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=1792856549; b=kD9atKGL8gSrVWTR4jqGXuwCdhkUzC0M8eStiJyi/Poba4FHxCCqkWBxHQMJb3Yqkh3a BgymjClkgC5VnEozTvT+V5SIs0Le36UGTMbHiA1vw3VNbqYZcltQUKcbyZnmZ+xlSau+8 ktaIvn5hRtRuqnv6VlAqRod4xDLKd8q8tUZ2jdxqJ3LupYqgEvV/bZFozmEoJvrT4vAqi IL4xP0iMTQWDYysH9mCnInHksGPDjBmoD3sFPv5zy/ADJ4Kg/Ra7pizO3wpDtQS77bFvC Xbd1qVpsB+/FmGe80uyUmodd9PvLuht8K79naRfeGfQQPPx5rthaClPO0+vMDXilmbg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792856549; h=DMARC-Filter:DKIM-Signature:Received:X-MC-Unique: X-Mimecast-MFC-AGG-ID:Received:DKIM-Signature:X-Google-DKIM-Signature: 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=ve5RdvSUQWrWJ7y3heJ0LDreEwIkfgbRRQ56HJPkuoI=; b=LAy2Bn4p7Ik8mWVwXwgsuQ61G8xPIgNavgY0/+pqXguu+18NZRAPHrKpNe4hoe7e5zq5 5RxcU0Tfj+8IS/NyASszF0TSYIPeZ5wToUdfxXt8LOiWAIPyN/l0xccDzl3e8ZkaHUso2 1/G4F70yzh70I6Kw751ZtOo0Q/VPQa2Ij5YKb+AxBu0DFdRSdlrwVISQub4Oz+qd2/kX0 lO+REBlsxP3T1etKvfecqawqPiB/PsRxbA+k4nTws8sIGb12hq3/QqEF9jX/QGEF5iSXN MfV2eI7GKeWj8CWzBZJkLEDsG03iv/FqYeoW8olK79o2/hiIeoyhzqjPy7VxWIjUCHQ== 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=WBvYbDqG; dkim=pass header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=google header.b=fyVHr3Yd; 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 D5C75606A31A for ; Sat, 24 Oct 2026 15:42:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org D5C75606A31A 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=WBvYbDqG; dkim=pass (2048-bit key, unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256 header.s=google header.b=fyVHr3Yd DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792856547; 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=ve5RdvSUQWrWJ7y3heJ0LDreEwIkfgbRRQ56HJPkuoI=; b=WBvYbDqG+1mFq0XvcsAcy5kGqtI5WsHjPrVYdCSXzeugru14SLKOnWKzvTR7fpW21ke5+2 tDH4Izl9lKt22JywCwpSuoz+HNtNuAPEh1WKNFltcT68d6n752M/EZ0N5OIeD3yAxCTKuO Wb7pd6DPip/31LjLlSchEAjNIlB9Q1Y= 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-692-8f9iVrwENAC0VrCcvw38aA-1; Sat, 24 Oct 2026 11:42:21 -0400 X-MC-Unique: 8f9iVrwENAC0VrCcvw38aA-1 X-Mimecast-MFC-AGG-ID: 8f9iVrwENAC0VrCcvw38aA_1792856540 Received: by mail-wm1-f72.google.com with SMTP id 5b1f17b1804b1-4a4654add56so1507605e9.2 for ; Sat, 24 Oct 2026 08:42:21 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=google; t=1792856540; x=1793461340; 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=ve5RdvSUQWrWJ7y3heJ0LDreEwIkfgbRRQ56HJPkuoI=; b=fyVHr3Yd5U6HTwhektAYa7Z2qxUP6o01ozDcwtjeUU7L2CFQS8DkTbjuIoGji2QpQW DDuuiai93ttmjcBfbBqDpr256wEmCrfzR7wHFJUc/6ykcv+blXxav7/y+rmXnS3Zf0Rj YXV4xDzJFb9s/EpspEBSpxhWxEql18P9yOfUmBZW0p/+FI7AFrjMDN/DoKR2Xdzh4qeX ZWMNR2MB7dOHg6H3EDEs+JlNP9mlMIWzQhnLfbIcQkgEBJKV9KWcP2gqa7g37+AzYDUb nitpc43a0w2nvqdYvWh9rDLeUTQuRVb2tEd5An0F0zjdLXw082843kX71kJql36xCBSh ZjaQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792856540; x=1793461340; 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=ve5RdvSUQWrWJ7y3heJ0LDreEwIkfgbRRQ56HJPkuoI=; b=chIZbFp3cZpt96Vr/SIdcKxkuYduv+ILPxpKJNFVdZ6kYZrb+ogtwuS3RYhhlMHcKX b7v07PdoJw2LuC8wFyFmJ09q0ZbMtfYxn/3s3NnUF5ZrOVuEC9JeXT/jNeODRVk8mpUu ch3WtaWyUHtxg52jq4xpg7gss38sNUrtQ9lCHJhMSq8D98mky6HIQf4M2RBUTJOyXxzF +NGCDUt9Yr+hzdYy0zKTY5/q9G5bApvBOsjolcKy+IIpB5yJU5UQJOjWnzdm0wB0iVKH 1qWOUsfzx4B5Kk73WJaRDsGNY5J1HaBSYVG078iuTFeF2i4K3Fk6iaDADF8nHaXtJwNt 97nw== X-Gm-Message-State: AFq9FYLm9hdCq0/kNNWo2/LojK36u2I8TM6bkWRD0OKgCFxhjolEJ99b nrWyDoNjColYcMFc4La9yfv6K2BJd4D0Pp4A54Wdqliu18Dt6Ww71wWGH0LVwp1MKhiVLfogzOM uGNSNkTFCWBKiQq0RvDFI27coCL5I1ra5VL4pCfpuAqwbHOyaLaxi44364lo1mLjXOFmbDSb2x+ mE6yPBj+W9AhV0ATLMWsRIRDA2XfzMw9J9IftW4H0lQhQ= X-Gm-Gg: AYBFou2v6p70IFlUq9XTAKh3z4Ns9UxfFLOVMNbhXhZA/oTrVcBtILQZhN8+xDQnt9q prYqWCgIGuGumzDnb/oXm5H8Rhy12rUWhNZP6lWfx/GMCZlb8jkxY0/YVT2jHw8ktJKHt/CnIlb qiwq+5SKYu0upYMjsKLRo+uqu9GH85swH0U3Tv4iPQ42zB2ia0vzKABvYxeFvb7dbFXsoGn9A/r XIUYtkOhdtBc+js3nw2qBrc9uYCNuQkTTUq5S48Jw0oAy1GTibT1quH03q89rfWuJOB6MoRzcZs dP7TWicZTOhCYK0xxoovAGvDpHozAG7+zt8MDQoeknaDpOaSErMPoMwitHR3rjTlF+BooH0= X-Received: by 2002:a05:600c:46cd:b0:4a3:59c2:b41e with SMTP id 5b1f17b1804b1-4a35ac39396mr36771005e9.4.1792856539769; Sat, 24 Oct 2026 08:42:19 -0700 (PDT) X-Received: by 2002:a05:600c:46cd:b0:4a3:59c2:b41e with SMTP id 5b1f17b1804b1-4a35ac39396mr36770405e9.4.1792856539078; Sat, 24 Oct 2026 08:42:19 -0700 (PDT) Received: from redhat.com ([2a06:c701:73f6:2400:30a8:9e33:7d82:c035]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a00e1b0sm49273505e9.3.2026.10.24.08.42.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 24 Oct 2026 08:42:18 -0700 (PDT) Date: Sat, 24 Oct 2026 11:42:15 -0400 From: "Michael S. Tsirkin" To: linux-kernel@vger.kernel.org Cc: Willem de Bruijn , Chris Arges , =?iso-8859-1?Q?Bj=F6rn_T=F6pel?= , 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 Subject: Re: [PATCH net v6 0/5] more virtio-net csum hardening Message-ID: <20261024113809-mutt-send-email-mst@kernel.org> References: X-Mailing-List: linux-kernel@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: On Fri, Oct 23, 2026 at 11:09:17AM -0400, Michael S. Tsirkin wrote: > > Okay this seems to be converging.... But sashiko did find some issues I > thought are best fixed. Specifically I thought of a better way to handle > short gso in a tunnel - just clear tunnel gso! As a side effect we now > fix up the checksum for these dodgy packets like we did before, instead > of a drop. Good. And more false positives that prompted me to write a > bit more comments. So here goes. > > Apologies for reposting so frequently, I know netdev bot will be unhappy > with that. But Paulos's report made a lot of publicity, there is a lot > of people looking into this, so I feel there's value in defending > against all this class of issues sooner rather than later. > > The issues were mostly found by code inspection, but all reproduced by > me in a VM. Ugh. I found another wrinkle( Firewalls that shape the payload. They are currently seem to simply be hoping most traffic is CHECKSUM_PARTIAL and only looking at that, and that will break. I am not sure what to do yet. Extending the sysctl knob to control what happens if validation fails: pass/drop/complete - is the best I could come up with. Or ignore the issue. Or just forget the complete at input hack and drop if we can't figure it out. > ------ > > As reported first by Paulos Yibelo (after which > others, credited below, found more ways the bug can affect users): > > allowing untrusted hardware to specify csum start/offset for > CHECKSUM_PARTIAL was not a good idea, because, if it edits the packet > outside the actual checksum, and depending on the setup, the networking > stack could be looking at the packet both before and after the edit, and > seeing different results. > > Previously, commit 6785011f8b16 ("ipv4: validate checksum_start before > completing checksum") validated all known instances where this > causes the most grief, but the real fix is to make sure > that either only actual checksum fields are ever edited, > or the checksum is completed before the net stack looks at it, > so it is always consistent. > > > This basically goes back to > what we did before f43798c27684 ("tun: Allow GSO using virtio_net_hdr"), > except in a narrow list of specified known good cases. > > > Summary of the patchset: > > These are probabably net material (and seem to be too big for stable, > or I would recommend backporting there, too): > > net: account for ingress-resolved virtio net hdr state > - accounting, not the fix itself, dependency of the fix > um: vector: trim skbs before verifying the header > - fixes the um receive path: without it the checksum would be > completed over the unreceived tail of the buffer > virtio_net: parse tunnel csum_start little-endian > - bugfix, a dependency of validating the header > net: resolve uncommon partial checksums at ingress > - fix itself > net: add a sysctl to opt out of virtio net hdr checksum validation > - reducing risk of the fix by adding a sysctl to disable it > > These are cleanups, can be deferred to net-next, too: > > net: add ip4_parse() > > Fixes: f43798c27684 ("tun: Allow GSO using virtio_net_hdr") > > Changes since v1: > - reorder patches to fix bisectability, addressing > a comment by Björn Töpel. > - code refactoring, different patch splitup, > a sysctl knob to disable as suggested by Willem de Bruijn. > - fix a bunch of minor issues spotted by LLMs > > > Changes since v2: > > virtio_net: parse tunnel csum_start little-endian > - new patch. correctly parsing the header is a dependency > of validating it, otherwise i do not know what to validate > > net: account for ingress-resolved virtio net hdr state > - make rx_csum_sw counter 64 bit so it won't wrap > (spotted by LLM review) > > net: resolve uncommon partial checksums at ingress > - tunnel fixes to bugs noticed by Willem de Bruijn and > Chris Arges > - restore the csum_offset checks as suggested by Willem > > net: add a sysctl to opt out of virtio net hdr checksum validation > - the knob is no longer writable by root inside a user > namespace: changing it now requires capable(CAP_NET_ADMIN) > suggested by Willem de Bruijn > > net: add ip4_parse() > - comment converted to kernel-doc format (Willem de Bruijn) > > um: vector: trim skbs before verifying the header > - new patch, found by code review > > > Changes since v3: > > net: account for ingress-resolved virtio net hdr state > - um: vector: honor virtio net hdr conversion failures > folded in (Björn Töpel) > - count on tap and virtio_net, too (Willem de Bruijn) > > net: resolve uncommon partial checksums at ingress > - walk the frame on loopback, too: loopback_xmit() runs > eth_type_trans() on it (Willem de Bruijn) > - return the mismatch handling directly, GSO is implied in > the tunnel path so drop there outright, and fold the helper > into its one remaining caller (Willem de Bruijn) > - read the IP version through struct iphdr (Willem de Bruijn) > - document the ipv6_find_hdr() flags choice > > net: add a sysctl to opt out of virtio net hdr checksum validation > - renamed to virtio_net_hdr_validate, in case more validation > is gated by the same knob later (Willem de Bruijn) > - point .data at the value like the neighboring entries, > the per-netns registration rebases it, and the handler reads > the value directly - no ctl_table copy (Björn Töpel, > Willem de Bruijn) > - check the opt-out before parsing: with the knob off, packets > the parser cannot handle were still dropped (Willem de Bruijn) > - include virtio_net.h in net/core/dev.c so the static key > definition sees its declaration (build warning reported by > Jakub Kicinski) > > net: add ip4_parse() > - add the missing kernel-doc Return: section > (Jakub Kicinski) > > > Changes since v4: > > net: account for ingress-resolved virtio net hdr state > - count on tun only: dropped the tap, macvtap, ipvtap and > virtio_net counters (Willem de Bruijn) > - the driver side branches are in their final form here now, > moved from "net: resolve uncommon partial checksums at > ingress" (Willem de Bruijn) > > net: resolve uncommon partial checksums at ingress > - no longer touches the drivers (Willem de Bruijn) > - a packet too small to be GSO: ignore the tunnel GSO request, > same as plain GSO ones, and complete wild metadata in place > (sashiko) > - document the zero copy interaction (sashiko) > - honor a preset skb->protocol on ethernet: the stack uses it, > except on loopback which re-parses the frame (sashiko) > > net: add a sysctl to opt out of virtio net hdr checksum validation > - document the netns lifetime requirement (sashiko) > > net: add ip4_parse() > - pull the whole header, options included, so that the > transport header offset is within the linear data > (Willem de Bruijn) > > > Changes since v5: > > net: resolve uncommon partial checksums at ingress > - read both skb->protocol and the frame ethertype: do not > validate when they disagree, instead of preferring the > preset protocol; same check after the IP version inference > where there is no L2 header (Willem de Bruijn) > - pull the IPv4 options in the helper as introduced, with the > transport header offset computed before the pull > (Willem de Bruijn) > - fold the trivial protocol calculation cleanup, formerly a > separate patch, in (Willem de Bruijn) > > net: add ip4_parse() > - the options pull moved to the helper introduction in > "net: resolve uncommon partial checksums at ingress" > > Tested: full suite on the final tree, tunnel included. > um part compiled only. > > > Michael S. Tsirkin (5): > net: account for ingress-resolved virtio net hdr state > um: vector: trim skbs before verifying the header > virtio_net: parse tunnel csum_start little-endian > net: resolve uncommon partial checksums at ingress > net: add a sysctl to opt out of virtio net hdr checksum validation > > Documentation/admin-guide/sysctl/net.rst | 19 ++ > arch/um/drivers/vector_kern.c | 6 +- > arch/um/drivers/vector_transports.c | 4 +- > drivers/net/tap.c | 4 +- > drivers/net/tun.c | 41 ++- > drivers/net/virtio_net.c | 2 +- > include/linux/virtio_net.h | 319 ++++++++++++++++++++++- > include/net/netns/core.h | 1 + > net/core/dev.c | 7 + > net/core/net_namespace.c | 1 + > net/core/sysctl_net_core.c | 50 ++++ > net/packet/af_packet.c | 4 +- > 12 files changed, 441 insertions(+), 17 deletions(-) > > -- > MST >