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[34.48.4.250]) by smtp.gmail.com with ESMTPSA id 00721157ae682-82006078e91sm13105417b3.41.2026.08.03.20.04.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Aug 2026 20:04:54 -0700 (PDT) Date: Mon, 03 Aug 2026 23:04:54 -0400 From: Willem de Bruijn To: Jakub Kicinski , Willem de Bruijn Cc: Qihang , netdev@vger.kernel.org, daniel.zahka@gmail.com, davem@davemloft.net, edumazet@google.com, pabeni@redhat.com, horms@kernel.org, stable@vger.kernel.org Message-ID: In-Reply-To: <20260803192228.49a49867@kernel.org> References: <20260730082925.93759-1-q.h.hack.winter@gmail.com> <20260730082925.93759-3-q.h.hack.winter@gmail.com> <20260803192228.49a49867@kernel.org> Subject: Re: [PATCH net v5 2/2] packet: use consistent hard_header_len in TX_RING send path Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Jakub Kicinski wrote: > On Thu, 30 Jul 2026 05:22:21 -0400 Willem de Bruijn wrote: > > Qihang wrote: > > > tpacket_snd() reads dev->hard_header_len independently for skb > > > allocation and header construction in tpacket_fill_skb(). Concurrent > > > netdevice reconfiguration can therefore make the reserved headroom > > > smaller than the amount later pushed, or make copylen - hard_header_len > > > negative. > > > > > > Snapshot hard_header_len once before processing ring frames and use it > > > for the frame limit, headroom allocation, copy length, and skb > > > construction. Pass the snapshot to tpacket_fill_skb(). > > > > > > The separate SOCK_DGRAM consistency problem between hard_header_len and > > > header_ops->create is not addressed here. > > > > > > Fixes: 69e3c75f4d54 ("net: TX_RING and packet mmap") > > > Cc: stable@vger.kernel.org > > > Signed-off-by: Qihang I missed this before, but Qihang is that your full name? https://www.kernel.org/doc/html/latest/process/submitting-patches.html#sign-your-work-the-developer-s-certificate-of-origin > > > > Reviewed-by: Willem de Bruijn > > Willem, does the *shiko feedback look like false positives? > Both instances seem to provide different feedback, if I'm reading my own > tea leaves right Claude discarded the Gemini feedback about a panic > as a hallucination.. > > https://sashiko.dev/#/patchset/20260730082925.93759-2-q.h.hack.winter@gmail.com > > https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260730082925.93759-2-q.h.hack.winter@gmail.com If I read Gemini feedback correctly, all reports are about the current solution falling short of fixing the instance of this race condition with dev_hard_header(), which reads dev->hard_header_len directly. The patch indeed mentions this limitation. As well as the same issue with dev_validate_header(), which the commit does not list as limitation. But that one is only reached with variable length L2 protocols. Side note, in net-next I can probably remove header_ops.validate now that ax25 is gone, and with that all of dev_validate_header. No other variable length L2 protocol ever implemented that callback. But that won't help older kernels, of course. I think it's fine to remove that CAP_SYS_RAWIO branch in the fix, which never had much value anyway. It was there to allow testing purposely bad input or so.