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[67.216.200.102]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1903bf5d61csm13188815c88.15.2026.10.22.02.16.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 02:16:46 -0700 (PDT) From: Cheng Yongkang To: Nikolay Aleksandrov , Ido Schimmel Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , bridge@lists.linux.dev, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [BUG] net: bridge: tunnel ID zero works on ingress but not egress Date: Thu, 22 Oct 2026 02:16:40 -0700 Message-Id: <20261022091640.3652180-1-teel4res@gmail.com> X-Mailer: git-send-email 2.34.1 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: 8bit Hi all, __vlan_tunnel_info_add() accepts tunnel ID 0, creates a valid tunnel_dst, and inserts the VLAN into the tunnel hash with key 0. Ingress looks up key 0 and retags the frame. The egress path treats tunnel_id == 0 as "not configured" and returns before installing tunnel metadata. The same mapping therefore works in one direction and is inert in the other, while RTM_GETLINK reports it as present. Observed on Linux v7.3, commit 08ab31164c55f20c7a2653de3186ae333470e2c1: VID 100 -> tunnel id 0: ingress VNI 0 is retagged to VID 100 egress emits VID 100 tagged but installs no VXLAN metadata remap VID 100 -> tunnel id 3000: egress immediately produces VNI 3000 Two independent cold boots produced the same result. Either reject tunnel ID 0 as reserved or stop using zero as the egress presence sentinel and make ingress and egress interpret the mapping consistently. This is distinct from candidate BR-063's netlink-size undercount for a tid-zero entry, which has a pending sizing patch. I found no matching functional fix or CVE. The self-contained PoC and both console logs are available on request. This was found with a multi-agent workflow; the ingress/egress asymmetry was reproduced in QEMU. Thanks, Cheng Yongkang