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 A24AC4A015D for ; Tue, 13 Oct 2026 18:36:06 +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=1791916569; cv=none; b=NBc2CXEmyPVfTM5yxAsT0s1pR38gKrqCwK23SKS7yYzVbL2AM/e6piNYzJ7MBzI/i0APpFZ2P6E66KaqFpYqsjnKvbLV/dZOYQg7jEqcmk/c+RdUS+Tp/TthT+n1h38CPDRGANg3ZpTWjSXpgLo/klZMnpC2UUsl7/ecYQVea88= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791916569; c=relaxed/simple; bh=MAxPv79SC7ka08t0N1OqDTI4zs64zksbZuXoiMgh/V4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: In-Reply-To:Content-Type:Content-Disposition; b=MmOPt5Nk28ArK1CiQuB9RWkm+1xV+JBHAYha8DeaLc1xUOMk6dQUg86b3QdRVDRhvqlMpjU0VDmod24WgB8Qa/zCrmlFM/IFSClZwNi9fYr6HX8T9eTr4CGpYt+dQ6ncw8x42G0SeQkAsTpEYy7p/S8GZ0S0SpGYvXLSLEPQrxI= 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=GF/N5LSU; 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="GF/N5LSU" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1791916565; 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=kEbFOpHzK1vzTUUdGzQgP9nZrP1KHSfJ40m7HqU+RSk=; b=GF/N5LSUYjH2GDNk91c7+Rj/JgXZouMRKAM/y4y9S1rWG7M86O/m7xIwf5prpNWG8X2n/X 4GNboZWQhwcVXYN9OBuTAWb/VkQK0fwasQfAf8H7q9cnO2JlFo1Hdn5bFZK1kMuZuNQg/W eF9G8nHFjatSmOUQUfzATWNSnzO556Y= Received: from mail-wr1-f69.google.com (mail-wr1-f69.google.com [209.85.221.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-650-mfzNuNoGM2aKaqJ88leMkA-1; Tue, 13 Oct 2026 18:36:04 +0000 X-MC-Unique: mfzNuNoGM2aKaqJ88leMkA-1 X-Mimecast-MFC-AGG-ID: mfzNuNoGM2aKaqJ88leMkA_1791916563 Received: by mail-wr1-f69.google.com with SMTP id ffacd0b85a97d-48589603501so2345900f8f.3 for ; Tue, 13 Oct 2026 11:36:04 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1791916562; x=1792521362; 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=kEbFOpHzK1vzTUUdGzQgP9nZrP1KHSfJ40m7HqU+RSk=; b=hzFdNudPWBhN7IzuqDNojesesn8SbTB3mWg/alx0oZYmJYb8vA9ElnPLcCRoBdjfDV X1OYlieAm2gxpQtliRx5tplV3IUlfsQLXydrY0TC/S5bMPkLywTVbXzIpOMiaeJ0Sw00 /A6wjRuQl0t0KXoPA7ulxfEG0qI6mtZVnNS/VW3GhlmsusEZ1rLkO0ai8h3NWASOmHBL kBB308tf/ZjIW+BPYHK/jdlROyhzXyWPA/xl0nUTsEtcbTciPr5tYhLuqlEPcsCnJXCk lcx6dqU9+iVQIqobQdwvfhOWVqTuUu7KSxeUyBVxzvx57DQ0JOynadKr6inJMuZh1/w7 Kmtg== X-Forwarded-Encrypted: i=1; AKwUvBwQFYJOgDjwhZI+a0d6xlHFkvAzXAFvPH0zLcebwSAtncba7tDs1yT5duI4aGhSaCp+EMuwKQw/i1vWV3l0Gw==@lists.linux.dev X-Gm-Message-State: AFq9FYKN4qYiD013VgBlG8Vdajn9jVv/9JyF4oPl29K1h7Hqu/BB7AGU dYSCJIRDf3ccPzXV1EWN/9erAWSDSF6G0fttZxKeIw7upA9bIwBOyvEny5m/BcM0wC5EFGeJ0lV Qk5ljdsVJra0ioySrO6mToUB3wLAYh2z2ZTNYGr8niBvFltW1Z1Rju8DmCFYK2BjEkCZXZrPQxJ gS X-Gm-Gg: AYBFou0efBPMrXF9jxgXRh5jV4vriLlpV+CGCti8tsKpsD5T++9y6FJWoOiA1qdIafF wHXgiOlJjMNDvcOiTL5fjBYLAEHpJXeBm/GJbIYdszAUNaAc6KJTuIcuacKoqRHEQfj7DAxo8qM +x6BbuUjCO/2KpNk5qkaefKciORqNgL5tHQps5t8mczW6x27ie/fpKpY4FgAfC3F7Xo+ZygZSzy jvcFsqNcg+iGgogxpnenTP9pojmmU0F0hm/HcjKJpvlcCM0+VLVSwJWHf8EHwlLdcLSOHTnPF/g gS3ivIlbs84kwOlDqfClrWi8kfYe2209m5RUxu8vwgRIejhtfDrgexCABkLZwUeg27BJVg== X-Received: by 2002:a5d:5542:0:b0:487:2777:6354 with SMTP id ffacd0b85a97d-48dbaae7239mr20582212f8f.48.1791916562413; Tue, 13 Oct 2026 11:36:02 -0700 (PDT) X-Received: by 2002:a5d:5542:0:b0:487:2777:6354 with SMTP id ffacd0b85a97d-48dbaae7239mr20582159f8f.48.1791916561732; Tue, 13 Oct 2026 11:36:01 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:3fd7:5300:3d6b:52a4:a23f:9d0b]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48de0514ab1sm8613881f8f.0.2026.10.13.11.35.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 11:36:01 -0700 (PDT) Date: Tue, 13 Oct 2026 14:35:57 -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, Max Krasnyansky , Rusty Russell Subject: Re: [PATCH net-next 3/4] net: resolve uncommon partial checksums at ingress Message-ID: <20261013143335-mutt-send-email-mst@kernel.org> References: <20261013070549-mutt-send-email-mst@kernel.org> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: qsiMa--Aj7EJSaU772rNDkAdJEZlW0cF9cfCJIxqL-Q_1791916563 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit On Tue, Oct 13, 2026 at 09:03:04AM -0600, Willem de Bruijn wrote: > On Tue, Oct 13, 2026 at 5:06 AM Michael S. Tsirkin wrote: > > > > On Tue, Oct 13, 2026 at 06:58:41AM -0400, Michael S. Tsirkin wrote: > > > 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 should happen. > > > > > > UDP tunnel headers get the same handling on the inner header. > > > > > > Packets without VIRTIO_NET_HDR_F_NEEDS_CSUM are unaffected. > > > > > > Suggested-by: Willem de Bruijn > > > Signed-off-by: Michael S. Tsirkin > > > Assisted-by: LLM > > > > > > I forgot reported-by tags: > > > > Reported-by: Paulos Yibelo > > Reported-by: Chris Arges > > > > > > > --- > > > include/linux/virtio_net.h | 151 ++++++++++++++++++++++++++++++++----- > > > 1 file changed, 133 insertions(+), 18 deletions(-) > > > > > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > > > index d6466f96cdd00..b181183118b3a 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 > > > @@ -48,15 +52,111 @@ static inline int virtio_net_hdr_set_proto(struct sk_buff *skb, > > > return 0; > > > } > > > > > > +/* Does checksum metadata match a known TCP or UDP header? */ > > > +static inline bool > > > +virtio_net_csum_partial_ok_at_offset(struct sk_buff *skb, u8 hdr_gso_type, > > > + unsigned int nhoff, __be16 proto) > > > +{ > > > + unsigned int thoff; > > > + int ip_proto; > > > + > > > + if (proto == htons(ETH_P_IP)) { > > > + const struct iphdr *iph = ip4_parse(skb, nhoff, &thoff); > > > + > > > + if (!iph || ip_is_fragment(iph)) > > > + return false; > > > + ip_proto = iph->protocol; > > > + } else if (proto == htons(ETH_P_IPV6)) { > > > + const struct ipv6hdr *iph; > > > + int flags = 0; > > > + > > > + if (!pskb_may_pull(skb, nhoff + sizeof(*iph))) > > > + return false; > > > + iph = (const void *)(skb->data + nhoff); > > > + if (iph->version != 6) > > > + return false; > > > + thoff = nhoff + sizeof(*iph); > > > + ip_proto = iph->nexthdr; > > > + if (ip_proto != IPPROTO_TCP && ip_proto != IPPROTO_UDP) { > > > + thoff = nhoff; > > > + ip_proto = ipv6_find_hdr(skb, &thoff, -1, NULL, > > > + &flags); > > Skip this rare case of extension headers? > > > > + if (ip_proto < 0 || flags & IP6_FH_F_FRAG) > > > + return false; > > > + } > > > + } else { > > > + return false; > > > + } > > > + > > > > static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > const struct virtio_net_hdr *hdr, > > > - bool little_endian, u8 hdr_gso_type) > > > + bool little_endian, u8 hdr_gso_type, > > > + bool need_csum_check) > > > { > > > - unsigned int nh_min_len = sizeof(struct iphdr); > > > + typeof(skb->transport_header) old_transport = skb->transport_header; > > > unsigned int gso_type = 0; > > > unsigned int thlen = 0; > > > unsigned int p_off = 0; > > > unsigned int ip_proto; > > > + bool csum_partial_ok = true; > > > > > > if (hdr_gso_type != VIRTIO_NET_HDR_GSO_NONE) { > > > switch (hdr_gso_type & ~VIRTIO_NET_HDR_GSO_ECN) { > > > @@ -69,7 +169,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > gso_type = SKB_GSO_TCPV6; > > > ip_proto = IPPROTO_TCP; > > > thlen = sizeof(struct tcphdr); > > > - nh_min_len = sizeof(struct ipv6hdr); > > > break; > > > case VIRTIO_NET_HDR_GSO_UDP: > > > gso_type = SKB_GSO_UDP; > > > @@ -104,11 +203,11 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > > > > if (!skb_partial_csum_set(skb, start, off)) > > > return -EINVAL; > > > - if (skb_transport_offset(skb) < nh_min_len) > > > - return -EINVAL; > > > + if (need_csum_check) > > > + csum_partial_ok = > > > + virtio_net_csum_partial_ok(skb, hdr_gso_type); > > > > > > - nh_min_len = skb_transport_offset(skb); > > > - p_off = nh_min_len + thlen; > > > + p_off = skb_transport_offset(skb) + thlen; > > > if (!pskb_may_pull(skb, p_off)) > > > return -EINVAL; > > > } else if (gso_type) { > > > @@ -158,8 +257,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > case SKB_GSO_UDP_L4: > > > if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM)) > > > return -EINVAL; > > > - if (skb->csum_offset != offsetof(struct udphdr, check)) > > > - return -EINVAL; > > > if (skb->len - p_off > gso_size * UDP_MAX_SEGMENTS) > > > return -EINVAL; > > > if (gso_type != SKB_GSO_UDP_L4) > > > @@ -167,10 +264,6 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > break; > > > case SKB_GSO_TCPV4: > > > case SKB_GSO_TCPV6: > > > - if (skb->ip_summed == CHECKSUM_PARTIAL && > > > - skb->csum_offset != offsetof(struct tcphdr, check)) > > > - return -EINVAL; > > > - > > > BUILD_BUG_ON(TCP_MIN_GSO_SIZE * GSO_MAX_SEGS < GSO_MAX_SIZE); > > > gso_size = max(gso_size, TCP_MIN_GSO_SIZE); > > > break; > > > @@ -191,6 +284,17 @@ static inline int __virtio_net_hdr_to_skb(struct sk_buff *skb, > > > } > > > } > > > > > > + if ((hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) && !csum_partial_ok) { > > > + int err; > > > + > > > + if (skb_is_gso(skb)) > > > + return -EINVAL; > > > + > > > + err = skb_checksum_help(skb); > > Instead of this variable csum_partial_ok and this branch, could > virtio_net_csum_partial_ok just call skb_checksum_help directly and > drop VIRTIO_NET_HDR_F_NEEDS_CSUM? > > > > + skb->transport_header = old_transport; > > > + return err; > > > + } > > > + > > > return 0; > > > } > > > > > > @@ -198,7 +302,8 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb, > > > const struct virtio_net_hdr *hdr, > > > bool little_endian) > > > { > > > - return __virtio_net_hdr_to_skb(skb, hdr, little_endian, hdr->gso_type); > > > + return __virtio_net_hdr_to_skb(skb, hdr, little_endian, > > > + hdr->gso_type, true); > > Would be great if we can avoid the extra arg and having to update the callers. > > > > } > > > > > > /* This function must be called after virtio_net_hdr_from_skb(). */ > > > @@ -293,6 +398,7 @@ 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; > > > > > > @@ -334,7 +440,7 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > > > > > /* Let the basic parsing deal with plain GSO features. */ > > > ret = __virtio_net_hdr_to_skb(skb, hdr, true, > > > - hdr->gso_type & ~gso_tunnel_type); > > > + hdr->gso_type & ~gso_tunnel_type, false); > > > if (ret) > > > return ret; > > > > > > @@ -352,8 +458,8 @@ virtio_net_hdr_tnl_to_skb(struct sk_buff *skb, > > > return -EINVAL; > > > } > > > > > > - skb_set_inner_protocol(skb, inner_isv6 ? htons(ETH_P_IPV6) : > > > - htons(ETH_P_IP)); > > > + inner_proto = inner_isv6 ? htons(ETH_P_IPV6) : htons(ETH_P_IP); > > > + skb_set_inner_protocol(skb, inner_proto); > > Can drop > > > > if (hdr->flags & VIRTIO_NET_HDR_F_UDP_TUNNEL_CSUM) { > > > if (!tnl_csum_negotiated) > > > return -EINVAL; > > > @@ -368,7 +474,16 @@ 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; > > > + > > > + if (virtio_net_csum_partial_ok_at_offset(skb, gso_inner_type, inner_nh, > > > + inner_proto)) > > > + return 0; > > > + > > > + if (skb_is_gso(skb)) > > > + return -EINVAL; > > This is a risk the commit message will have to call out. I tried with this: > > > 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 should happen. I guess I can add a more detailed explanation about what the risk is? > I don't see a simple way around it. We discussed segmenting here too, > but that requires intrusive changes to all callers too. > Alternatively, > > 1. call segmentation, but only to see it remove the SKB_GSO_DODGY and > thus verify that the TSO/USO packet is valid. Still drop otherwise. > This also does not add overhead, because it would be called later > anyway. > > 2. a failsafe off-by-default sysctl + static_branch that skips the > drop when set. Messy, but so is the situation we're dealing with. Tack this on top or do you feel it's needed straight away.