xO/o=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=d8lbXiGMFCfo0Y3QctXwReGJUBFhNzECR9pZwUTGsyFKOeN3WpQQLNMDMdg0074DMhfuenyDJQBkTzDq2SgfsBYASIAISIJGRa6AqUt3By4ElQJM32y85aoT4843aJkGg6sg2QvpCRvG4rqtu0TYBl9QuLjK2Pko8gFrOGYvX4c= 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=bEgVV/pk; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b=bGix0US4; arc=none smtp.client-ip=170.10.133.124 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="bEgVV/pk"; dkim=pass (2048-bit key) header.d=redhat.com header.i=@redhat.com header.b="bGix0US4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792143381; 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=HeGVMwnnO0pcdPOjq1m3b1Y6CoA/dKS06WTt4589nyM=; b=bEgVV/pk8WPGEfvT4eVopjGrY+GBZ/yf9sB9t47PkLv2u0r7aWiDa/UL28iCI4TA0TK0D/ /itKykoThgiAzgKR7/SjHlstkp5kb7sdtZO6YXWhL9vAwRzrpMHfVUXLYxDshi7O/vYaDp ScT/lgq1ob0QsLGVAB8HGnhA9aGTBds= Received: from mail-wm1-f71.google.com (mail-wm1-f71.google.com [209.85.128.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-70-hAGlmzEeMCinI2GMlt285A-1; Fri, 16 Oct 2026 09:36:16 +0000 X-MC-Unique: hAGlmzEeMCinI2GMlt285A-1 X-Mimecast-MFC-AGG-ID: hAGlmzEeMCinI2GMlt285A_1792143375 Received: by mail-wm1-f71.google.com with SMTP id 5b1f17b1804b1-4a1ad49096fso8264325e9.0 for ; Fri, 16 Oct 2026 02:36:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1792143375; x=1792748175; 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=HeGVMwnnO0pcdPOjq1m3b1Y6CoA/dKS06WTt4589nyM=; b=bGix0US45ngQT0ZD7qvkr5t54S2b4D2/CcCDpdoIKlMQmgLRzEuV751lJXDu2gabkr qMquHiADiUFMwaCmpnLdEfVJFrNofU+/zltb2f1eGVPXzw5Kc/9A8m7SltJshr+EhVkv z5wbbhlvE3Os+wm0KZxsUX1yxqLO+LHM53pdxDiqe2MdxjiPor0zYYMXjjIdW9QPrpGJ X7uVwDVGdtqG1exLJ/zgZXCyr9UXxJMgAL+oRwaYNQ3fIk09on33RXDPiK5Hq0iJ+No9 RyCAUMn8JxMNBeb9o25e6n8SEwwa0CDuDgjV9EkawP7iLZeIaG+M0jjKrV2LWKe6pagm le2Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792143375; x=1792748175; 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=HeGVMwnnO0pcdPOjq1m3b1Y6CoA/dKS06WTt4589nyM=; b=xqWsUhGIqe2T9pIMotFHQ35LBygEu1Lt9pq4M8QWitHBufprTcwANRVlIYZ5GlgUQw 6VH4Z3cxA39sxFeLuV1cqr1UdWq+1w8EdzFZm/faCCxxOq5WKfihiGduJxeyy9Q94vPO l0GD/imKu8nC6gC/GzStcAy6xO7PBNwws3qPd1RCFtWKnmRtkuuml7Cbv0pVm4zr+/Iw tk6q+dKCSlZ419jknQFiEcZBcCjBYpHNHulJk7QXscixiGKqxru2jiaRosX/cjV5rfDw tH2OVj59ZrUSgPMG7QRSrC0xkSh1DL+4aqK4WXlob7PomDnF5ov6+XQkyiUNHYwnqmWT YRgw== X-Gm-Message-State: AFq9FYLuhgZZjbgzqCsk0q+ef2WfrMr1oA9MPZHe6BFoNb4JFcaqqhMB klUacrBFiYc3lZiZ1HjGHc/HGIV5d74T43h3csmHpq4tudNDrGY1TIOde7vN1cXuDhLWQ6EUyne 0sTqMRxGKLMxT4o9spVV8jK8Jix4rjL0CG48apqCo80gB6uUwA8zbdbJAkh/r6Th8Lw== X-Gm-Gg: AYBFou28hEOyGjj4vKvvSdudVDZmXECev4ADgXfvRcmuo6jP0O/vZMTgTUrjWsBryr1 YYJMA0AdHVVoOtg+BTMH4JqHwWAzwnftVcqRo3+wTPVKk7rQQimnyVV3OpORwC3kiwRefYSHcE3 JbjtnaVPIqRL340IVywrAESv/N8TRownixBllYXguWE7A+BOJNdhFwWritn8uD5taCV5LW2CLAy +/G2FJkv2v7XlZa/dMhWUbR+9eA0u3NSpSQoTelOxC0EVNz3coy1gCw0DMtInk8cfQGszolEArr GddKDw3H7gezsKbrBd9u4TvtX2lzpiGjinIHzTXjk7qfBDAKBA2W1odnKR7tx2nrhiWIRg== X-Received: by 2002:a05:600c:c106:b0:4a1:7a1e:6910 with SMTP id 5b1f17b1804b1-4a1c6635d15mr45744525e9.4.1792143374756; Fri, 16 Oct 2026 02:36:14 -0700 (PDT) X-Received: by 2002:a05:600c:c106:b0:4a1:7a1e:6910 with SMTP id 5b1f17b1804b1-4a1c6635d15mr45743975e9.4.1792143374104; Fri, 16 Oct 2026 02:36:14 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:3fd7:5300:3d6b:52a4:a23f:9d0b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a1c8de682bsm42186565e9.13.2026.10.16.02.36.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 16 Oct 2026 02:36:13 -0700 (PDT) Date: Fri, 16 Oct 2026 05:36:10 -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 , Paulos Yibelo , Chris Arges Subject: Re: [PATCH net-next v2 4/7] net: resolve uncommon partial checksums at ingress Message-ID: <20261016053522-mutt-send-email-mst@kernel.org> References: Precedence: bulk X-Mailing-List: linux-kernel@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 Thu, Oct 15, 2026 at 01:43:56PM -0400, Willem de Bruijn wrote: > Michael S. Tsirkin wrote: > > As reported first by Paulos Yibelo (after which > > others, credited below, found more ways the bug can affect users) a > > virtio net header can place CHECKSUM_PARTIAL at any in-packet offset. > > If that state is retained, later checksum completion can modify the > > packet after protocol processing has made decisions from it. > > > > Let's fix that: let's validate csum_start and csum_offset and only keep > > CHECKSUM_PARTIAL when csum_start and csum_offset match a parsed TCP or > > UDP header, while handling VLAN headers, IPv4 options and IPv6 extension > > headers. Complete other non-GSO checksums immediately, before any > > protocol processing runs. > > > > We can't easily "complete the checksum" for GSO we don't recognize - GSO > > assumes knowledge of the protocol. We could segment ignoring the > > checksum then do whatever csum_start and csum_offset say, but that > > seems like an overkill for something that shouldn't happen. > > > > There's some risk here: > > - non-gso packets which can't be parsed get checksum calculated in > > software, adding performance overhead > > - gso packets which can't be parsed get dropped > > > > To mitigate the risks, the following patch will add a sysctl knob to > > bypass the resolution. This is reasonable if the setup is such that > > there is no protocol processing at all. > > > > UDP tunnel headers get the same handling on the inner header. > > > > Packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are unaffected. > > > > Assisted-by: LLM > > Reported-by: Paulos Yibelo > > Reported-by: Chris Arges > > Tested-by: Chris Arges > > Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr") > > Suggested-by: Willem de Bruijn > > Signed-off-by: Michael S. Tsirkin > > --- > > include/linux/virtio_net.h | 251 +++++++++++++++++++++++++++++++++++-- > > 1 file changed, 241 insertions(+), 10 deletions(-) > > > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > > index d6466f96cdd0..357115ff0ec2 100644 > > --- a/include/linux/virtio_net.h > > +++ b/include/linux/virtio_net.h > > @@ -5,7 +5,11 @@ > > #include > > #include > > #include > > +#include > > #include > > +#include > > +#include > > +#include > > #include > > #include > > #include > > @@ -48,6 +52,171 @@ static inline int virtio_net_hdr_set_proto(struct sk_buff *skb, > > return 0; > > } > > > > +/* TODO: nothing virtio specific here, move to ip.h */ > > + > > +/* > > + * Pull and minimally validate the IPv4 header at @nhoff. > > + * Returns the header and stores the transport header offset in > > + * @thoff, or NULL if truncated or malformed. Only the fixed header > > + * is guaranteed linear; callers that need the options or the > > + * transport header must pull further. > > + */ > > nit: comment basically describes the code (what), which is quite > self explanatory. I'd drop. Or else consider converting to kdoc fmt. > > > +static inline struct iphdr *virtio_net_ip4_parse(struct sk_buff *skb, > > + unsigned int nhoff, > > + unsigned int *thoff) > > +{ > > + struct iphdr *iph; > > + > > + if (!pskb_may_pull(skb, nhoff + sizeof(struct iphdr))) > > + return NULL; > > + > > + iph = (struct iphdr *)(skb->data + nhoff); > > + if (iph->version != 4 || > > + iph->ihl < sizeof(struct iphdr) / sizeof(u32)) > > + return NULL; > > + > > + *thoff = nhoff + iph->ihl * sizeof(u32); > > + return iph; > > +} > > + > > +/* Where does the L3 header start, and what protocol is it? > > + * Handles Ethernet and VLAN headers; other devices use the > > + * network header offset the caller set up. > > + */ > > +static inline bool > > +virtio_net_l3_start(struct sk_buff *skb, int *nhoff, __be16 *proto) > > +{ > > + if (skb->dev->type == ARPHRD_ETHER) { > > Only since recent commit 44378d02c5aa ("net: always dissect GSO > packets in __virtio_net_hdr_to_skb()") can skb->dev be relied on to be > non-zero. Yea that commit's pretty important) I'll add that to the commit log. > > We'll have to be careful that this does not get backported to stable > without that. > > Perhaps an explicit precondition test and error return (and > DEBUG_NET_WARN_ON_ONCE) if a NULL skb->dev is encountered. > > OTOH, it results in a hard crash so will be discoverd fast without > that too. > > > > + if (!pskb_may_pull(skb, ETH_HLEN)) > > + return false; > > + *nhoff = ETH_HLEN; > > + *proto = eth_hdr(skb)->h_proto; > > When called from virtio_net_hdr_tnl_to_skb, according to my LLM mac > header may not be set yet. Have not verified yet. > > skb_reset_mac_header(skb) is called inside __virtio_net_hdr_to_skb, > which is then not called yet. > > > + if (eth_type_vlan(*proto)) { > > + *proto = __vlan_get_protocol(skb, *proto, nhoff); > > + if (!*proto) > > + return false; > > + } > > + } else { > > + *nhoff = skb_network_offset(skb); > > The same is true for skb->network_header. Since an uninitialized/zero > value there causes more subtle issues, here an explicit check may be > more valuable (even) than for skb->dev. > > > + *proto = skb->protocol; > > + } > > + return true; > > +} > > + > > > > > /* This function must be called after virtio_net_hdr_from_skb(). */ > > @@ -282,6 +470,35 @@ static inline unsigned int virtio_l3min(bool is_ipv6) > > return is_ipv6 ? sizeof(struct ipv6hdr) : sizeof(struct iphdr); > > } > > > > +/* Do the tunnel offsets match the outer headers in the frame? > > + * The L3 header the tunnel claims must be the one the frame > > + * carries, with UDP following it at @outer_th. > > + */ > > +static inline bool > > +virtio_net_tnl_offsets_ok(struct sk_buff *skb, bool outer_isv6, > > + unsigned int outer_th) > > +{ > > + int nhoff; > > + __be16 proto; > > + unsigned int thoff; > > + int ip_proto; > > + > > + if (!virtio_net_l3_start(skb, &nhoff, &proto)) > > + return false; > > + if (outer_isv6 != (proto == htons(ETH_P_IPV6))) > > + return false; > > + if (!virtio_net_l4_start(skb, nhoff, proto, &thoff, &ip_proto)) > > + return false; > > + > > + return ip_proto == IPPROTO_UDP && outer_th == thoff; > > +} > > + > > +/* > > + * Return value: > > + * 0 - success > > + * >0 - checksum was completed in software (slow path) > > + * <0 - failure > > + */ > > static inline int > > virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > const struct virtio_net_hdr_v1_hash_tunnel *vhdr, > > @@ -293,6 +510,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > unsigned int inner_nh, outer_th, inner_th; > > unsigned int inner_l3min, outer_l3min; > > u8 gso_inner_type, gso_tunnel_type; > > + __be16 inner_proto; > > bool outer_isv6, inner_isv6; > > int ret; > > > > @@ -332,10 +550,13 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > inner_th < inner_nh + inner_l3min) > > return -EINVAL; > > > > + if (!virtio_net_tnl_offsets_ok(skb, outer_isv6, outer_th)) > > + return -EINVAL; > > + > > /* Let the basic parsing deal with plain GSO features. */ > > ret = __virtio_net_hdr_to_skb(skb, hdr, true, > > hdr->gso_type & ~gso_tunnel_type); > > - if (ret) > > + if (ret < 0) > > return ret; > > > > /* In case of USO, the inner protocol is still unknown and > > @@ -353,7 +574,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > } > > > > skb_set_inner_protocol(skb, inner_isv6 ? htons(ETH_P_IPV6) : > > - htons(ETH_P_IP)); > > + htons(ETH_P_IP)); > > if (hdr->flags & VIRTIO_NET_HDR_F_UDP_TUNNEL_CSUM) { > > if (!tnl_csum_negotiated) > > return -EINVAL; > > @@ -368,7 +589,17 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > skb->inner_mac_header = inner_nh + skb_headroom(skb); > > skb->transport_header = outer_th + skb_headroom(skb); > > skb->encapsulation = 1; > > - return 0; > > + > > + /* > > + * We know VIRTIO_NET_HDR_F_NEEDS_CSUM was set so __virtio_net_hdr_to_skb > > + * set CHECKSUM_PARTIAL. > > + */ > > + inner_proto = inner_isv6 ? htons(ETH_P_IPV6) : htons(ETH_P_IP); > > + if (virtio_net_csum_partial_ok_at_offset(skb, gso_inner_type, inner_nh, > > + inner_proto)) > > + return 0; > > + > > + return virtio_net_resolve_csum_partial_mismatch(skb); > > } > > > > /* Checksum-related fields validation for the driver */ > > -- > > MST > > >