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=1792936234; b=r5o5wse+DDN7UfHW4CvzR8LxLHxorcQ3lFEQ4zde29uRHWudGoI10AHZedRNV3EE9eee SJ6iKbGHLuq544GvHeJO2pVB6kOGBmKl1falgHSxczp4zZ5zGyX6WtjnCRhdTJlhDPGtp jnohuti/auCEKZvGqErY3ZRcS8mvI/3/lvGbzH55+0mrX0SI14OQCbBuHwdEx+mHT1T5Q g7JU5LU55IDQuwIc87ZMFow6qepfqstb7yx3q/CtW65wv1Filr0Pt1wKOy175qtEZ94hg AZWUgzTg3vvIn+5KbKWzsNWbM/hvhG9QpZNLUGqD1diejo/GYJSzzKRqPh6KHOzVLZw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1792936234; h=DMARC-Filter:DKIM-Signature:Received:X-MC-Unique: X-Mimecast-MFC-AGG-ID:Received: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:In-Reply-To:X-Mimecast-Spam-Score:X-Mimecast-MFC-PROC-ID: X-Mimecast-Originator:Content-Type:Content-Disposition: Content-Transfer-Encoding; bh=ZVC6ZkKoHNQk6TZWCjrTXHjV3/INvwxJlTKOGJKjAvY=; b=NSbiGaIffu+Qe2fP52/RZYbTV9lxkQel8p4n31o5G1cL/aJxlUg3RxyMZLbNoPanRDUE lNoIWUqpYUczQi700AxvaVIev1DkfnqXVqIRap2BxdEUpCrmDEQVNNG0Rulv2FdeJUQrM sRDxbvC+P950FBs++Dh2ZRaWftMFc/Hza8KxweAeBWgB5JT5rqp1gmS2psx95JNIDF/2K QZ5TmC3C0Qu0l+T+1fHIS7de2Fu+RJxoZMOb3BjMler4PA2igkW/qhe5eIc1uXuzgrOSC CoRSkNAx8cR+g1UISzNN8dQ7awL+65aKfSWHW1Jl6EE2p1t0pIzQahvOlphcud0EITQ== 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=FTRJk+93; 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 E13E7606A31D for ; Sun, 25 Oct 2026 13:50:33 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org E13E7606A31D 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=FTRJk+93 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1792936233; 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=ZVC6ZkKoHNQk6TZWCjrTXHjV3/INvwxJlTKOGJKjAvY=; b=FTRJk+93gZ7ocrKg4Vkvg64BNcCef2Zy8K1uxalbnDuXHlL3yoww5h4sYeAYRJ+QYSP/qS La66TUEYnMNn7RSBkXvQ8FWRJM5n5sxX2rdNpil49Oy3iY9eqLbXJuIM0n9zf4FB6trD8s 6bpekvS90dSLpcxyiN1icKa8ocj6INk= Received: from mail-wr1-f70.google.com (mail-wr1-f70.google.com [209.85.221.70]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-336-2Tq9_LowNRS68KEuq6WY5Q-1; Sun, 25 Oct 2026 09:50:31 -0400 X-MC-Unique: 2Tq9_LowNRS68KEuq6WY5Q-1 X-Mimecast-MFC-AGG-ID: 2Tq9_LowNRS68KEuq6WY5Q_1792936230 Received: by mail-wr1-f70.google.com with SMTP id ffacd0b85a97d-48dea677afcso1341933f8f.1 for ; Sun, 25 Oct 2026 06:50:30 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1792936230; x=1793541030; 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=ZVC6ZkKoHNQk6TZWCjrTXHjV3/INvwxJlTKOGJKjAvY=; b=W/RmeYqAbKNWqABJuK7r7Gr7N7z7RwWK7hegQTnKjzju+obb/Z8GGF2VK5PZzaIKsq MgZsVDSTCkQo8w25FhL1hBrPmk9Ev06jR3lvRMFs9hel8pjySIKRoc30VtHa0DNXzXyF j8P3f1/kFtOh+KCnzkXF9yEOTxta27vhpgdcbpxmPpgXAp2ScrdMtK7e54Cund7LRyHz 1T0amG6LltPGGz75Zg1EExHI4XDgEIHMjEqlqGrXPRWTCFRA0zYtyd2wbHG19DsfXWWG XwIkvqT0WSuAhFQnU89T0ZqWA3tY9+r/IWFEVoDrysdkepJ0JHcuypKJfV/RHCxwvFij j4Tg== X-Forwarded-Encrypted: i=1; AKwUvBw87FWMH0Z11cGQgUNF5ZoIefSfbu7gGgo1i4gjd0uvB7+WMtAazuJ0jIV8WSju0v56Foi3HNo97t+3Y/h+rA==@lists.linux.dev X-Gm-Message-State: AFq9FYLx09JQg/iLhbYgqvWEMl2I9t6X2++WQZb7vSNipCXo9dr7Bi8Z 4gWU7H4IzQXervSCe3n8wfCHTIDzBPPxXpzVJjC1vGXFpolfOBltdYlVd8Bf7zoPhIjSOAX1y1v R2E23DkJ6W3E100O+Ie2aMDFxcWZz8QQCAPdgSuFZFZWhvSjshLyory51pFcyORqPOpdD X-Gm-Gg: AYBFou0ZcCQ0WVr8M9TMS/nDyvuHnBpnTU5MDt0vIAkqq9jIOU5bHuLqQjJBzwuD10X oOcYLFMWveWyWR3RFYzzktwMjbPZCYbi/ks7k4ZztpS+unZVy6EYa+sJf29lmaeG+Q7UVQcpKTC 4GtcnD50dypVo+VjLfbuFoIfD5qH7Uf02JgBEqra3KcO7LA+/OEz7roc1+6nx1kQmh/AFmT9eLW eue22+WCbep1uqDt9fJ6QEd4iPUIaLwx+qaCaPKt1swYfoPuHPD9qMYGbreau1hiXALdYffvlbM 5F7+3ZWeXA2tl4xYVUV7TQ4d0ILQDYCCX2St1OG8WFs/JetmlqqaLUgPXvXuohPCTtM= X-Received: by 2002:a5d:490c:0:b0:48e:6f:19b2 with SMTP id ffacd0b85a97d-48e3eb90d56mr5779516f8f.25.1792936229568; Sun, 25 Oct 2026 06:50:29 -0700 (PDT) X-Received: by 2002:a5d:490c:0:b0:48e:6f:19b2 with SMTP id ffacd0b85a97d-48e3eb90d56mr5779460f8f.25.1792936228946; Sun, 25 Oct 2026 06:50:28 -0700 (PDT) Received: from redhat.com ([2a0d:6fc0:1536:fc00:b838:383:1c7:6e81]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48e3ebc3dcbsm10205279f8f.14.2026.10.25.06.50.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 25 Oct 2026 06:50:28 -0700 (PDT) Date: Sun, 25 Oct 2026 09:50:24 -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: <20261025094449-mutt-send-email-mst@kernel.org> References: X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: CXn7WD_7GIZg19Vt__8h93oWr2WA_NJoOq2r0RcfGhg_1792936230 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit 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. Ok, I looked at netdev bot review, and there's another issue. If a tunnel inner packet happens to have a valid header at inner_nh_offset, it will pass all checks, but the transport header can in fact overlap e.g. the real TCP header and checksum will overwrite that. > ------ > > 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 >