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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ec234277b8sm2521988e0c.8.2026.10.24.09.08.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 24 Oct 2026 09:08:56 -0700 (PDT) Date: Sat, 24 Oct 2026 12:08:55 -0400 From: Willem de Bruijn To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org Cc: Willem de Bruijn , Chris Arges , =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= , Phil Sutter , Jason Wang , =?UTF-8?B?RXVnZW5pbyBQw6lyZXo=?= , 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 Message-ID: In-Reply-To: <20261024113809-mutt-send-email-mst@kernel.org> References: <20261024113809-mutt-send-email-mst@kernel.org> Subject: Re: [PATCH net v6 0/5] more virtio-net csum hardening 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=utf-8 Content-Transfer-Encoding: 7bit Michael S. Tsirkin wrote: > 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. Sounds like such users will just have to disable the sysctl for now: pass. And update their firewall, then reenable the sysctl? Does adding a third drop option help in any way? The sysctl is the safety valve to go back to old behavior.